Brushing Pansy (Viola tricolor L.) Transplants - DigitalCommons ...
Brushing Brushing pansy (Viola tricolor tricolor LJ L.) transplants: a flexible, effective effective method for controlling controlling plant size L.c. L.C. Gamer, Garner, F.A. F.A. Langton Langton
**
Horticulture Research International, Wellesbourne, Wellesbourne, Wanvick, Wclrwick, CV35 CV35 9EF, 9EF, UK UK
Abstract Though brushing brushing is an effective method for controlling controlling excessive excessive elongation elongation in many species, its adoption by the commercial plug transplant transplant industry industry will depend on the ease and flexibility flexibility of its application, L.) seedlings growing at a density density of application. Brushing was applied to pansy (Viola tricolor L) ~ 2 by daily stroking with 20/20 1500 plants m m-2 20/20 gauge netting, netting. In dose response experiments, experiments, final final petiole length appeared to approach a lower asymptote asymptote as number number of brush strokes increased, and the number reduction in length increased under environmental number of strokes required to give near full full reduction environmental conditions conditions favouring favouring extension extension growth, growth. Ten or 20 daily strokes strokes, typically typically gave a 25-30% reduction reduction in petiole elongation elongation without causing plant damage or affecting subsequent subsequent flowering. flowering. Reductions Reductions in shoot dry weight tended to parallel those for petiole length. Increasing Increasing the interval interval between strokes by up to 10 min brushing. There was no rain resulted in similar reductions reductions as continuous continuous brushing. brushing 1 or 2 times difference between brushing brushing the plants at 09:00 or 16:00 h, or between brushing day ~ 1.I. Plants required at least 5 days treatment week week-- 1~ for significant significant size control. Brushing is an effective, effective, flexible flexible method for controlling controlling petiole length in pansy and it should find find application application in the commercial transplant transplant industry.
1. Introduction Introduction A difficulty faced by transplant growers is to produce plants of a specified size at the scheduled time. Control of bedding plant growth with chemical growth regulators is a common practice, but the use of these chemicals is expensive, difficult and increasingly increasingly restricted. Inexpensive, non-chemical methods of height control are needed which can be
easily adapted for commercial use. Mechanical stimulation (MS) can reduce stem and I). One type petiole elongation in a number of species (Biddington, (Biddington, 1986, 1986, Latimer, 199 1991). of MS, brushing, allows many plants to be stimulated at the same time. Brushing Brushing can significantly reduce petiole length in pansy (Viola tricolor L.) without causing plant damage (Gamer (Garner et aI., al., 1997), 1997), and there is the potential to use this technology in commercial operations if systems of brushing can be devised which are simple and flexible in their application. To this end, a series of experiments was conducted to determine the appropriate dosage and timing of brushing for pansy transplants and to characterise the daily amount, timing and number of days per week of brushing required for effective size control.
2. Materials Materials and methods 2.1. Plant culture Pansy seedlings ('Turbo Mix'), provided by W.J. Findon and Sons (Stratford-upon (Stratford-uponAvon, UK) were grown in 165 'plug trays' at a density densily of 1500 plants m -2. -2. Plants were maintained in a glasshouse at approximately ]8°C 18°C without supplementary lighting and 19: 19 (Vitax UK Limited. were watered and fertilised with Vitafeed 19: 19:19:19 Limited, Leicester, UK) as required. Plants were brushed by hand with a flexible 20/20 2 0 / 2 0 gauge netting (Bradley Lomas Electrolok, Ltd, Sheffield, UK), and each back and forth movement was counted as a single brush stroke. The netting was dragged carefully across the plant canopy to provide similar stem and petiole flexure with each stroke. MS was, therefore, provided by tactile stimulation of petioles and leaves, and by back and forth movement of entire shoots. Treatments were begun at the cotyledon stage of growth and continued continued until the plants were of a saleable size, typically after 25-30 25-30 clays days of treatment.
2.2. Dose response A previous experiment in which only three dosage levels of brushing were investi investigated showed that pansy petiole length could be significantly reduced by 10 or 20 brush strokes day - I1 without causing damage and without the large reductions in leaf area and shoot dry weight typically caused by 40 brush strokes day - Ii (Gamer (Garner et aI., al., 1997). 1997). Experiments were conducted, therefore, to examine more closely the relationship between the number of brush strokes per day and size reduction and, if possible, to determine an optimum dosage. Plants received 5, 10, 20, 30 or 40 brush strokes each morning, or were left untreated.
2.3. Interval between brush strokes Two experiments were conducted conducted to determine whether the time interval between brush strokes could be increased and still result in the same amount of height control as continuous brushing. The total daily stimulation remained constant, but the time interval between strokes was varied. Plants were either untreated, brushed continuously, or were
brushed with a 1- or 10-min l 0-min interval between paired back and forth strokes. A total of 20 brush strokes day day-- It were applied in the first experiment, and 10 or 20 strokes day - 1~ in the second experiment.
2.4. Time of of day Two experiments were conducted conducted to determine the most appropriate time of day for effective brushing. Plants were either untreated, or were brushed in the morning (at approximately 09:00 h), in the afternoon (at approximately 16:00 h) or twice a day (half in the morning and half in the afternoon). The total number of strokes was the same for each treatment (20 day-I day -~ in the first experiment, and 10 dayday -~I in the second experiment). 2.5. Times per week It would be commercially beneficial if transplants did not have to be brushed every day to maintain control of petiole elongation. Therefore, experiments were conducted conducted in which plants were either untreated or were brushed in the morning each day, 5 days a week (Monday to Friday, inclusive), or every other day. Twenty brush strokes day-I day- I in the second experiment. were applied in the first experiment and 10 strokes day day-~ 2,6. 2.6. Data collection and experimental design At the end of the treatment period, petiole length and shoot dry weight were measured, and any damage noted. Leaf area and the number of leaves per plant were also recorded in experiments concerning the time of day and the number of days per week of application. Experiments were typically conducted conducted using a randomised complete block design with six replications. However, a completely randomised design with four replications was used for dosage experiments. In all experiments, a quarter tray was used as the experimental unit, and ten plants from each plot were sampled for measurement. Guard rows one to two cells wide surrounded surrounded all experimental units, so that edge plants were not sampled. All the experiments were repeated in time. The first set of experi experiments was conducted conducted between 27 March and 2 May, 1996, 1996, and the second between 13 May and 10 June, 1996. 1996. During the second set of experiments, shade screens were used to prevent leaf damage on sunny days. Data were analysed using analysis of variance, the Chi-square test of homogeneity and Fisher's protected LSD with 95% confidence level (MINITAB, 1995), 1995),
3. Results Results 3,1. 3.1. Dose response In both experiments, the mean petiole length and mean shoot dry weight of brushed plants were significantly less than those of untreated plants (Table 1), l). There were no significant differences between the five brushing treatments for either variate in Experi Experi-
Table 11 Table The The effect effect of the the number number of brush brush strokes per day day on on the the growth growth of pansy pansy transplants transplants Brush strokes per per day Brush
Petiole Petiole length length (mm) (mm)
Shoot Shoot dry dry weight weight (mg)
Expt I1
Expt 2
Expt 11
None 5 10 10 20 30 40
12.8 12.8 10.0 9.3 9.6 10.1 10.1 9.8
20.2 2(I.2 17.4 1;'.4 15.0 14.0 13.3 13.3 12.8 12.8
59 52 50 51 51 45 50
vs untreated
untreated Brushed vs Linear trend
.
SE LSD LSD005 (18 d.f.) o05 (I8
NS
.
.
.
. * **
.
0.55 1.62 1.62
0,85 0.85 2.51 2.51
.
Expt 2 80 75 63 62 49 54
. NS
. * ~ *
4.1 4.1 -
4.1 4.1
12.3
12.3
NS. NS, '* •. . . . ., . ' • , ' , main effects within column not significant significant at P == 0.05 or significant significant at P < 0.001,0.01 0.001, 0.01 or
or respectively. Trends other than linear were non-significant non-significant at P == 0.05.
0.05. 0.05, respectively.
merit 1. However, H o w e v e r , in Experiment E x p e r i m e n t 2, a significant s i g n i f i c a n t linear l i n e a r trend t r e n d over o v e r the five brushing brushing ment treatments t r e a t m e n t s was w a s shown s h o w n (p ( P = 0.001), 0.001), with w i t h reductions r e d u c t i o n s in petiole petiole length l e n g t h and a n d shoot s h o o t dry w e i g h t as the number n u m b e r of o f brush b r u s h strokes strokes increased. increased. weight A l t h o u g h trends other o t h e r than linear l i n e a r were were formally f o r m a l l y non-significant n o n - s i g n i f i c a n t at P P = 0.05 0.05 in Although E x p e r i m e n t 2, visual inspection i n s p e c t i o n of o f the data data (Table ( T a b l e I) 1) suggested s u g g e s t e d that both b o t h height h e i g h t and and Experiment shoot s h o o t dry d r y weight w e i g h t approached a p p r o a c h e d a lower l o w e r limit l i m i t as the number n u m b e r of o f brush b r u s h strokes strokes increased. increased. This + b //(1 (! + + ex), cx), where where x = = number n u m b e r of of T h i s was w a s modelled m o d e l l e d by b y fitting the function f u n c t i o n yy = a + brush petiole b r u s h strokes, strokes, a a = the lower l o w e r asymptote a s y m p t o t e and and a a + + b = response r e s p o n s e when w h e n x = O. 0. For F o r petiole (see Fig. Fig. 1), this m model to the the ddata than did did the the llinear model llength e n g t h (see o d e l ggave a v e aa bbetter e t t e r fit to a t a than i n e a r ttrend rend m odel control). R Respective lack ooff m model for the the ttwo ((with w i t h uuntreated n t r e a t e d control). e s p e c t i v e lack o d e l fit sums s u m s ooff squares s q u a r e s for wo 2 m o d e l s were 1.640 m m 22 aand n d 9.451 m 2, oth w ith 3 3 d.f. s t i m a t e s ooff pparameters a r a m e t e r s were: , b models were 1.640 mm 9.451 m mm both with dJ. EEstimates were: mm mm); bb==9 . 9.21 mm (SE aa== 11.09 11.09 m m ((SE S E ==1 . 31.39 9 ram); 21 m m (SE ( S E == 1.44 1.44 rmm); a m ) ; ce==0 .0.1101 1101 ( S E == 0.0583). Similarly, was oobtained for the the aasymptotic model the linear linear 0.0583). Similarly, aa bbetter e t t e r fit was b t a i n e d for symptotic m o d e l tthan h a n the model for shoot dry weight, weight, w with lack ooff rresponse esponse m o d e l ((with w i t h uuntreated n t r e a t e d ccontrol) o n t r o l ) for s h o o t dry i t h rrespective e s p e c t i v e lack
22
20 ~ EEl8 v J~
SE~ SEi
16
B
._o 12
~- 10 8
i
o
~
o
i
i
i
o i
0 10 20 20 30 30 40 40 Number Number of of brush brush strokes strokes I. Relationships between numbers of brush strokes strokes and petiole petiole length in Experiment 1I (C)) (0) and Fig. 1. (.). Fitted curves are for the function 3' y= = a+ a + b/(lI+ + cx) ex) (see text). Experiment 2 (Q).
Ie
model fit sums of squares of 271.34 mg 22 and 428,10 428.10 mg 22 (dJ. (d.f. == 3). Estimates of parameters were: a = 37.8 mg (SE = 14.7 mg); rag); b = 43.2 mg (SE = 13.7 mg); c = 0.0530 (SE = = 0.0463). No such trend was apparent for Experiment 1, although it is possible that the response to brushing was essentially as in Experiment 2, but already approaching full expression after the application of five brush strokes. Fits to the asymptotic model (Fig. I) 1) and the linear response model (with untreated control) for petiole length were similar, m m 22 and 1.517 mm 22 with respective lack of model fit sums of squares of 1.590 mm (dJ. (d.f. == 3). Similar fits were also given to the two models for shoot dry weight, lack of (d.f, == 3). model fit sums of squares being 70.71 mg 22 and 80.70 mg 22,, respectively (dJ. Though 5 strokes day-I d a y - J did cause a statistically significant decrease in petiole length in Experiment 2 (a decrease in petiole length of about 14%) the stimulus was judged to be insufficient insufficient to be of practical importance to the grower. In both experiments, 30 or 40 brush strokes day-I d a y - f caused noticeable plant damage. interL,al between strokes 3.2. Time interval
In both experiments, brushing significantly significantly reduced petiole length, but there were no significant differences between the three brushing treatments (Table 2). Shoot dry weight was not significantly significantly affected by brushing and there was no noticeable damage in either experiment. More importantly, contrasts between continuous and non-continuous non-continuous brushing and between 1- and 10-min 10-rain intervals were not significant for any measured variate in either experiment. 3.3. Time of o f day Petiole length, leaf area and shoot dry weight were all significantly significantly decreased by brushing, though there were no significant differences between the three brushing
Table Table 2 The between paired paired brush brush strokes pansy transplants The effect effect of varying varying the the time time interval interval between strokes on on the the growth growth of pansy transplants Method brushing Method of brushing
Petiole Petiole length length(mm) (ram)
Shoot weight (mg) Shoot dry dry weight (mg)
Expt Expt 1l
Expt Expt 2
Expt 1l
Expt Expt 2
None None Continuous Continuous I-min l-min intervals intervals 10-rain intervals intervals 10-min
12.2 12.2 10.0 10.0 9.5 9.5 9.6
18.5 18.5 17.1 17.1 16.3 16.3 16.1 16.1
63 63 60 54 56 56
65 65 71 71 70 70 64
Brushed vs vs uuntreated ntreated Brushed Continuous Continuousvs vs non-continuous non-continuous 1- vs vs 10-min 10-minintervals intervals 1-
. NS NS NS NS
NS NS NS NS
NS NS NS NS NS NS
NS NS NS NS NS NS
0.47 0.47 1.57 1.57
0.92 0.92
SE SE LSD LSD005 (15 dJ.) d.f.) o05 (15
.
.
.
-
2.8 2.8
4.1 4.1
-
-
NS••" ,. .'. NS, . . .' , , '. main maineffects effects within within column column not not significant significantat P == 0.05 0.05 or significant significantat P < 0.001, 0.001, 0.01 0.01 or 0.05, respectively. 0.05, respectively.
Table 3 The effect of time of day of brushing on the growth of pansy transplants Petiole length (mm)
Leaf area (cm 22))
Shoot dry weight (mg)
Expt I1
Expt 2
Expt I1
Expt 2
Expt I1
None Morning and afternoon Morning only Afternoon only
15.4 12.0 12.8 12.3
18.6 16.6 16.1 15.6
12.35 10.56 10.31 t0.31 10.52
15.57 13.44 11.94 12.58
80 73 70 72
88 77 70 73
Brushed vs untreated I1 vs 2 applications day - Ii Morning vs afternoon
.
. NS NS
NS NS
Time and frequency of daily brushing
SE LSDo.o5 (J (155 d.f.) LSDoos
NS NS
.
.
. NS NS
0.45 l.l5 1.15
0.76 1.64
.
. . NS NS
.
0.530 l.l16 1.116
. . NS NS 0.738 2.328
3.5 -
Expt2 Expt 2
4.0 11.6 l 1.6
NS.••• NS, * . . . .,. •. , ., main effects within column not significant at P P = 0.05 or significant at P P < < 0.001, 0.01 or 0.05, respectively.
treatments t r e a t m e n t s for f o r any a n y of o f these t h e s e variates v a r i a t e s (Table ( T a b l e :3). 3). The T h e number n u m b e r of o f leaves l e a v e s per p e r plant p l a n t appeared appeared independent i n d e p e n d e n t of o f the t h e time t i m e of o f day d a y of o f bbrushing r u s h i n g in both b o t h experiments e x p e r i m e n t s (data ( d a t a not n o t shown) s h o w n ) and and there t h e r e was w a s no n o noticeable n o t i c e a b l e damage d a m a g e in either e i t h e r experiment. e x p e r i m e n t . Furthermore, F u r t h e r m o r e , contrasts c o n t r a s t s bbetween e t w e e n I1 and and 2 2 treatment t r e a t m e n t applications a p p l i c a t i o n s day d a y -1, - 1 , and a n d bbetween e t w e e n morning m o r n i n g and a n d evening e v e n i n g treatments, t r e a t m e n t s , were were n o t significant s i g n i f i c a n t for f o r any a n y measured m e a s u r e d variate v a r i a t e in either e i t h e r experiment. experiment. not 3.4. Times pper e r week week Treated T r e a t e d pplants l a n t s typically t y p i c a l l y had h a d significantly s i g n i f i c a n t l y shorter s h o r t e r ppetioles e t i o l e s than t h a n untreated u n t r e a t e d pplants l a n t s (Table (Table 4). 4). In I n Experiment E x p e r i m e n t I, 1, there t h e r e was was a a significant s i g n i f i c a n t nnegative e g a t i v e linear l i n e a r relationship r e l a t i o n s h i p bbetween e t w e e n ppetiole etiole length l e n g t h and a n d the t h e number n u m b e r of o f times t i m e s pper e r week w e e k that t h a t the t h e pplants l a n t s were w e r e treated. t r e a t e d . Brushing B r u s h i n g every every
Table 4 The effect of the frequency of brushing per week on the growth of pansy transplants Frequency of brushing
Petiole length (mm) (ram)
Leaf area (cm 22))
Shoot dry weight (mg)
Expt Il
Expt 2
Expt Il
Expt 2
None Alternate days per week 5 consecutive days week -I week-i 7 days week - Ii
12.4 11.5 I 1.5 10.4 9.6
16.8 15.4 14.4 14.2
9.28 8.34 7.80 7.06
13.38 12.04 10.63 11.73
65 61 S6 56 S3 53
80 75 68 7S 75
F test overall Brushed vs untreated trend a Linear trend"
" ** * ** **
NS NS NS
*~* *" * **
NS NS NS
** ~ ** " ,, x
NS NS NS
0.90 -
0.270 0.675
0.841 -
SE LSD LSDoo5 (155 dJ.) d.f.) oo5 (J
0.35 O.3S 1.06
Expt I1
2.1
2.1 4.0
Expt 2
4.2 -
"Based aBased on brushing 3.S, 3.5, 5 or 7 days week week-- Ii..
P< NS, ••• * . . . ., •• , main effects within column not significant at Pp,; := 0.05 or significant at P < 0.001 or 0.01,
0.01, respectively. There were no significant quadratic trends.
trends.
other other day day was was the the only only treatment treatment that that did did not not provide provide aa sufficient sufficient or or significant significant decrease decrease in petiole petiole length length relative relative to to unbrushed unbrushed plants. plants. A A similar similar trend trend was was noted noted for the the petiole petiole in length data data in in Experiment Experiment 2, 2, though though this this was was not not significant. significant. There There was was aa significant significant length negative relationship relationship between between both both the the leaf leaf area area and and shoot shoot dry dry weight weight and and the the number number of of negative times per per week week that that the the plants plants were brushed brushed in Experiment Experiment 1. 1, The The leaf leaf area area and and shoot shoot dry weight weight were were not not significantly significantly affected by any of of the the brushing brushing treatments treatments in Experiment 2. The The number number of of leaves per per plant plant seemed seemed independent independent of of the the brushing brushing Experiment treatments in both both experiments experiments (data (data not not shown). shown), There There was was no noticeable noticeable plant plant damage damage treatments in either either experiment. experiment.
4. Discussion Discussion 4. Environmental conditions conditions in experiments to detemfine detemline the the effects of of dosage were Environmental that petiole lengths lengths were substantially substantially greater in Experiment Experiment 2 (summer) than in such that Experiment 1 (spring). Under Under the conditions conditions of of Experiment Experiment 2, length length approached approached a lower lower Experiment limit with increasing number of strokes. A similar asymptotic response may have been shown in Experiment !I but but was missed because as few as five brush strokes invoked reduction. Whether Whether or not this is an accurate interpretation interpretation of of the near maximum reduction. brushing, it is apparent that numbers of biological response of pansy to stimulation by brushing, required to achieve full or near full growth reduction reduction are likely to be greater strokes required under conditions favouring extension growth than under conditions less favourable to growth. In practice, 10-20 10-20 brush strokes can be expected to give a commercially useful % reduction) at any time of year without causing plant damage, response (25-31 (25-31% damage. Associated reductions in shoot dry weight are likely to be of a similar or smaller percentage magnitude. In a previous experiment with tomato (Lycopersicon esculentum esculentum MilL) Mill.) transplants, the response r e s p o n s e to brushing b r u s h i n g was was also easily saturated saturated (Garner ( G a r n e r and Bjorkman, BjiSrkman, 1996), as it was with the pansy transplants in Experiment I. 1. Other re researchers have reported a negative relationship between the amount of stimulation given and the plant height of a number of species (Beyl and Mitchell, 1977, Heuchert and Mitchell, 1983, Autio et aI., al., 1994), and these results are similar to those obtained with the pansy transplants in Experiment 2. What is consistent among all of these experi experiments is that a relatively small amount of brushing brushing: can provide a significant and noticeable reduction in transplant size. Further brushing of the plants only increases the risk of damage and the effort associated with brushing, without substantially increasing the benefits of the treatment. Pansy plants which had been brushed continuously 20 times day - j),, 7 days week -)~,, were subsequently potted up in the greenhouse alongside control plants, and brushing was discontinued. This demonstrated that brushing had no adverse effect on flowering after transplanting; there was no delay in the appearance of flowers and no increase in the the number number of of days days to to 50% 50% flowering flowering (data (data not not: shown). shown). Brushing Brushing also also caused caused no no damage to to the the flowers. flowers. The The results of of the the experiments experiments on on increasing increasing the time interval interval between strokes strokes were consistent consistent with those of of aa similar similar experiment experiment using tomato transplants (Garner (Garner and and Bjorkman, Bj6rkman, 1996), 1996). For For both species, species, the time interval interval between strokes strokes can can be at at least least 10 10
min long, and still result in similar size control as continuous stimulation. It is not necessary for pansy plants to receive daily brushing in a series of continuous strokes. This provides flexibility for commercial application, especially if the technique is to be automated. The effectiveness of brushing was not significantly influenced by the time of day of its application. The response of tomato plants to MS is also typically unaffected by the time of day of treatment application (Heuchert and Mitchell, 1983, 1983, Gamer Garner and Bjorkman, BjSrkman, 1996), 1996), though chrysanthemums (Dendranthema (Dendranthema X × grandiflorum (Ramat.) Kitam.) are slightly more sensitive to MS in the morning (Beyl and Mitchell, 1977). 1977). Results from the pansy experiments, however, are nOll no~t consistent with research showing that tomato plant height is more greatly reduced by two or more small daily vibration treatments than by one daily equivalent treatment (Mitchell et aI., al., 1975, Piszczek and Jerzy, 1987). 1987). This difference between the response of tomato and pansy plants could be real, but it might also reflect, in part, the increased amount of handling required to place the tomato plants on a gyratory shaker several times each ,each day. In commercial practice, the timing of brushing pansy transplants should be extremely flexible. There were no statistical differences between treating the plants once each day (20 or 10 strokes) or twice each day (ten or five strokes), or between treating them in the morning or the afternoon. The choice of the best time of day for brushing can be left to the individual grower, and could even be determined on a daily basis to minimise interference with production practices and to avoid brushing the plants when they are either wilting or wet. The results of experiments on the number of treatments per week were consistent with previous research in which decreasing the number of days per week on which lettuce (Latuca satiea sativa L.) transplants were brushed decreased the effectiveness of treatment (Wurr and Fellows, 1986). 1986). However, for both lettuce and pansy transplants, some reduction in the frequency of brushing can be tolerated. In Experiment I, 1, brushing for only 5 days week -~I provided a significant decrease in petiole length while minimising reductions in leaf area and shoot dry weight. Whilst brushing at least Ii time day-l d a y - ~ has been recommended for the height control of tomato and cucumber (Cucumis sativus L.) transplants (Latimer, 1992), 1992), this does not appear to be necessary for pansy transplants. It is concluded that brushing is a sufficiently flexible technique to be integrated with commercial production practices. Pansy transplants require only a small amount of daily stimulation to achieve maximum growth reduction, and the dosage can be adjusted to suit the growth rate of the crop. It is likely that the degree ,degree of growth control achieved with 10-20 10-20 brush strokes day-I day- ~ will fully satisfy commercial requirements in the spring and autumn periods when the extension growth of pansy is naturally limited, but some additional control by the use of chemical growth regulators may be required in the more difficult summer period. However, brushing will greatly reduce the numbers of growth regulator applications needed or the concentrations required. The timing of the stimula stimulation is not critical. Plants can be brushed at a time when the grower finds it most convenient, and brushing does not have to be applied continuously. ,continuously. Plants do not have to week-I is likely to be be brushed every day, although treatment on at least 5 days week-~ necessary for effective size control. The response of plants to MS varies with species,
but this and but and other other work w o r k consistently consistently show s h o w that that the magnitude m a g n i t u d e of of the response response to MS M S is not by altering not greatly greatly affected affected by altering the dosage dosage or or timing tinting of of the stimulation. stimulation. Some S o m e form f o r m of of mechanisation m e c h a n i s a t i o n is essential essential in order order to exploit exploit the utility of o f brushing brushing in commercial practice, and c o m m e r c i a l practice, and trials to achieve a c h i e v e this have have begun b e g u n at W.J. W.J. Findon Findon and and Sons Sons (Stratford-upon-Avon, ( S t r a t f o r d - u p o n - A v o n , UK). UK). Suspending S u s p e n d i n g netting netting from the travelling irrigation irrigation booms booms (whilst (whilst irrigation irrigation is not not being being supplied), supplied), so that that the netting netting is dragged dragged backwards b a c k w a r d s and and forwards forwards over o v e r the plug plug trays trays on on the benches benches below, below, may may provide p r o v i d e a simple simple and and effective effective solution. solution.
Acknowledgements Acknowledgements The by Horticulture The authors authors gratefully gratefully acknowledge a c k n o w l e d g e the financial support support pprovided r o v i d e d by Horticulture Research Research International, International, the Horticultural Horticultural Development D e v e l o p m e n t Council, Council, East East Malling, Mailing, UK U K and and W.J. W.J. Findon Findon and and Sons, Sons, Stratford-upon-Avon, S t r a t f o r d - u p o n - A v o n , UK. U K . Particular Particular thanks thanks are also due due to Mr Mr Rodney R o d n e y Edmondson E d m o n d s o n and and a referee for assistance assistance with with statistical statistical analysis. analysis.
References References Autio, J.A., Voipio, I., Koivunen, T., 1994. 1994. Responses of aster, dusty miller, and petunia seedlings to daily 2), 1449-1452. exposure to mechanical stress. HortScience 29 (J (12), 14,19-1452. Beyl, C.A., Mitchel1, Mitchell, e.A., C.A., 1977. 1977. Characterization Characterization of mechanical stress dwarfing in chrysanthemum. chrysanthemum. J. Am. Soc. Hortic. Sci. 102 (5), (5), 591-594. 591-594. Biddington, N.L., 1986. plants-a review. Plant Growth Regul. 1986. The effects of mechanically-induced mechanically-induced stress in plants--a 4,103-123. 4, 103-123. Garner, L.C., Bjorkman, Bj~Srkman, T., 1996. 1996. Mechanical conditioning for controlling excessive elongation in tomato transplants: sensitivity to dose, frequency and timing of brushing. J. Am. Soc. Hortic. Sci. 121 121 (5), 894-900. 894-900. Garner, L.e., L.C., Langton. Langton, F.A., Bjorkman, Bjtirkman, T T.,.. 1997. 1997. Commercial adaptations of mechanical stimulation for tbr the control of transplant growth. Acta Hortic. 435, 219-230. 435,219-230. Heuchert, J.c., J.C., Mitchell, C.A., 1983. 1983. Inhibition of shoot growth in greenhouse-grown greenhouse-grown tomato by periodic gyratory shaking. J. Am. Soc. Hortic. Sci. 108 (5), 795-800. 795-800, Latimer, 1.G., J.G., 1991. 1991. Mechanical conditioning for control of growth and quality of vegetable transplants. HortScience HortScience 26, 1456-1461. 1456-1461. brush. Am. Veg. Grow. 40 (4), 62, 65, 68, 69. Latimer, J.G., 1992. 1992. For height control, give transplants the brush. MINITAB, 1995. 1995. Release 10 Xtra. Minitab Inc., State College, PA, USA. Mitchel1, Mitchell, C.A., Severson, C.J., Wott, J.A., Hammer, P.A., 1975. 1975. Seismomorphogenic Seismomorphogenic regulation of plant growth. growth, J. Am. Soc. Hortic. Sci. 100 (2), (2), 161-165. 161-165. Piszczek, P.M., Jerzy, M., 1987. 1987. The response of tomato (Lycopersicon (Lycopersicon esculentum MilL) Mill.) transplants to mechanical stress. Acta Agrobot. 40, 5-14. Wurr, D.C.E., Fellows, J.R., 1986. 1986. The influence of supplementary lighting and mechanically induced stress during plant raising, on transplant and maturity characteristics characteristics of crisp lettuce. J. Hortic. Sci. 61 61 (3), 325-330. 325-330.
**
Horticulture Research International, Wellesbourne, Wellesbourne, Wanvick, Wclrwick, CV35 CV35 9EF, 9EF, UK UK
Abstract Though brushing brushing is an effective method for controlling controlling excessive excessive elongation elongation in many species, its adoption by the commercial plug transplant transplant industry industry will depend on the ease and flexibility flexibility of its application, L.) seedlings growing at a density density of application. Brushing was applied to pansy (Viola tricolor L) ~ 2 by daily stroking with 20/20 1500 plants m m-2 20/20 gauge netting, netting. In dose response experiments, experiments, final final petiole length appeared to approach a lower asymptote asymptote as number number of brush strokes increased, and the number reduction in length increased under environmental number of strokes required to give near full full reduction environmental conditions conditions favouring favouring extension extension growth, growth. Ten or 20 daily strokes strokes, typically typically gave a 25-30% reduction reduction in petiole elongation elongation without causing plant damage or affecting subsequent subsequent flowering. flowering. Reductions Reductions in shoot dry weight tended to parallel those for petiole length. Increasing Increasing the interval interval between strokes by up to 10 min brushing. There was no rain resulted in similar reductions reductions as continuous continuous brushing. brushing 1 or 2 times difference between brushing brushing the plants at 09:00 or 16:00 h, or between brushing day ~ 1.I. Plants required at least 5 days treatment week week-- 1~ for significant significant size control. Brushing is an effective, effective, flexible flexible method for controlling controlling petiole length in pansy and it should find find application application in the commercial transplant transplant industry.
1. Introduction Introduction A difficulty faced by transplant growers is to produce plants of a specified size at the scheduled time. Control of bedding plant growth with chemical growth regulators is a common practice, but the use of these chemicals is expensive, difficult and increasingly increasingly restricted. Inexpensive, non-chemical methods of height control are needed which can be
easily adapted for commercial use. Mechanical stimulation (MS) can reduce stem and I). One type petiole elongation in a number of species (Biddington, (Biddington, 1986, 1986, Latimer, 199 1991). of MS, brushing, allows many plants to be stimulated at the same time. Brushing Brushing can significantly reduce petiole length in pansy (Viola tricolor L.) without causing plant damage (Gamer (Garner et aI., al., 1997), 1997), and there is the potential to use this technology in commercial operations if systems of brushing can be devised which are simple and flexible in their application. To this end, a series of experiments was conducted to determine the appropriate dosage and timing of brushing for pansy transplants and to characterise the daily amount, timing and number of days per week of brushing required for effective size control.
2. Materials Materials and methods 2.1. Plant culture Pansy seedlings ('Turbo Mix'), provided by W.J. Findon and Sons (Stratford-upon (Stratford-uponAvon, UK) were grown in 165 'plug trays' at a density densily of 1500 plants m -2. -2. Plants were maintained in a glasshouse at approximately ]8°C 18°C without supplementary lighting and 19: 19 (Vitax UK Limited. were watered and fertilised with Vitafeed 19: 19:19:19 Limited, Leicester, UK) as required. Plants were brushed by hand with a flexible 20/20 2 0 / 2 0 gauge netting (Bradley Lomas Electrolok, Ltd, Sheffield, UK), and each back and forth movement was counted as a single brush stroke. The netting was dragged carefully across the plant canopy to provide similar stem and petiole flexure with each stroke. MS was, therefore, provided by tactile stimulation of petioles and leaves, and by back and forth movement of entire shoots. Treatments were begun at the cotyledon stage of growth and continued continued until the plants were of a saleable size, typically after 25-30 25-30 clays days of treatment.
2.2. Dose response A previous experiment in which only three dosage levels of brushing were investi investigated showed that pansy petiole length could be significantly reduced by 10 or 20 brush strokes day - I1 without causing damage and without the large reductions in leaf area and shoot dry weight typically caused by 40 brush strokes day - Ii (Gamer (Garner et aI., al., 1997). 1997). Experiments were conducted, therefore, to examine more closely the relationship between the number of brush strokes per day and size reduction and, if possible, to determine an optimum dosage. Plants received 5, 10, 20, 30 or 40 brush strokes each morning, or were left untreated.
2.3. Interval between brush strokes Two experiments were conducted conducted to determine whether the time interval between brush strokes could be increased and still result in the same amount of height control as continuous brushing. The total daily stimulation remained constant, but the time interval between strokes was varied. Plants were either untreated, brushed continuously, or were
brushed with a 1- or 10-min l 0-min interval between paired back and forth strokes. A total of 20 brush strokes day day-- It were applied in the first experiment, and 10 or 20 strokes day - 1~ in the second experiment.
2.4. Time of of day Two experiments were conducted conducted to determine the most appropriate time of day for effective brushing. Plants were either untreated, or were brushed in the morning (at approximately 09:00 h), in the afternoon (at approximately 16:00 h) or twice a day (half in the morning and half in the afternoon). The total number of strokes was the same for each treatment (20 day-I day -~ in the first experiment, and 10 dayday -~I in the second experiment). 2.5. Times per week It would be commercially beneficial if transplants did not have to be brushed every day to maintain control of petiole elongation. Therefore, experiments were conducted conducted in which plants were either untreated or were brushed in the morning each day, 5 days a week (Monday to Friday, inclusive), or every other day. Twenty brush strokes day-I day- I in the second experiment. were applied in the first experiment and 10 strokes day day-~ 2,6. 2.6. Data collection and experimental design At the end of the treatment period, petiole length and shoot dry weight were measured, and any damage noted. Leaf area and the number of leaves per plant were also recorded in experiments concerning the time of day and the number of days per week of application. Experiments were typically conducted conducted using a randomised complete block design with six replications. However, a completely randomised design with four replications was used for dosage experiments. In all experiments, a quarter tray was used as the experimental unit, and ten plants from each plot were sampled for measurement. Guard rows one to two cells wide surrounded surrounded all experimental units, so that edge plants were not sampled. All the experiments were repeated in time. The first set of experi experiments was conducted conducted between 27 March and 2 May, 1996, 1996, and the second between 13 May and 10 June, 1996. 1996. During the second set of experiments, shade screens were used to prevent leaf damage on sunny days. Data were analysed using analysis of variance, the Chi-square test of homogeneity and Fisher's protected LSD with 95% confidence level (MINITAB, 1995), 1995),
3. Results Results 3,1. 3.1. Dose response In both experiments, the mean petiole length and mean shoot dry weight of brushed plants were significantly less than those of untreated plants (Table 1), l). There were no significant differences between the five brushing treatments for either variate in Experi Experi-
Table 11 Table The The effect effect of the the number number of brush brush strokes per day day on on the the growth growth of pansy pansy transplants transplants Brush strokes per per day Brush
Petiole Petiole length length (mm) (mm)
Shoot Shoot dry dry weight weight (mg)
Expt I1
Expt 2
Expt 11
None 5 10 10 20 30 40
12.8 12.8 10.0 9.3 9.6 10.1 10.1 9.8
20.2 2(I.2 17.4 1;'.4 15.0 14.0 13.3 13.3 12.8 12.8
59 52 50 51 51 45 50
vs untreated
untreated Brushed vs Linear trend
.
SE LSD LSD005 (18 d.f.) o05 (I8
NS
.
.
.
. * **
.
0.55 1.62 1.62
0,85 0.85 2.51 2.51
.
Expt 2 80 75 63 62 49 54
. NS
. * ~ *
4.1 4.1 -
4.1 4.1
12.3
12.3
NS. NS, '* •. . . . ., . ' • , ' , main effects within column not significant significant at P == 0.05 or significant significant at P < 0.001,0.01 0.001, 0.01 or
or respectively. Trends other than linear were non-significant non-significant at P == 0.05.
0.05. 0.05, respectively.
merit 1. However, H o w e v e r , in Experiment E x p e r i m e n t 2, a significant s i g n i f i c a n t linear l i n e a r trend t r e n d over o v e r the five brushing brushing ment treatments t r e a t m e n t s was w a s shown s h o w n (p ( P = 0.001), 0.001), with w i t h reductions r e d u c t i o n s in petiole petiole length l e n g t h and a n d shoot s h o o t dry w e i g h t as the number n u m b e r of o f brush b r u s h strokes strokes increased. increased. weight A l t h o u g h trends other o t h e r than linear l i n e a r were were formally f o r m a l l y non-significant n o n - s i g n i f i c a n t at P P = 0.05 0.05 in Although E x p e r i m e n t 2, visual inspection i n s p e c t i o n of o f the data data (Table ( T a b l e I) 1) suggested s u g g e s t e d that both b o t h height h e i g h t and and Experiment shoot s h o o t dry d r y weight w e i g h t approached a p p r o a c h e d a lower l o w e r limit l i m i t as the number n u m b e r of o f brush b r u s h strokes strokes increased. increased. This + b //(1 (! + + ex), cx), where where x = = number n u m b e r of of T h i s was w a s modelled m o d e l l e d by b y fitting the function f u n c t i o n yy = a + brush petiole b r u s h strokes, strokes, a a = the lower l o w e r asymptote a s y m p t o t e and and a a + + b = response r e s p o n s e when w h e n x = O. 0. For F o r petiole (see Fig. Fig. 1), this m model to the the ddata than did did the the llinear model llength e n g t h (see o d e l ggave a v e aa bbetter e t t e r fit to a t a than i n e a r ttrend rend m odel control). R Respective lack ooff m model for the the ttwo ((with w i t h uuntreated n t r e a t e d control). e s p e c t i v e lack o d e l fit sums s u m s ooff squares s q u a r e s for wo 2 m o d e l s were 1.640 m m 22 aand n d 9.451 m 2, oth w ith 3 3 d.f. s t i m a t e s ooff pparameters a r a m e t e r s were: , b models were 1.640 mm 9.451 m mm both with dJ. EEstimates were: mm mm); bb==9 . 9.21 mm (SE aa== 11.09 11.09 m m ((SE S E ==1 . 31.39 9 ram); 21 m m (SE ( S E == 1.44 1.44 rmm); a m ) ; ce==0 .0.1101 1101 ( S E == 0.0583). Similarly, was oobtained for the the aasymptotic model the linear linear 0.0583). Similarly, aa bbetter e t t e r fit was b t a i n e d for symptotic m o d e l tthan h a n the model for shoot dry weight, weight, w with lack ooff rresponse esponse m o d e l ((with w i t h uuntreated n t r e a t e d ccontrol) o n t r o l ) for s h o o t dry i t h rrespective e s p e c t i v e lack
22
20 ~ EEl8 v J~
SE~ SEi
16
B
._o 12
~- 10 8
i
o
~
o
i
i
i
o i
0 10 20 20 30 30 40 40 Number Number of of brush brush strokes strokes I. Relationships between numbers of brush strokes strokes and petiole petiole length in Experiment 1I (C)) (0) and Fig. 1. (.). Fitted curves are for the function 3' y= = a+ a + b/(lI+ + cx) ex) (see text). Experiment 2 (Q).
Ie
model fit sums of squares of 271.34 mg 22 and 428,10 428.10 mg 22 (dJ. (d.f. == 3). Estimates of parameters were: a = 37.8 mg (SE = 14.7 mg); rag); b = 43.2 mg (SE = 13.7 mg); c = 0.0530 (SE = = 0.0463). No such trend was apparent for Experiment 1, although it is possible that the response to brushing was essentially as in Experiment 2, but already approaching full expression after the application of five brush strokes. Fits to the asymptotic model (Fig. I) 1) and the linear response model (with untreated control) for petiole length were similar, m m 22 and 1.517 mm 22 with respective lack of model fit sums of squares of 1.590 mm (dJ. (d.f. == 3). Similar fits were also given to the two models for shoot dry weight, lack of (d.f, == 3). model fit sums of squares being 70.71 mg 22 and 80.70 mg 22,, respectively (dJ. Though 5 strokes day-I d a y - J did cause a statistically significant decrease in petiole length in Experiment 2 (a decrease in petiole length of about 14%) the stimulus was judged to be insufficient insufficient to be of practical importance to the grower. In both experiments, 30 or 40 brush strokes day-I d a y - f caused noticeable plant damage. interL,al between strokes 3.2. Time interval
In both experiments, brushing significantly significantly reduced petiole length, but there were no significant differences between the three brushing treatments (Table 2). Shoot dry weight was not significantly significantly affected by brushing and there was no noticeable damage in either experiment. More importantly, contrasts between continuous and non-continuous non-continuous brushing and between 1- and 10-min 10-rain intervals were not significant for any measured variate in either experiment. 3.3. Time of o f day Petiole length, leaf area and shoot dry weight were all significantly significantly decreased by brushing, though there were no significant differences between the three brushing
Table Table 2 The between paired paired brush brush strokes pansy transplants The effect effect of varying varying the the time time interval interval between strokes on on the the growth growth of pansy transplants Method brushing Method of brushing
Petiole Petiole length length(mm) (ram)
Shoot weight (mg) Shoot dry dry weight (mg)
Expt Expt 1l
Expt Expt 2
Expt 1l
Expt Expt 2
None None Continuous Continuous I-min l-min intervals intervals 10-rain intervals intervals 10-min
12.2 12.2 10.0 10.0 9.5 9.5 9.6
18.5 18.5 17.1 17.1 16.3 16.3 16.1 16.1
63 63 60 54 56 56
65 65 71 71 70 70 64
Brushed vs vs uuntreated ntreated Brushed Continuous Continuousvs vs non-continuous non-continuous 1- vs vs 10-min 10-minintervals intervals 1-
. NS NS NS NS
NS NS NS NS
NS NS NS NS NS NS
NS NS NS NS NS NS
0.47 0.47 1.57 1.57
0.92 0.92
SE SE LSD LSD005 (15 dJ.) d.f.) o05 (15
.
.
.
-
2.8 2.8
4.1 4.1
-
-
NS••" ,. .'. NS, . . .' , , '. main maineffects effects within within column column not not significant significantat P == 0.05 0.05 or significant significantat P < 0.001, 0.001, 0.01 0.01 or 0.05, respectively. 0.05, respectively.
Table 3 The effect of time of day of brushing on the growth of pansy transplants Petiole length (mm)
Leaf area (cm 22))
Shoot dry weight (mg)
Expt I1
Expt 2
Expt I1
Expt 2
Expt I1
None Morning and afternoon Morning only Afternoon only
15.4 12.0 12.8 12.3
18.6 16.6 16.1 15.6
12.35 10.56 10.31 t0.31 10.52
15.57 13.44 11.94 12.58
80 73 70 72
88 77 70 73
Brushed vs untreated I1 vs 2 applications day - Ii Morning vs afternoon
.
. NS NS
NS NS
Time and frequency of daily brushing
SE LSDo.o5 (J (155 d.f.) LSDoos
NS NS
.
.
. NS NS
0.45 l.l5 1.15
0.76 1.64
.
. . NS NS
.
0.530 l.l16 1.116
. . NS NS 0.738 2.328
3.5 -
Expt2 Expt 2
4.0 11.6 l 1.6
NS.••• NS, * . . . .,. •. , ., main effects within column not significant at P P = 0.05 or significant at P P < < 0.001, 0.01 or 0.05, respectively.
treatments t r e a t m e n t s for f o r any a n y of o f these t h e s e variates v a r i a t e s (Table ( T a b l e :3). 3). The T h e number n u m b e r of o f leaves l e a v e s per p e r plant p l a n t appeared appeared independent i n d e p e n d e n t of o f the t h e time t i m e of o f day d a y of o f bbrushing r u s h i n g in both b o t h experiments e x p e r i m e n t s (data ( d a t a not n o t shown) s h o w n ) and and there t h e r e was w a s no n o noticeable n o t i c e a b l e damage d a m a g e in either e i t h e r experiment. e x p e r i m e n t . Furthermore, F u r t h e r m o r e , contrasts c o n t r a s t s bbetween e t w e e n I1 and and 2 2 treatment t r e a t m e n t applications a p p l i c a t i o n s day d a y -1, - 1 , and a n d bbetween e t w e e n morning m o r n i n g and a n d evening e v e n i n g treatments, t r e a t m e n t s , were were n o t significant s i g n i f i c a n t for f o r any a n y measured m e a s u r e d variate v a r i a t e in either e i t h e r experiment. experiment. not 3.4. Times pper e r week week Treated T r e a t e d pplants l a n t s typically t y p i c a l l y had h a d significantly s i g n i f i c a n t l y shorter s h o r t e r ppetioles e t i o l e s than t h a n untreated u n t r e a t e d pplants l a n t s (Table (Table 4). 4). In I n Experiment E x p e r i m e n t I, 1, there t h e r e was was a a significant s i g n i f i c a n t nnegative e g a t i v e linear l i n e a r relationship r e l a t i o n s h i p bbetween e t w e e n ppetiole etiole length l e n g t h and a n d the t h e number n u m b e r of o f times t i m e s pper e r week w e e k that t h a t the t h e pplants l a n t s were w e r e treated. t r e a t e d . Brushing B r u s h i n g every every
Table 4 The effect of the frequency of brushing per week on the growth of pansy transplants Frequency of brushing
Petiole length (mm) (ram)
Leaf area (cm 22))
Shoot dry weight (mg)
Expt Il
Expt 2
Expt Il
Expt 2
None Alternate days per week 5 consecutive days week -I week-i 7 days week - Ii
12.4 11.5 I 1.5 10.4 9.6
16.8 15.4 14.4 14.2
9.28 8.34 7.80 7.06
13.38 12.04 10.63 11.73
65 61 S6 56 S3 53
80 75 68 7S 75
F test overall Brushed vs untreated trend a Linear trend"
" ** * ** **
NS NS NS
*~* *" * **
NS NS NS
** ~ ** " ,, x
NS NS NS
0.90 -
0.270 0.675
0.841 -
SE LSD LSDoo5 (155 dJ.) d.f.) oo5 (J
0.35 O.3S 1.06
Expt I1
2.1
2.1 4.0
Expt 2
4.2 -
"Based aBased on brushing 3.S, 3.5, 5 or 7 days week week-- Ii..
P< NS, ••• * . . . ., •• , main effects within column not significant at Pp,; := 0.05 or significant at P < 0.001 or 0.01,
0.01, respectively. There were no significant quadratic trends.
trends.
other other day day was was the the only only treatment treatment that that did did not not provide provide aa sufficient sufficient or or significant significant decrease decrease in petiole petiole length length relative relative to to unbrushed unbrushed plants. plants. A A similar similar trend trend was was noted noted for the the petiole petiole in length data data in in Experiment Experiment 2, 2, though though this this was was not not significant. significant. There There was was aa significant significant length negative relationship relationship between between both both the the leaf leaf area area and and shoot shoot dry dry weight weight and and the the number number of of negative times per per week week that that the the plants plants were brushed brushed in Experiment Experiment 1. 1, The The leaf leaf area area and and shoot shoot dry weight weight were were not not significantly significantly affected by any of of the the brushing brushing treatments treatments in Experiment 2. The The number number of of leaves per per plant plant seemed seemed independent independent of of the the brushing brushing Experiment treatments in both both experiments experiments (data (data not not shown). shown), There There was was no noticeable noticeable plant plant damage damage treatments in either either experiment. experiment.
4. Discussion Discussion 4. Environmental conditions conditions in experiments to detemfine detemline the the effects of of dosage were Environmental that petiole lengths lengths were substantially substantially greater in Experiment Experiment 2 (summer) than in such that Experiment 1 (spring). Under Under the conditions conditions of of Experiment Experiment 2, length length approached approached a lower lower Experiment limit with increasing number of strokes. A similar asymptotic response may have been shown in Experiment !I but but was missed because as few as five brush strokes invoked reduction. Whether Whether or not this is an accurate interpretation interpretation of of the near maximum reduction. brushing, it is apparent that numbers of biological response of pansy to stimulation by brushing, required to achieve full or near full growth reduction reduction are likely to be greater strokes required under conditions favouring extension growth than under conditions less favourable to growth. In practice, 10-20 10-20 brush strokes can be expected to give a commercially useful % reduction) at any time of year without causing plant damage, response (25-31 (25-31% damage. Associated reductions in shoot dry weight are likely to be of a similar or smaller percentage magnitude. In a previous experiment with tomato (Lycopersicon esculentum esculentum MilL) Mill.) transplants, the response r e s p o n s e to brushing b r u s h i n g was was also easily saturated saturated (Garner ( G a r n e r and Bjorkman, BjiSrkman, 1996), as it was with the pansy transplants in Experiment I. 1. Other re researchers have reported a negative relationship between the amount of stimulation given and the plant height of a number of species (Beyl and Mitchell, 1977, Heuchert and Mitchell, 1983, Autio et aI., al., 1994), and these results are similar to those obtained with the pansy transplants in Experiment 2. What is consistent among all of these experi experiments is that a relatively small amount of brushing brushing: can provide a significant and noticeable reduction in transplant size. Further brushing of the plants only increases the risk of damage and the effort associated with brushing, without substantially increasing the benefits of the treatment. Pansy plants which had been brushed continuously 20 times day - j),, 7 days week -)~,, were subsequently potted up in the greenhouse alongside control plants, and brushing was discontinued. This demonstrated that brushing had no adverse effect on flowering after transplanting; there was no delay in the appearance of flowers and no increase in the the number number of of days days to to 50% 50% flowering flowering (data (data not not: shown). shown). Brushing Brushing also also caused caused no no damage to to the the flowers. flowers. The The results of of the the experiments experiments on on increasing increasing the time interval interval between strokes strokes were consistent consistent with those of of aa similar similar experiment experiment using tomato transplants (Garner (Garner and and Bjorkman, Bj6rkman, 1996), 1996). For For both species, species, the time interval interval between strokes strokes can can be at at least least 10 10
min long, and still result in similar size control as continuous stimulation. It is not necessary for pansy plants to receive daily brushing in a series of continuous strokes. This provides flexibility for commercial application, especially if the technique is to be automated. The effectiveness of brushing was not significantly influenced by the time of day of its application. The response of tomato plants to MS is also typically unaffected by the time of day of treatment application (Heuchert and Mitchell, 1983, 1983, Gamer Garner and Bjorkman, BjSrkman, 1996), 1996), though chrysanthemums (Dendranthema (Dendranthema X × grandiflorum (Ramat.) Kitam.) are slightly more sensitive to MS in the morning (Beyl and Mitchell, 1977). 1977). Results from the pansy experiments, however, are nOll no~t consistent with research showing that tomato plant height is more greatly reduced by two or more small daily vibration treatments than by one daily equivalent treatment (Mitchell et aI., al., 1975, Piszczek and Jerzy, 1987). 1987). This difference between the response of tomato and pansy plants could be real, but it might also reflect, in part, the increased amount of handling required to place the tomato plants on a gyratory shaker several times each ,each day. In commercial practice, the timing of brushing pansy transplants should be extremely flexible. There were no statistical differences between treating the plants once each day (20 or 10 strokes) or twice each day (ten or five strokes), or between treating them in the morning or the afternoon. The choice of the best time of day for brushing can be left to the individual grower, and could even be determined on a daily basis to minimise interference with production practices and to avoid brushing the plants when they are either wilting or wet. The results of experiments on the number of treatments per week were consistent with previous research in which decreasing the number of days per week on which lettuce (Latuca satiea sativa L.) transplants were brushed decreased the effectiveness of treatment (Wurr and Fellows, 1986). 1986). However, for both lettuce and pansy transplants, some reduction in the frequency of brushing can be tolerated. In Experiment I, 1, brushing for only 5 days week -~I provided a significant decrease in petiole length while minimising reductions in leaf area and shoot dry weight. Whilst brushing at least Ii time day-l d a y - ~ has been recommended for the height control of tomato and cucumber (Cucumis sativus L.) transplants (Latimer, 1992), 1992), this does not appear to be necessary for pansy transplants. It is concluded that brushing is a sufficiently flexible technique to be integrated with commercial production practices. Pansy transplants require only a small amount of daily stimulation to achieve maximum growth reduction, and the dosage can be adjusted to suit the growth rate of the crop. It is likely that the degree ,degree of growth control achieved with 10-20 10-20 brush strokes day-I day- ~ will fully satisfy commercial requirements in the spring and autumn periods when the extension growth of pansy is naturally limited, but some additional control by the use of chemical growth regulators may be required in the more difficult summer period. However, brushing will greatly reduce the numbers of growth regulator applications needed or the concentrations required. The timing of the stimula stimulation is not critical. Plants can be brushed at a time when the grower finds it most convenient, and brushing does not have to be applied continuously. ,continuously. Plants do not have to week-I is likely to be be brushed every day, although treatment on at least 5 days week-~ necessary for effective size control. The response of plants to MS varies with species,
but this and but and other other work w o r k consistently consistently show s h o w that that the magnitude m a g n i t u d e of of the response response to MS M S is not by altering not greatly greatly affected affected by altering the dosage dosage or or timing tinting of of the stimulation. stimulation. Some S o m e form f o r m of of mechanisation m e c h a n i s a t i o n is essential essential in order order to exploit exploit the utility of o f brushing brushing in commercial practice, and c o m m e r c i a l practice, and trials to achieve a c h i e v e this have have begun b e g u n at W.J. W.J. Findon Findon and and Sons Sons (Stratford-upon-Avon, ( S t r a t f o r d - u p o n - A v o n , UK). UK). Suspending S u s p e n d i n g netting netting from the travelling irrigation irrigation booms booms (whilst (whilst irrigation irrigation is not not being being supplied), supplied), so that that the netting netting is dragged dragged backwards b a c k w a r d s and and forwards forwards over o v e r the plug plug trays trays on on the benches benches below, below, may may provide p r o v i d e a simple simple and and effective effective solution. solution.
Acknowledgements Acknowledgements The by Horticulture The authors authors gratefully gratefully acknowledge a c k n o w l e d g e the financial support support pprovided r o v i d e d by Horticulture Research Research International, International, the Horticultural Horticultural Development D e v e l o p m e n t Council, Council, East East Malling, Mailing, UK U K and and W.J. W.J. Findon Findon and and Sons, Sons, Stratford-upon-Avon, S t r a t f o r d - u p o n - A v o n , UK. U K . Particular Particular thanks thanks are also due due to Mr Mr Rodney R o d n e y Edmondson E d m o n d s o n and and a referee for assistance assistance with with statistical statistical analysis. analysis.
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