Use of Bioregulators to Control Vegetative Growth ... - ACS Publications

9 Use of Bioregulators to Control Vegetative Growth of Fruit Trees and Improve Fruiting Efficiency

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M A X W. WILLIAMS Tree Fruit Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Wenatchee, WA 98801

The growth retardant paclobutrazol was applied to the soil at the base of 'Delicious' and 'Golden Delicious' apple trees. One application per tree in 1979 controlled terminal shoot growth for several seasons. There was little or no e f f e c t of the chemical on f r u i t s i z e . Y i e l d increased on treated trees and the f r u i t colored e a r l i e r because of the increased sunlight on the f r u i t i n g spurs. The high rates of paclobutrazol caused no phytotoxicity but had an adverse e f f e c t on 'Delicious' f r u i t shape and stem length. A complete reversal of the adverse effects was obtained by applying Promalin at 25 ppm. Promalin contains equal amounts of GA and 6-BenzylAdenine. By reducing excessive terminal growth, tree e f f i c i e n c y is increased. 4+7

Many plants produce more leaves than are needed for maximum photosynthesis, and the shade from one or two leaves markedly reduces photosynthesis in the shaded leaves (1). The control of excessive shoot growth and shading in f r u i t trees is a major concern of f r u i t growers. Many forms of dormant and summer pruning are used to allow more sunlight into the trees to increase f r u i t f u l n e s s and improve f r u i t q u a l i t y . Dwarfing rootstocks are also used to improve the manageability of f r u i t trees, but the proper choice of rootstock/scion combination for each soil is difficult. Optimum l e v e l s of f e r t i l i z e r are important to give a proper balance between vegetative growth, f r u i t load and return bloom. C u l t u r a l practices such as limb spreading or tying are useful to retard vigorous upright growth and increase spur development but are expensive and generally limited to t r a i n i n g of young trees. As trees get older heavy dense canopies shade lower portions of the tree and r e s u l t in low vigor spurs with i n f e r i o r flowers and f r u i t , and growers are at a loss to know how to manage the trees. These problems have plagued f r u i t growers since the

This chapter not subject to U.S. copyright. Published 1984, American Chemical Society

Ory and Rittig; Bioregulators ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

BIOREGULATORS: CHEMISTRY AND USES


94

beginning of domestic f r u i t culture, and plant breeders have yet to solve the problem. The f i r s t attempt to control the vegetative growth of f r u i t trees with chemicals was reported in 1963 by Batjer, Williams and Martin (2). The chemical used was referred to as B-9, which l a t e r was given the common name daminozide, and the trade name: Alar. Some excellent uses have been developed f o r daminozide, such as increasing spur development, flowering, f r u i t set, red color and firmness of the f r u i t (3,4). These benefits are a l l obtained with moderate rates of daminozide. However, very high rates of damino zide are necessary to achieve s a t i s f a c t o r y control of shoot growth and these high rates result in excessive reduction of f r u i t s i z e . A new compound shown in Figure 1 [1,(4-chlorophenyl)-4, 4-dimethyl-2(l,2,3-triazol-l-yl)pentan-3-01] (ICI PP333) which has the common name paclobutrazol shows considerable promise f o r con t r o l l i n g excess shoot growth without seriously reducing f r u i t size or quality (5-8) . /=Ξ\

(CH^gC Figure 1.

A new chemical compound, paclobutrazol.

Methods, Results and Discussion In the spring (May) of 1979 trees of 'Spur Delicious' on seedling roots and trees of 'Golden D e l i c i o u s ' on M7 roots were sprayed with 1000 or 2000 ppm of paclobutrazol. Only about 10-20% reduction in growth occurred the year of spraying. The following season 80-90% control of shoot growth was achieved. The trees were sprayed to run off with high pressure handguns and a considerable amount of spray dripped from the foliage onto the soil under the trees. The spray material used per tree contained an equivalent of 0.5 g AI of paclobutrazol per M for the 1000 ppm spray and 1.0 g AI per M for the 2000 ppm spray. The major increase in response obtained the second year a f t e r spraying was related to the amount of chemical dripped onto the ground under the trees. In the f a l l of 1979, 0.25, 0.5, 1.0 and 2.0 g AI per M rates of paclobutrazol were applied d i r e c t l y to a 10 sq M area of sandy loam soil around the base of vigorous 25-year-old trees of 'Spur D e l i c i o u s on seedling roots, and 'Golden D e l i c i o u s ' on M7 roots. Three trees of each c u l t i v a r were treated with each rate of paclobutrazol. In 1980 only minor growth control occurred, in 1981 the f u l l effect of treatment was manifested. The amount of growth control ranged from 10 to 90% (Table I ) . Treatments at the higher rates increased f r u i t set and f i n a l y i e l d without reducing f r u i t size (Table I ) . Part of the increase in y i e l d on treated trees was due to an increase in resistance to frost imparted by paclobutrazol. Spring f r o s t s occurred in the test block in 1981 and in 1982. No hand or chemical thinning was done in 1981, thus the smaller crop loads that resulted in 1982 (Table I ) . Some low vigor limbs on the treated 'Spur Delicious' trees bore flattened f r u i t with short stems. The l a t t e r was e s p e c i a l l y true at the 2

2

2

1


9.

95

Applications on Fruit Trees

WILLIAMS

higher rates of paclobutrazol. F r u i t quality determinations such as firmness, a c i d i t y and soluble s o l i d s were made on samples from treated and control trees. The treatments had no s i g n i f i c a n t affect on the quality parameters measured (Table I I ) . Quality tests on f r u i t treated in 1982 v e r i f i e d the 1981 data (not shown). Without any renewal treatment, the control of shoot growth in 1983 was nearly 100% from the 2 g per M concentration applied in the f a l l of 1979. 2


Table I.

Effect of Ground Application of Paclobutrazol Made in F a l l of 1979 on Growth Measured in 1981

Treatment

Check 0.25 0.50 1.00 2.00

Fruit weight (8)

8

166 185 174 186 179

2

g/M g/M g/M g/M

2

2

2

Yield 1981 1982 (35// boxes)

Terminal shoot Fruit growth firmness (% of growth) (lbs) Red Delicious 15.51 15.44 15.16 15.08 15.42

100 95 80 40 10

7.1 7.5 10.4 12.5 15.4

4.9 5.6 7.9 8.3 6.9

100 95 85 40 10

14.6 7.1 14.6 18.8 20.8

4.6 6.5 6.5 5.6 3.5

Golden Delicious Check 0.25 0.50 1.00 2.00

204 202 210 209 220

2

g/M g/M g/M Ç/M

2

2

2

M e a s u r e m e n t s made on

10.86 10.97 10.88 10.07 11.26 20

fruit

and

10

shoots per

tree.

In a separate t r i a l in 1980, three vigorous 25-year-old trees of 'Top Red Delicious' on seedling roots planted 20' χ 20' were treated by applying paclobutrazol at a rate of 1.0 g per M in a band 2-feet wide just inside the outer edge of the tree canopy. The t o t a l area treated per tree equaled 15 M . Again the f i r s t year after treatment little or no reduction in growth occurred. However, in 1982, 90% control of shoot growth was achieved. The f r u i t were harvested from the treated and adjacent control trees and graded on a commercial f r u i t packing l i n e . There were 10% more Extra Fancy f r u i t , because of the increased red color, and 41% more f r u i t of size 100 and larger from the treated trees. The percentages of c u l l f r u i t were 0.06 and 0.14, respectively, for the treated and control f r u i t . Trees of 'Granny Smith' on M26 roots in t h e i r 6th leaf were treated using ground applications of paclobutrazol. The 0.25 g and 0.5 g per M rate applied to an area of 1 M around the trunk gave adequate growth control without seriously a f f e c t i n g f r u i t size (data not shown). The 1.0 and 2.0 g/M rates on a l l c u l t i v a r s 2

2

2

2

2



3

166 185 174 186 179

204 202 210 209 220

100 95 80 40 10

100 95 85 40 10

3.68 3.48 3.66 3.62 3.50

22.47 22.96 22.66 23.35 23.06 Golden Delicious 12.0 24.71 11.6 24.58 12.0 25.18 11.8 25.25 12.0 25.61

ΡΗ

3.98 3.93 3.82 3.95 3.95

Delicious

Soluble solids (%)

10.4 11.0 11.4 11.0 11.4

Red

Fruit size circ. (cm)

Measurements made on 20 f r u i t or 10 shoots per tree.

2

2

2

2

Checks 0.25 g/M 0.50 g/M 1.00 g/M 2.00 g/M

2

2

2

2

Checks 0.25 g/M 0.50 g/M 1.00 g/M 2.00 g/M

Treatment

Fruit weight (g)

0.368 0.372 0.354 0.328 0.317

0.182 0.193 0.182 0.179 0.179

Malic acid (%)

10.86 10.97 10.88 10.07 11.26

15.51 15.44 15.16 15.08 15.42

Fruit firmness (lbs)

E f f e c t of Paclobutrazol F a l l Ground Application in 1979 on Growth and Quality Measurements of Apples in 1981

Vegetative growth (% of check)

Table I I .


0.98 1.00 0.97 0.91 0.97

1.03 1.07 1.06 1.04 1.02

Shape L/D ratio


9. W I L L I A M S

97


tested were excessive treatments, e s p e c i a l l y when applied to trees on dwarfing rootstocks or to trees in a low state of vigor. The f l a t f r u i t and short stem e f f e c t s of paclobutrazol on apple were reversed with applications of cytokinin and g i b b e r e l l i n s at bloom time (9). The cytokinin application on apples also increased leaf size (Table I I I ) . The results were s a t i s f a c t o r y when only a moderate amount of reversal was needed. With 'Spur Red Delicious' 50-70% control of shoot growth may be the i d e a l amount of vegetative growth control to achieve to avoid any adverse f r u i t shape problem. With standard nonspur trees like 'Top Red Delicious', 'Golden Delicious' and 'Granny Smith', i t is possible to achieve adequate control of shoot growth without seriously a f f e c t i n g f r u i t shape. Table IV indicates the e f f e c t of paclo butrazol treatments followed by the application of Promalin on f r u i t shape expressed as length to diameter r a t i o s .

Table I I I . Average Area and Weight of Spur Leaves from 'Delicious' and 'Granny Smith' Apple Trees Treated With paclobutrazol and Promalin, 1983

Treatment Control PP333 20g AI PP333 + Promalin a

Spur Delicious Leaves Area Weight (cm ) (g) 2

a

23 24 33

Granny Smith Leaves Area Weight (cm ) (g) 2

0.8 0.8 1.2

44 34 56

0.5 0.7 0.9

25 largest spur leaves per tree, 3 trees per treatment.

Table IV. F r u i t L/D Ratios of 'Delicious' , 'Golden Delicious', and 'Granny Smith' Apple Trees Treated with Paclobutrazol and Promalin, 1983 Treatment Control PP333 20g AI PP333 + Promalin

Delicious

Golden Delicious

0.95 0.89 1.16

0.93 0.96 1.06

Granny Smith 0.92 0.88 1.03

'D'Anjou' pear trees with low, medium and high nitrogen (N) levels were treated with 2.0 g/M of paclobutrazol. Six trees per treatment were observed f o r number of f r u i t set, insect damage, and o v e r a l l f r u i t quality. The number of f r u i t per tree f o r the control, low Ν + PP333, medium Ν + PP333 and high Ν + PP333 treatments was 275, 414, 409, 497, respectively. F r u i t f i n i s h was improved with treatment and less mite and p s y l l a damage occurred. The results on insect damage and physiological disorders are reported elsewhere by Raese and Burts (10). F r u i t size was s l i g h t l y smaller on treated pear trees because of the s i g n i f i c a n t increase in f r u i t load. F r u i t shape and stem 2



98

BIOREGULATORS: CHEMISTRY A N D USES

length were affected by the high rates of paclobutrazol. The stems were short and the f r u i t were more compact. With shorter stems there was less stem puncture damage. At the more moderate application rates f r u i t shape and stem length were less affected. Because of the increase in f r u i t set and the reduced amount of foliage on 'Anjou* pears, a 25 ppm g i b b e r e l l i c acid (GA ) spray was applied to limb units on d i f f e r e n t trees at petal f a l l and at 4 weeks a f t e r f u l l bloom in an attempt to increase leaf and f r u i t size. The petal f a l l spray increased leaf size by about 20% but did not affect f r u i t s i z e . The l a t e r GA spray at 4 weeks a f t e r bloom increased leaf size by about l u % and f r u i t size was dramatically increased. F r u i t shape was not affected by the GA^ spray applied at 4 weeks a f t e r bloom. The use of paclobutrazol to reduce excess shoot growth followed by GA^ to increase f r u i t size greatly increased the f r u i t i n g e f f i c i e n c y of 'Anjou' pear trees (Table V).

Table V.

Effect of 1980 F a l l Treatment with Paclobutrazol at 20 g AI/100 Square Feet on 'Anjou' Pear F r u i t Size and Volume Measured in 1982

3

Treatment Control PP333 PP333 + 25 ppm GA

Fruit circumference 17.3 16.6 20.0

Fruit volume 87.9 77.3 135.1

Volume of fruit/cm limb x-section 104 156 294 2

GA« applied 4 weeks after f u l l bloom, 1982.

Conclusions The a b i l i t y to control excessive shoot growth on apple and pear trees will be of considerable benefit to the f r u i t industry. Some of the benefits are: (1) less pruning required; (2) increased f r u i t set; (3) easier control of insects and diseases; (4) stronger spurs in lower h a l f of trees because of increased exposure to l i g h t ; (5) higher pack out of Extra Fancy red c u l t i v a r s of apples because of more exposure to l i g h t ; (6) easier harvesting with fewer limb rubs and handling bruises; and (7) higher pack out on 'Anjou' pears because of fewer stem punctures, limb rubs and handling bruises. The mode of action of paclobutrazol is in the i n h i b i t i o n of the synthesis of g i b b e r e l l i n s (GA) (11). GA promotes shoot growth in most plant species. By i n h i b i t i n g the natural production of GA and adding GA back to the plant i t is possible to have complete control of vegetative growth and f r u i t i n g . With some f r u i t species such as pear, cherry and peach, i t is possible to increase the volume of f r u i t by more than 100% by treating with paclobutrazol to control excessive vegetation growth, followed by an application of GA or GA plus cytokinins to increase leaf and f r u i t s i z e . These


9.

WILLIAMS


99

techniques have great potential f o r increasing the productivity of many h o r t i c u l t u r a l crops. Literature Cited


1. 2.

Heinicke, Don. R. Proc. Amer. Soc. Hort. S c i . 1966, 88, 1-8. Batjer, L. P.; Williams, M. W.; Martin G. C. Proc. Wash. State Hort. Assoc. 1963, 59, 105. 3. Williams, M. W.; Batjer, L. P.; Martin, G. Proc. Amer. Soc. Hort. S c i . 1964, 85, 17-9. 4. Bartram, R. D.; Olsen, K. L.; Williams M. W. HortScience 1971, 6, 240-1. 5. Williams, M. W. Proc. PGR Society of America. 1982. 6. Quinlan, J. D.; Webster, A. D. XXIst International Horticulture Congress, Hamburg, Germany, 1982, 2, 1071. 7. Quinlan, J. D.; Webster, A. D. XXIst International Horticulture Congress, Hamburg, Germany, 1982, 1, 1285. 8. Williams, M. W.; Edgerton, L. J. Acta Horticulturae 137, Growth Regulators, 1983. 9. Curry, Ε. Α.; Williams, M. W. HortScience 1983, 18, 214-5. 10. Raese, J. Thomas; Burts, E. C. HortScience 1982, 18, 212-4. 11. Hedden, P., unpublished.

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February 22, 1984


Use of Bioregulators to Control Vegetative Growth ... - ACS Publications

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