Reproductive growth regulation of apples with mefluidide

Scientia Horticulturae, 34 (1988) 13-19 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

13

Reproductive Growth Regulation of Apples with Mefluidide M.R. WARMUND

Department o/Horticulture, University o/Missouri, Columbia, MO 65211 (U.S.A.) (Accepted for publication 18 May 1987 )

ABSTRACT Warmund, M.R., 1988. Reproductive growth regulation of apples with mefluidide. Scientia Hortic., 34: 13-19. Mefluidide was applied at 5 g l - ' to 'Empire' and 'Miller SturdySpur Delicious' trees at full bloom (FB) and 15 days after full bloom (FB + 15) in 1985 to evaluate its efficacy as a thinning agent. In a similar experiment, 'Starkspur Golden Delicious' trees were treated with naphthaleneacetic acid (NAA) at 0.02 g l - ' at 7 days after full bloom (FB + 7 ) or mefluidide at 2.5 and 5.0 g l- ' at FB, FB ÷ 7 and FB ÷ 15. Fruit set was not reduced, but fruit number at harvest and quality were affected by mefluidide treatments. 'Empire' and 'Miller SturdySpur Delicious' fruit treated with mefluidide had greater flesh firmness than untreated fruit, but did not differ in soluble solids. Mefluidide at 2.5 g l - ' applied FB ÷ 7 to 'Starkspur Golden Delicious' trees delayed maturity and reduced fruit weight, yield and length/diameter (L/D) ratios. Fruit treated with mefluidide at FB ÷ 7 and FB ÷ 15 were firmer than untreated controls. Apples treated with NAA also had softer flesh than those treated with mefluidide at FB ÷ 7. NAA-treated trees had greater average fruit weight at harvest and return bloom the following year than mefluidide-treated trees. Keywords: fruit quality; fruit set; Malus domestica Borkh.; naphthaleneacetic acid; thinning. Abbreviations:FB = full bloom; FB ÷ 7 = 7 days after full bloom; FB + 15 = 15 days after full bloom; L/D ratio = length/diameter ratio; NAA = naphthaleneacetic acid.

INTRODUCTION

Mefluidide ( N- [2,4-dimethyl-5- [ [ (trifluoromethyl) sulfonyl] amino] phenyl] acetamide) is a plant growth regulator used to suppress vegetative growth of turfgrasses and woody ornamentals (Jagschitz, 1975; Watschke, 1976; Parups and Cordukes, 1977; Schmidt and Bingham, 1977; Cohen, 1978; Campbell, 1983; Dernoeden, 1984). Although the exact mode of action of mefluidide has not been elucidated, several researchers have suggested that it affects biosynthesis of gibberellins and thereby inhibits cell division and elongation (Field and Whitford, 1982; Tautvydas, 1983; Fales and Wilkinson, 1984). Wilkinson 0304-4238/88/$03.50

© 1988 Elsevier Science Publishers B.V.

14 (1982) reported that 0.01 ~M mefluidide inhibited synthesis of the gibberellic acid precursor, ent-kaurenol in sorghum (Sorghum bicolor L.) by 80%. However, Truelove et al. (1977) found that gibberellic acid applications did not reverse the growth-retarding effects of mefluidide in corn. Mefluidide also alters the reproductive growth of plants. Mefluidide is currently labeled to remove flowers on ornamental olive (Elaeagnus sp.) trees when applied from pre-bloom to 5% bloom. Woodson and Raiford (1986) reported that mefluidide delayed flowering of Hibiscus rosa-sinensis L. Bloom, fruit weight and yield of peach (Prunus persica ( L. ) Batsch ) were reduced by mefluidide at 1.9, 3.7 and 5.6 g l-1 the year following treatment (Arnold et al., 1981). Since mefluidide has reduced flowering or fruit set in diverse woody species, including stone fruit, it may cause a similar effect on pome fruit. Thus, the purpose of this study was to determine if mefluidide could be used to reduce fruit set on apple trees without an adverse effect on fruit quality. MATERIALSAND METHODS Mefluidide was applied at 5 g 1-1 to 10-year-old 'Empire' and 'Miller SturdySpur Delicious'/Malling-Merton 111 (MM 111 ) trees at full bloom (FB) and FB + 15 in 1985. Thirteen-year-old 'Starkspur Golden Delicious'/MM 111 trees were also treated with mefluidide at 2.5 and 5.0 g 1-1 at FB, F B + 7 and FB + 15. NAA at 0.02 g 1-1 applied at FB + 7 was also included in this experiment as a standard treatment of comparison. Treatments were applied with a hand-gun delivering approximately 19 1 per tree at 2415 kPa. A randomized complete block design was used with 3 replications of each treatment of 'Empire' and 'Miller SturdySpur Delicious' trees and 5 replications of each treatment of 'Starkspur Golden Delicious' trees. Four uniform limbs per tree were selected to determine fruit set after June drop. Ten apples per tree were randomly selected for fresh weight determinations on 16 May and 26 June. At harvest, fruit number and total yield were obtained and 100 apples per tree were used for fruit weight determinations. Twenty of these apples were sub-sampled for fruit quality evaluations including L/D ratios, flesh firmness, soluble solids and fruit color. A color difference meter (Model D25D2A, HunterLab, Fairfax, VA) was used to quantify fruit color. On the meter, "L" measured darkness from 0 (black) to 100 (white), "a" quantified redness and "b" measured yellowness of the apple. Return bloom was visually rated on a scale of 0 (no bloom) to 10 (100% bloom) on 8 April 1986. Data were subjected to an analysis of variance and means were separated by a least significant difference (LSD) test. Orthogonal contrasts were performed on data from 'Starkspur Golden Delicious' trees to test the effect of different dates of application on fruit weight, yield and quality parameters.

15 TABLE I Effect of mefluidide on fruit set in 1985 a n d return bloom in 1986 on 'Starkspur Golden Delicious' trees 1 Treatment

Rate ( g l 1)

Date of application (days after full bloom)

Fruit set (%)

R e t u r n bloom (%)

Mefluidide Mefluidide Mefluidide Mefluidide Mefluidide Mefluidide NAA U n t r e a t e d control

2.50 2.50 2.50 5.00 5.00 5.00 0.02 -

0 7 15 0 7 15 7 -

75 71 73 75 72 74 30 71

0 10 10 0 10 10 50 0

17

20

LSD (5%) ~Mean separation by LSD. RESULTS

Bloom was heavy in 1985 on all trees. NAA was the only treatment that reduced fruit set in 1985 and these trees had greater than 10% bloom in 1986 ( Table I ). Mefluidide treatments did not reduce fruit set in 1985 and resulted in a poor return bloom in 1986 (data not shown for 'Empire' and 'Miller SturdySpur Delicious'). Although mefluidide did not effectively thin fruit, it did affect fruit weight, quality, maturity and the number of apples at harvest. In May, terminal growth of mefluidide-treated trees exhibited foliar injury and the calyx ends of apples were misshapen, but the fruit and foliage remained on the trees and by July appeared undamaged. Although measurements were not obtained, it appeared that greater force was required to harvest the apples from mefluidide-treated trees, and this resulted in more spur damage in those trees than in untreated trees. Mefluidide at 5 g l- 1 applied at FB reduced the weight of 'Miller SturdySpur' apples on 16 May (Table II ). Trees treated with the growth regulator at FB + 15 had reduced fruit weight on 26 June, but the weight of apples from mefluididetreated trees was not significantly different from that of untreated trees at harvest ( 5 September). Fruit number at harvest was increased with mefluidide at F B + 15, but was reduced by the treatment at FB when compared to the untreated controls. Yield was reduced on trees that had received the mefluidide treatment at FB as compared to that of untreated trees. Apples from untreated trees had softer flesh and greater L/D ratios than those from mefluidide-treated trees, but the soluble solids were not affected by mefluidide. Apples from untreated trees were darker in color (L value) than those from mefluidide-treated trees.

Date of application (days after full bloom)

0 15 10

89 100 110

19

60 78 96

16 May

56

509 422 612

109

486 385 567

26 J u n e

Wt./10 fruit (g)

NS

12 11 13

NS

17 14 18

Wt./100 fruit (kg) 5 Sept.

400

844 1482 1043

223

514 1134 894

F r u i t no. at harvest

NS

108 173 137

64

87 147 157

Yield (kg)

0.02

0.81 0.84 0.84

0.01

0.82 0.85 0.90

L/D ratio

7.8

81.4 85.3 71.6

4.9

77.5 75.5 62.8

Flesh firmness (N)

NS

13.3 12.9 12.4

NS

12.1 11.3 12.0

Soluble solids ( ° brix)

1.5

24.4 28.7 23.5

0.7

26.7 32.3 25.5

L

NS

28.6 28.5 31.1

NS

29.7 25.0 28.5

a

F r u i t color 2

1Mean separation by LSD. N S = not significant. 2Fruit color was measured on a color difference m e t e r where L, a a n d b quantified darkness, redness a n d yellowness of the apple, respectively.

LSD (5%)

'Empire' Mefluidide Mefluidide U n t r e a t e d control

LSD (5%)

'Miller SturdySpur Delicious' Mefluidide 0 Mefluidide 15 U n t r e a t e d control -

Treatment

Effect of mefluidide at 5 g l - 1 on fresh weight, yield a n d quality of 'Miller S t u r d y S p u r Delicious' a n d ' E m p i r e ' apples ~

T A B L E II

0.4

8.5 9.9 7.9

NS

9.7 9.9 8.6

b

17 TABLE III Effect of rate and date of application of mefluidide on fresh weight and yield of 'Starkspur Golden Delicious' apples' Treatment

Rate (g l- 1)

Date of Wt./10 fruit (g) Wt./100 fruit Fruit no. Yield application (kg) at harvest (kg) (days after 16 May 26 June 5 Sept. full bloom )

Mefluidide Mefluidide Mefluidide Mefluidide Mefluidide Mefluidide NAA Untreated control

2.50 2.50 2.50 5.00 5.00 5.00 0.02 -

0 7 15 0 7 15 7

65 53 68 62 39 76 75 88

457 368 406 418 212 427 611 585

12 10 11 12 7 11 16 16

2281 1467 1891 2332 3204 2634 1110 1605

266 174 204 265 222 275 188 247

LSD (5%)

11

79

3

712

100

Significant effects2'3 Rate DateL DateQ Rate X dateL Rate X dateQ

NS * ** NS *

* NS ** NS **

NS NS ** NS *

** NS NS NS NS

NS NS NS NS NS

1Means of the mefluidide treatments, NAA and the untreated control were separated by LSD. 2Linear and quadratic orthogonal contrasts were performed to test the trend of different rates and dates of application {date) ofmefluidide. 3NS, not significant; *, 5% level; **, 1% level; L, linear; Q, quadratic. F r u i t w e i g h t of ' E m p i r e ' t r e e s s a m p l e d on 16 M a y a n d 26 J u n e w a s r e d u c e d b y t h e m e f l u i d i d e t r e a t m e n t s . Average fruit w e i g h t a t h a r v e s t , yield a n d soluble solids of m e f l u i d i d e - t r e a t e d t r e e s were n o t s i g n i f i c a n t l y d i f f e r e n t f r o m t h o s e of u n t r e a t e d trees. T r e e s t r e a t e d w i t h m e f l u i d i d e at F B + 15 h a d a g r e a t e r fruit n u m b e r a t h a r v e s t t h a n t h o s e t r e a t e d a t F B or t h e u n t r e a t e d controls. F l e s h f i r m n e s s a n d t h e yellow color (b v a l u e ) o f f r u i t f r o m m e f l u i d i d e - t r e a t e d t r e e s was g r e a t e r t h a n t h o s e o f f r u i t f r o m u n t r e a t e d trees. F r u i t w e i g h t of m e f l u i d i d e - t r e a t e d ' S t a r k s p u r G o l d e n Delicious' t r e e s was reduced, c o m p a r e d to t h a t of u n t r e a t e d trees, a n d e x h i b i t e d a q u a d r a t i c res p o n s e to t h e i n t e r a c t i o n of m e f l u i d i d e r a t e a n d d a t e of a p p l i c a t i o n at all 3 s a m p l i n g d a t e s ( T a b l e I I I ) . F r u i t n u m b e r at h a r v e s t was i n c r e a s e d b y mefluidide a t 5 g 1-1 as c o m p a r e d to t h e u n t r e a t e d control. Yield f r o m ' S t a r k s p u r G o l d e n Delicious' t r e e s t r e a t e d w i t h m e f l u i d i d e at 2.5 g l - 1 a t F B + 7 was sign i f i c a n t l y lower t h a n t h a t of t r e e s t r e a t e d w i t h t h e g r o w t h r e g u l a t o r a t 5.0 g l - 1 at F B + 15. M e f l u i d i d e a p p l i e d a t F B a n d F B + 7 r e d u c e d t h e L / D r a t i o s of

18 TABLE IV Effect of rate and date of application of mefluidide on the quality of'Starkspur Golden Delicious' apples ~

Treatment

Rate

Fruit color

(N)

Soluble solids ( o brix)

L

a

b

Untreated control

0.86 0.82 0.89 0.83 0.83 0.90 0.90 0.91

67.7 82.4 70.8 68.6 98.1 71.6 66.7 63.7

10.3 13.6 10.6 10.9 11.8 11.6 11.8 12.2

65.3 66.4 64.5 65.0 65.0 66.0 64.6 65.2

12.8 9.7 12.8 13.2 12.1 12.4 12.5 12.7

28.5 28.3 27.4 28.3 27.5 28.3 28.5 29.0

LSD (5%)

0.02

6.9

1.6

1.4

1.5

0.9

(g l' )

Mefluidide Mefluidide Mefluidide Mefluidide Mefluidide Mefluidide NAA

Significant effects 2':~ Rate DateL~

DateQ Rate × dateL Rate X dateQ

2.50 2.50 2.50 5.00 5.00 5.00 0.02

Date of application (days after full bloom) 0 7 15 0 7 15 7

L/D

ratio

NS ** ** ** NS

Flesh firmness

** NS ** NS **

NS NS ** NS *

NS NS NS NS *

NS NS ** NS *

NS NS NS NS *

'Means of the mefluidide treatments, NAA and the untreated control were separated by LSD. 2Linear and quadratic orthogonal contrasts were performed to test the trend of different rates and dates of application (date) ofmefluidide. 3NS, not significant, *, 5% level; **, 1% level; L, linear; Q, quadratic.

fruit as compared to that of the untreated control, N A A and mefluidide treatment at FB + 15 ( Table IV ). Flesh firmness was greater than that of untreated trees when mefluidide was applied at FB + 7 and FB + 15. Soluble solids exhibited a quadratic response to date of application and the interaction of rate and date of application. However, mefluidide at 2.5 g l-1 applied at FB was the only treatment that had lower soluble solids than the untreated control. All three components of fruit color (L,a,b) interacted significantly with the rate and date of application as a quadratic response. Mefluidide at 2.5 g 1-' applied to trees at FB + 7 produced fruit with less red color and which appeared less mature than those of the control. DISCUSSION

This study indicated that mefluidide treatments did not reduce fruit set, but resulted in poor return bloom. However, mefluidide applied at 5 g l - 1 at FB + 15 increased the fruit number at harvest as compared to the untreated controls.

19

The effect of mefluidide on fruit L/D ratios and soluble solids varied among cultivars. Generally, mefluidide treatments delayed maturity in that fruit color was altered, flesh firmness was increased and pre-harvest fruit drop was retarded. Although mefluidide did not effectively thin apples, this growth regulator may have a potential use as a "stop-drop" spray since fruit abscission was delayed. Mefluidide treatments applied prior to pre-harvest drop should be conducted to investigate this use. ACKNOWLEDGEMENT

The technical assistance of W.K.Patterson is gratefully acknowledged.

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