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Ethylene influence on leaf and fruit detachment in ‘Manzanillo’ olive trees
Scientia Horticulturae, 4(1976)337--344
337
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
ETHYLENE INFLUENCE ON LEAF AND FRUIT DETACHMENT IN 'MANZANILLO' OLIVE TREES
Y. BEN-TAL and S. LAVEE
Institute of Horticulture, Agricultural Research Organization, The Volcani Center, Bet-Dagan (Israel) No. l 1 2 / E , 1975 Series. (First received 29 July 1975; in revised form 6 November 1975 )
ABSTRACT Ben--Tal, Y. and Lavee, S., 1976. Ethylene influence on leaf and fruit detachment in 'Manzanillo' olive trees. Scientia Hort., 4: 337--344. The fruit removal force ( F R F ) of olive fruits decreased after treatment with the ethylene-releasing agents CGA 13'586 and ethephon. The former has a higher pH in solution and releases ethylene quickly and in very large amounts, while the latter has a much lower pH and releases ethylene slowly and in much smaller concentrations. The influence of each of the agents on the F R F followed a parallel pattern to its ethylene evolution; CGA 13'586 caused a fast and continuous decrease in the F R F , while ethephon caused a small reduction, a period of steady state and a second reduction in the FRF. At the end of the second stage the F R F was similar for both chemicals. A possible mode of action for the two chemicals is suggested.
INTRODUCTION
The problem of mechanical harvesting of olives has not been solved yet, but has interested many workers. Most of them tried to affect the development of an abscission layer in the pedicel, therefore decreasing the pull-force or fruit removal force (FRF) required for hand or mechanical harvesting (Charier, 1970; CoUina and Zucconi, 1966; Fridley et al., 1971; Hartmann et al., 1967; Jacoboni and Battaglini, 1970; Lavee et al., 1970, 1973). The chemicals used were ethylene-releasing agents (Hartmann et al., 1970; Lavee and Haskal, 1975), halogenated acetates (Collina and Zucconi, 1966; Hartmann et al., 1967; Lavee et al., 1973), or natural and artificial auxins (Cellini et al., 1966; Hartmann et al., 1967, 1970). Some workers have shown the relationship between ethylene-releasing or inducing chemicals and fruit abscission in peach (Buchanan and Biggs, 1969}, cherry and plum (Bukovac et al., 1969; Wittenbach and Bukovac, 1974), apple and peach (Edgerton and Greenhalgh, 1969), pear (Griggs et al., 1970), cucumber (Jackson et al., 1972) and cotton (Lipe and Morgan, 1973).
338
Lavee et al. (1973) and Lavee and Haskal (1975) have shown that the F R F required for olive fruit detachment after ethephon treatment was reduced considerably 7 days after the application of the chemical. They also arrived at an optimal concentration of ethephon and CGA 13'586 which reduces the F R F value without causing severe leaf shed. In this study we tested the effect of ethylene-releasing and -inducing chemicals during the first 96 h after application by measuring the concentration of ethylene in leaves and fruits during this period. MATERIALS AND METHODS Mature irrigated olive trees (cultivar 'Manzanillo') were selected for the experiments. Similar trees were sprayed with a high pressure mechanical sprayer using 15--25 1 per tree. The solutions included 0.025% Triton x-100 as a wetting-agent unless otherwise specified. The control trees were sprayed with a similar volume of water with the wetting-agent. Whenever detached leaves were tested, they were dipped in the proper solutions and air-dried before further treatments. Samples were collected immediately after spraying, every 4 h during the first 12 h, and every 12 h afterwards. Chemicals. - - The chemicals tested were ethephon (2-chloro-ethanephosphonic acid, supplied complimentarily by the Agan Corp., Israel) at 1250 p.p.m.; and CGA 13'586, a p r o d u c t of Ciba-Geigy (2-chloroethyltris-(-2 methoxyethoxy)-silane, supplied complimentarily by C.T.S. Ltd., Israel) at 3000 p.p.m. Lavee and Haskal (unpublished data) found these concentrations to be optimal for both hand and mechanical harvestihg. They represent similar molar concentrations: 8.3 X 10 -s M for ethephon and 9.4 X 10 -3 M for CGA. Ethylene measurements. - - Fruits and leaves were picked from the trees at different times after the application of the chemicals. Half of the leaves and the fruits of every treatment were thoroughly washed under running tap water. Four 100-g samples of washed fruits and 4 samples of unwashed fruits were sealed separately in 250 ml Erlenmeyer flasks for 30 min at 24 °C. Four 2-g samples of washed and of unwashed fresh leaves were sealed in 30-ml vials for 30 min at 24 °C. Two grams of fresh leaves contained 10--12 leaves. Therefore, 11 leaves which had died naturally and which weighed c. 0.75 g, were used as the dead-leaves control. T w o ml of air was taken with a syringe from each flask or tube and injected into a gas chromatograph for determination of the ethylene concentration. The ethylene concentration was determined by means of a Packard gas chromatograph using an alumina column and a flame ionization detector. The build-up of CO2 was linear during the first hour in the sealed containers and reached a concentration of a b o u t 1.25% at the end of the first 30 min (Fig.l). The CO2 was determined in separate parallel samples of fruits with a Porapak type R column and a thermal conductivity detector.
339
2512.Ok i
!
v 1,5 z @ w c9 ~1.0
0.5
0
]
] 20
I 40 TIME (min)
I
I 60
Fig. 1. Carbon dioxide accumulation in the atmosphere of sealed olive fruits. Three olive fruits were sealed in 30-ml vials. Samples were taken every 10 min and tested for CO2 concentrations in a gas chromatograph as described in the text. measurements. - - Every time fruits were picked from f~e trees at least 10 fruits were detached with the aid of a Chatillon d y n a m o m e t e r which indicated the F R F required for the d e t a c h m e n t of the fruits. The results are statistical means of the F R F values at each harvest. FRF
RESULTS The evolution of ethylene from the samples picked at different times after the application of the chemicals is shown in Figs. 2 and 3. The release of ethylene right after the treatment was very large and diminished with time. However, while the ethylene f o r m e d from the CGA 13'586 continued to decrease, the ethylene concentration formed from the ethephon started to increase during the third day after treatment. This p h e n o m e n o n appeared in leaves and fruits whether t h e y were rinsed or not, but did n o t appear when dead leaves were treated with ethephon, as can be seen in Fig. 4. Measurements of the F R F , which indicate the force in grams necessary to pick fruit from the tree (Table 1) showed that values started to decrease 24 h after treatment. On the trees treated with CGA 13'586 the reduction in F R F was continuous and after 4 days was about 25 % of the control. The
340
1.2,
2.0 l 0.9
REGULARIWASHED ~. ~~ ID,~ CGA 13'586 i -" O-----(3 ETHEPHON ~ O- -- < ) CONTROL
REGULAR WASHED I _.~ ± E,--- .-,& CGA13'586 | --'= {3- - ~ ETHEPHON~ ?. --." O-- .-(3 CONTROL
0.9
/
t
"E 0.6
(3_ v
i
03i
4
o
8
0.09
0.05
0
12
24
36
48
60
TIME (hr)
72
84
96
12
24
36
48
60
TIME (hr)
o
~
72
84
96
Fig. 2. The effect of ethephon and C G A 13'586 on the concentration of ethylene formed in olive fruits.One hundred g of olive fruits were sealed in 250-mi Erlenmeyer flasks for 30 min. A 2-ml sample was taken from each flask for an ethylene test. The results are means of 4 replicates. Values are given in p.p.m./100g/min. Fig. 3. The effect of ethephon and C G A 13'586 on the concentration of ethylene formed in olive leaves. T w o g of olive leaves were sealed in 30-ml vials for 30 min. A 2-ml sample was taken from each vial for an ethylene test. The results are means of 4 replicates.'Values are given in p.p.m./2g/min.
reduction in FRF on the ethephon-treated trees was reduced after 24 h; then it stayed constant for 48 h, which was also the period when the ethylene concentration remained constant. The FRF started to decrease after 96 h following the renewed increase in ethylene evolution (Figs. 2 and 3). It should be noted, however, that in order to achieve a similar FRF with the 2 chemicals, 7--8 days were needed with ethephon while only 4 days Were needed with CGA 13'586. But, the effect of ethephon on the leaves was even stronger as it caused a considerably greater leaf drop than the CGA 13'586. Measurements of the pH of the chemical solutions used indicated that the pH of CGA 13'586 was higher than that of the ethephon solution, and that the former released much more ethylene than the latter (Table 3). DISCUSSION
It has been shown by Abeles et al. (1971), Jackson and Osborne (1972), Henry et al. (1973, 1974) and many others, that ethylene induces, and may advance, the initiation of an abscission layer in the pedicels of leaves, flowers
341
20.0~
REGULARWASHED
~- \
A----~h~---a CC~ 13'586-
•^ ^ ~ \ tu'uz~-y. ~
H
[3- - G ETHEPHON_ O- - <) CONTROL_
i \
-.eL
0
24
- -:L- - -"c~ ---B
48 TIME (6r)
72
96
Fig. 4. T h e e f f e c t o f e t h e p h o n a n d C G A 1 3 ' 5 8 6 o n t h e c o n c e n t r a t i o n o f e t h y l e n e f o r m e d in d e a d olive leaves. E l e v e n n a t u r a l l y - d e a d leaves w e i g h i n g 0 . 7 3 - - 0.78 g were sealed in 30-ml vials for 30 rain. A 2-ml s a m p l e was t a k e n f r o m e a c h vial f o r an e t h y l e n e test. T h e results are m e a n s o f 4 replicates. Values are given in p . p . m . / 0 . 7 5 g / m i n . TABLE 1 T h e e f f e c t o f e t h e p h o n a n d C G A 1 3 ' 5 8 6 o n t h e f r u i t r e m o v a l force ( F R F ) o f ' M a n z a n i l l o ' olive fruits. A t least 10 fruits were p i c k e d w i t h t h e aid o f a C h a t i l l o n d y n a m o m e t e r for each replicate. T h e results are m e a n s of 4 replicates. Values are given in grams. Treatment
Con~ol Ethephon CGA 13'586
Hoursa~ertreatment 0
24
48
72
96
560 550 542
490 416 444
552 418 297
561 427 242
523 346 116
and fruits. Therefore, it was assumed that the two chemicals, by releasing ethylene, induced or advanced the formation of an abscission layer in the olive fruit pedicels. It seems that both chemicals are readily absorbed, as within 4 h from the time of application the differences in ethylene evolution between washed and unwashed leaves or fruits were minute. Lavee and Haskal (unpublished data) found that the two chemicals were
342 TABLE 2 The effect of ethephon and CGA 13'586 on the fruit removal force (FRF) of 'Suri' and 'Nabali' olive fruits. Four 'Suri' or 'Nabali' olive trees were sprayed for every treatment. The results are means of at least 400 fruits/treatment picked with the aid of the dynamometer. Treatment Control Ethephon CGA 13'586
After 3 days
'Suri' After 8 days
'Nabali' After 7 days
420 255 55
412 115 54
405 28 29
TABLE 3 The pH of aqueous solutions of ethephon and CGA 13'586 used, and their natural ethylene release. Solutions made with tap wa~r, 1 ml solution sealed in a 30 ml vial for 30 rain. Samples of 2 ml atmosphere were taken for injection. Treatment
pH
p.p.m./ml/min
0.025 % Triton x-100 1250 p.p.m, ethephon + 0.025 % Triton x-100
7.47 2.85
0.002 0.086
3000 p.p.m. CGA 13'586
7.12
69.407
similarly e f f e c t i v e in r e d u c i n g t h e F R F o f olive fruits. B u t , while o p t i m a l conc e n t r a t i o n f o r e t h e p h o n was 1 2 5 0 p . p . m , a n d its l o w e s t F R F value was reached only 7 days after application, the CGA 13'586 optimal concentrat i o n was 3 0 0 0 p . p . m , a n d its l o w e s t F R F value was r e a c h e d 3 d a y s a f t e r application. As b o t h c h e m i c a l s are basically s i m i l a r - - ( e t h y l e n e - r e l e a s i n g c o m p o u n d s ) it was i n t e r e s t i n g a n d i m p o r t a n t t o find h o w t h e i r c h e m i c a l differences result in such a significant p h y s i o l o g i c a l d i f f e r e n c e . T h e d i f f e r e n c e s b e t w e e n the e t h y l e n e e v o l u t i o n f r o m t h e t w o c h e m i c a l s i n d i c a t e t h a t C G A 1 3 ' 5 8 6 releases large q u a n t i t i e s o f e t h y l e n e . This e x o g e n o u s e t h y l e n e p r o b a b l y e n h a n c e s t h e m a t u r a t i o n o f t h e abscission layer, t h u s r e d u c i n g t h e F R F . E t h e p h o n , o n t h e o t h e r h a n d , is a t w o - p u r p o s e c o m p o u n d . D u r i n g t h e first 72 h it releases an a m o u n t o f e t h y l e n e w h i c h a f f e c t s t h e F R F t o a c e r t a i n degree b y t h e s a m e m e c h a n i s m as d o e s t h e C G A 1 3 ' 5 8 6 . H o w e v e r , a f t e r t h e first 72 h it s e e m s t o i n d u c e t h e p r o d u c t i o n o f e n d o g e n o u s e t h y l e n e w h i c h in t u r n is f o l l o w e d b y a n o t h e r decrease in t h e F R F . T h e late increase in e t h y l e n e s e c r e t i o n c o u l d n o t be a d e l a y e d release o f e t h y l e n e f r o m t h e original e x o g e n o u s e t h e p h o n b e c a u s e it did n o t o c c u r w i t h t r e a t e d d e a d leaves.
343
The F R F values measured after CGA 13'586 treatment seemed to be due mostly to a direct ethylene release from this compound, and were therefore reached much faster (within 3--4 days). The F R F values measured after ethephon treatment are suggested to be a combined result of the ethylene released from the ethephon, and the endogenous ethylene induced at a later stage. It also explains why 7 days are needed to reach a similar level of FRF values after ethephon treatment. Objection could be made to the fact that the pH of the 2 solutions was different. This was done for practical reasons, because growers use the substances with different (their "own") pH. However, we stress that similar effects of the 2 compounds are obtained regarding the rate of ethylene evolution, the time necessary to reach least removal force and the defoliation, if the pH of the solutions is the same. This point will be clarified in a following publication.
REFERENCES
Abeles, F.B., Craker, L.E. and Leather, G.R., 1971. Abscission: the phytogerontological effects of ethylene. Plant Physiol., 47: 7--9. Buchanan, D.W. and Biggs, R.H., 1969. Peach fruit abscission and pollen germination as influenced by ethylene and 2-chloroethanephosphonic acid. J. Amer. Soc. Hort. Sci., 94: 327--329. Bukovac, M.J., Zucconi, F., Larsen, R.P. and Kesner, C.D., 1969. Chemical promotion of fruit abscission in cherries and plums with special reference to 2-chlor0ethanephosphonic acid. J. Amer. Soc. Hort. Sci., 94: 226--230. Charlet, L.F., 1970. Probl~mes pos~s par la cueillette des olives en France. Premiers essais de m~canisation de la r~colte. Inform. Oleic. Int., 50/51 : 21--36. Collina, F. and Zucconi, F., 1966. Ricerche sull'impiego di prodetti chimici atti a facilitate la raccolta delle olive. III. Ricerca comparativa sulla efficacia di prodotti diversi. Atti Reale Accad. Georgofili 142, Suppl. Vol. XIII. Edgerton, L.T. and Greenhalgh, W.S., 1969. Regulation of growth, flowering and fruit abscission with 2-chloroethanephosphonic acid. J. Amer. Soc. Hort. Sci., 94: 11--13. Fridley, R.B., Hartmann, H.T., Mehlschau, J.J., Chen, B. and Whisler, J., 1971. Olive harvest mechanization in California. Bull. Univ. Calif. Agr. Exp. Stn. 855. Cellini, R., Falusi, M. and Sabato, S., 1966. Ricerche sull'attitudine dell' acido 2,4,5 tri-chlorofenossipropionico ad attenuare la cascola tardiva delle olive. Atti Reale Accad. Georgofili., 142: 95--100. Griggs, W.H., Iwakiri, B.T., Fridley, R.B. and Mehlaschau, J., 1970. Effect of 2-chloroethylphosphonic acid and cycloheximide on abscission and ripening of Bartlett pears. HortScience, 5: 264--266. Hartmann, H.T., Fadl, M. and Whisler, J., 1967. Inducing abscission of olive fruits by spraying with ascorbic acid and indoleacetic acid. Calif. Agr., 21 (7): 5--7. Hartmann, H.T., Tornbesi, A. and Whisler, J., 1970. Promotion of ethylene evolution and fruit abscission in the olive by 2-chloroethanephosphonic acid and cycloheximide. J. Amer. Soc. Hort. Sci., 95: 535--540. Henry, E.W. and Jensen, T.E., 1973. Peroxidases in tobacco abscission zone tissue. L Fine structural localization in cell walls during ethylene induced abscission. J. Cell Sci., 13: 591~601. Henry, E.W., Valdovinos, J.G. and Jensen, J.E., 1974. Peroxidases in tobacco abscission zone tissue. II. Time course studies of peroxidase activity during ethylene induced abscission. Plant Physiol., 54: 192--196.
344 Jackson, M.B. and Osborne, D.J., 1972. Abscisic acid, auxin and ethylene in explants abscission. J. Exp. Bot., 23: 849--862. Jackson, M.B., Morrow, I.B. and Osborne, D.J., 1972. Abscission and dehiscence in the squirting cucumber EcbaUium elaterium. Regulation by ethylene. Can. J. Bot., 50: 1465--1471. Jacoboni, N. and Battaglini, M., 1970. Nouveaux r~sultats et perspectives des ~tudes conduites en Italie sur la r~colte m~canique des olives. Information Oleic. Int., 50/51 : 59--89. Lavee, S. and Haskal, A., 1975. Studies with ethephon for facilitating olive harvest. Scientia Hort., 3 : 163--171. Lavee, S., Sarig, Y. and Haskal, A., 1970. Les traitements chimiques facilitant le d~veloppement du fruit et l'abscission, et leur relation avec la r~colte m~canique des olives. Inform. Oleic. Int., 50/51: 37--57. I~vee, S., Barshi, G. and Haskal, A., 1973. Natural fruit drop and induced abscission to facilitate mechanical harvesting of 'Manzanillo' and 'Suri' olives. Scientia Hort., 1: 63--75. Lipe, J.A. and Morgan, P.W., 1973. Ethylene, a regulator of young fruit abscission. Plant Physiol., 51: 949--953. Wittenbach, V.A. and Bukovac, M.J., 1974. Cherry fruit abscission. Evidence for time of initiation and the involvement of ethylene. Plant Physiol., 54: 494--498.
337
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
ETHYLENE INFLUENCE ON LEAF AND FRUIT DETACHMENT IN 'MANZANILLO' OLIVE TREES
Y. BEN-TAL and S. LAVEE
Institute of Horticulture, Agricultural Research Organization, The Volcani Center, Bet-Dagan (Israel) No. l 1 2 / E , 1975 Series. (First received 29 July 1975; in revised form 6 November 1975 )
ABSTRACT Ben--Tal, Y. and Lavee, S., 1976. Ethylene influence on leaf and fruit detachment in 'Manzanillo' olive trees. Scientia Hort., 4: 337--344. The fruit removal force ( F R F ) of olive fruits decreased after treatment with the ethylene-releasing agents CGA 13'586 and ethephon. The former has a higher pH in solution and releases ethylene quickly and in very large amounts, while the latter has a much lower pH and releases ethylene slowly and in much smaller concentrations. The influence of each of the agents on the F R F followed a parallel pattern to its ethylene evolution; CGA 13'586 caused a fast and continuous decrease in the F R F , while ethephon caused a small reduction, a period of steady state and a second reduction in the FRF. At the end of the second stage the F R F was similar for both chemicals. A possible mode of action for the two chemicals is suggested.
INTRODUCTION
The problem of mechanical harvesting of olives has not been solved yet, but has interested many workers. Most of them tried to affect the development of an abscission layer in the pedicel, therefore decreasing the pull-force or fruit removal force (FRF) required for hand or mechanical harvesting (Charier, 1970; CoUina and Zucconi, 1966; Fridley et al., 1971; Hartmann et al., 1967; Jacoboni and Battaglini, 1970; Lavee et al., 1970, 1973). The chemicals used were ethylene-releasing agents (Hartmann et al., 1970; Lavee and Haskal, 1975), halogenated acetates (Collina and Zucconi, 1966; Hartmann et al., 1967; Lavee et al., 1973), or natural and artificial auxins (Cellini et al., 1966; Hartmann et al., 1967, 1970). Some workers have shown the relationship between ethylene-releasing or inducing chemicals and fruit abscission in peach (Buchanan and Biggs, 1969}, cherry and plum (Bukovac et al., 1969; Wittenbach and Bukovac, 1974), apple and peach (Edgerton and Greenhalgh, 1969), pear (Griggs et al., 1970), cucumber (Jackson et al., 1972) and cotton (Lipe and Morgan, 1973).
338
Lavee et al. (1973) and Lavee and Haskal (1975) have shown that the F R F required for olive fruit detachment after ethephon treatment was reduced considerably 7 days after the application of the chemical. They also arrived at an optimal concentration of ethephon and CGA 13'586 which reduces the F R F value without causing severe leaf shed. In this study we tested the effect of ethylene-releasing and -inducing chemicals during the first 96 h after application by measuring the concentration of ethylene in leaves and fruits during this period. MATERIALS AND METHODS Mature irrigated olive trees (cultivar 'Manzanillo') were selected for the experiments. Similar trees were sprayed with a high pressure mechanical sprayer using 15--25 1 per tree. The solutions included 0.025% Triton x-100 as a wetting-agent unless otherwise specified. The control trees were sprayed with a similar volume of water with the wetting-agent. Whenever detached leaves were tested, they were dipped in the proper solutions and air-dried before further treatments. Samples were collected immediately after spraying, every 4 h during the first 12 h, and every 12 h afterwards. Chemicals. - - The chemicals tested were ethephon (2-chloro-ethanephosphonic acid, supplied complimentarily by the Agan Corp., Israel) at 1250 p.p.m.; and CGA 13'586, a p r o d u c t of Ciba-Geigy (2-chloroethyltris-(-2 methoxyethoxy)-silane, supplied complimentarily by C.T.S. Ltd., Israel) at 3000 p.p.m. Lavee and Haskal (unpublished data) found these concentrations to be optimal for both hand and mechanical harvestihg. They represent similar molar concentrations: 8.3 X 10 -s M for ethephon and 9.4 X 10 -3 M for CGA. Ethylene measurements. - - Fruits and leaves were picked from the trees at different times after the application of the chemicals. Half of the leaves and the fruits of every treatment were thoroughly washed under running tap water. Four 100-g samples of washed fruits and 4 samples of unwashed fruits were sealed separately in 250 ml Erlenmeyer flasks for 30 min at 24 °C. Four 2-g samples of washed and of unwashed fresh leaves were sealed in 30-ml vials for 30 min at 24 °C. Two grams of fresh leaves contained 10--12 leaves. Therefore, 11 leaves which had died naturally and which weighed c. 0.75 g, were used as the dead-leaves control. T w o ml of air was taken with a syringe from each flask or tube and injected into a gas chromatograph for determination of the ethylene concentration. The ethylene concentration was determined by means of a Packard gas chromatograph using an alumina column and a flame ionization detector. The build-up of CO2 was linear during the first hour in the sealed containers and reached a concentration of a b o u t 1.25% at the end of the first 30 min (Fig.l). The CO2 was determined in separate parallel samples of fruits with a Porapak type R column and a thermal conductivity detector.
339
2512.Ok i
!
v 1,5 z @ w c9 ~1.0
0.5
0
]
] 20
I 40 TIME (min)
I
I 60
Fig. 1. Carbon dioxide accumulation in the atmosphere of sealed olive fruits. Three olive fruits were sealed in 30-ml vials. Samples were taken every 10 min and tested for CO2 concentrations in a gas chromatograph as described in the text. measurements. - - Every time fruits were picked from f~e trees at least 10 fruits were detached with the aid of a Chatillon d y n a m o m e t e r which indicated the F R F required for the d e t a c h m e n t of the fruits. The results are statistical means of the F R F values at each harvest. FRF
RESULTS The evolution of ethylene from the samples picked at different times after the application of the chemicals is shown in Figs. 2 and 3. The release of ethylene right after the treatment was very large and diminished with time. However, while the ethylene f o r m e d from the CGA 13'586 continued to decrease, the ethylene concentration formed from the ethephon started to increase during the third day after treatment. This p h e n o m e n o n appeared in leaves and fruits whether t h e y were rinsed or not, but did n o t appear when dead leaves were treated with ethephon, as can be seen in Fig. 4. Measurements of the F R F , which indicate the force in grams necessary to pick fruit from the tree (Table 1) showed that values started to decrease 24 h after treatment. On the trees treated with CGA 13'586 the reduction in F R F was continuous and after 4 days was about 25 % of the control. The
340
1.2,
2.0 l 0.9
REGULARIWASHED ~. ~~ ID,~ CGA 13'586 i -" O-----(3 ETHEPHON ~ O- -- < ) CONTROL
REGULAR WASHED I _.~ ± E,--- .-,& CGA13'586 | --'= {3- - ~ ETHEPHON~ ?. --." O-- .-(3 CONTROL
0.9
/
t
"E 0.6
(3_ v
i
03i
4
o
8
0.09
0.05
0
12
24
36
48
60
TIME (hr)
72
84
96
12
24
36
48
60
TIME (hr)
o
~
72
84
96
Fig. 2. The effect of ethephon and C G A 13'586 on the concentration of ethylene formed in olive fruits.One hundred g of olive fruits were sealed in 250-mi Erlenmeyer flasks for 30 min. A 2-ml sample was taken from each flask for an ethylene test. The results are means of 4 replicates. Values are given in p.p.m./100g/min. Fig. 3. The effect of ethephon and C G A 13'586 on the concentration of ethylene formed in olive leaves. T w o g of olive leaves were sealed in 30-ml vials for 30 min. A 2-ml sample was taken from each vial for an ethylene test. The results are means of 4 replicates.'Values are given in p.p.m./2g/min.
reduction in FRF on the ethephon-treated trees was reduced after 24 h; then it stayed constant for 48 h, which was also the period when the ethylene concentration remained constant. The FRF started to decrease after 96 h following the renewed increase in ethylene evolution (Figs. 2 and 3). It should be noted, however, that in order to achieve a similar FRF with the 2 chemicals, 7--8 days were needed with ethephon while only 4 days Were needed with CGA 13'586. But, the effect of ethephon on the leaves was even stronger as it caused a considerably greater leaf drop than the CGA 13'586. Measurements of the pH of the chemical solutions used indicated that the pH of CGA 13'586 was higher than that of the ethephon solution, and that the former released much more ethylene than the latter (Table 3). DISCUSSION
It has been shown by Abeles et al. (1971), Jackson and Osborne (1972), Henry et al. (1973, 1974) and many others, that ethylene induces, and may advance, the initiation of an abscission layer in the pedicels of leaves, flowers
341
20.0~
REGULARWASHED
~- \
A----~h~---a CC~ 13'586-
•^ ^ ~ \ tu'uz~-y. ~
H
[3- - G ETHEPHON_ O- - <) CONTROL_
i \
-.eL
0
24
- -:L- - -"c~ ---B
48 TIME (6r)
72
96
Fig. 4. T h e e f f e c t o f e t h e p h o n a n d C G A 1 3 ' 5 8 6 o n t h e c o n c e n t r a t i o n o f e t h y l e n e f o r m e d in d e a d olive leaves. E l e v e n n a t u r a l l y - d e a d leaves w e i g h i n g 0 . 7 3 - - 0.78 g were sealed in 30-ml vials for 30 rain. A 2-ml s a m p l e was t a k e n f r o m e a c h vial f o r an e t h y l e n e test. T h e results are m e a n s o f 4 replicates. Values are given in p . p . m . / 0 . 7 5 g / m i n . TABLE 1 T h e e f f e c t o f e t h e p h o n a n d C G A 1 3 ' 5 8 6 o n t h e f r u i t r e m o v a l force ( F R F ) o f ' M a n z a n i l l o ' olive fruits. A t least 10 fruits were p i c k e d w i t h t h e aid o f a C h a t i l l o n d y n a m o m e t e r for each replicate. T h e results are m e a n s of 4 replicates. Values are given in grams. Treatment
Con~ol Ethephon CGA 13'586
Hoursa~ertreatment 0
24
48
72
96
560 550 542
490 416 444
552 418 297
561 427 242
523 346 116
and fruits. Therefore, it was assumed that the two chemicals, by releasing ethylene, induced or advanced the formation of an abscission layer in the olive fruit pedicels. It seems that both chemicals are readily absorbed, as within 4 h from the time of application the differences in ethylene evolution between washed and unwashed leaves or fruits were minute. Lavee and Haskal (unpublished data) found that the two chemicals were
342 TABLE 2 The effect of ethephon and CGA 13'586 on the fruit removal force (FRF) of 'Suri' and 'Nabali' olive fruits. Four 'Suri' or 'Nabali' olive trees were sprayed for every treatment. The results are means of at least 400 fruits/treatment picked with the aid of the dynamometer. Treatment Control Ethephon CGA 13'586
After 3 days
'Suri' After 8 days
'Nabali' After 7 days
420 255 55
412 115 54
405 28 29
TABLE 3 The pH of aqueous solutions of ethephon and CGA 13'586 used, and their natural ethylene release. Solutions made with tap wa~r, 1 ml solution sealed in a 30 ml vial for 30 rain. Samples of 2 ml atmosphere were taken for injection. Treatment
pH
p.p.m./ml/min
0.025 % Triton x-100 1250 p.p.m, ethephon + 0.025 % Triton x-100
7.47 2.85
0.002 0.086
3000 p.p.m. CGA 13'586
7.12
69.407
similarly e f f e c t i v e in r e d u c i n g t h e F R F o f olive fruits. B u t , while o p t i m a l conc e n t r a t i o n f o r e t h e p h o n was 1 2 5 0 p . p . m , a n d its l o w e s t F R F value was reached only 7 days after application, the CGA 13'586 optimal concentrat i o n was 3 0 0 0 p . p . m , a n d its l o w e s t F R F value was r e a c h e d 3 d a y s a f t e r application. As b o t h c h e m i c a l s are basically s i m i l a r - - ( e t h y l e n e - r e l e a s i n g c o m p o u n d s ) it was i n t e r e s t i n g a n d i m p o r t a n t t o find h o w t h e i r c h e m i c a l differences result in such a significant p h y s i o l o g i c a l d i f f e r e n c e . T h e d i f f e r e n c e s b e t w e e n the e t h y l e n e e v o l u t i o n f r o m t h e t w o c h e m i c a l s i n d i c a t e t h a t C G A 1 3 ' 5 8 6 releases large q u a n t i t i e s o f e t h y l e n e . This e x o g e n o u s e t h y l e n e p r o b a b l y e n h a n c e s t h e m a t u r a t i o n o f t h e abscission layer, t h u s r e d u c i n g t h e F R F . E t h e p h o n , o n t h e o t h e r h a n d , is a t w o - p u r p o s e c o m p o u n d . D u r i n g t h e first 72 h it releases an a m o u n t o f e t h y l e n e w h i c h a f f e c t s t h e F R F t o a c e r t a i n degree b y t h e s a m e m e c h a n i s m as d o e s t h e C G A 1 3 ' 5 8 6 . H o w e v e r , a f t e r t h e first 72 h it s e e m s t o i n d u c e t h e p r o d u c t i o n o f e n d o g e n o u s e t h y l e n e w h i c h in t u r n is f o l l o w e d b y a n o t h e r decrease in t h e F R F . T h e late increase in e t h y l e n e s e c r e t i o n c o u l d n o t be a d e l a y e d release o f e t h y l e n e f r o m t h e original e x o g e n o u s e t h e p h o n b e c a u s e it did n o t o c c u r w i t h t r e a t e d d e a d leaves.
343
The F R F values measured after CGA 13'586 treatment seemed to be due mostly to a direct ethylene release from this compound, and were therefore reached much faster (within 3--4 days). The F R F values measured after ethephon treatment are suggested to be a combined result of the ethylene released from the ethephon, and the endogenous ethylene induced at a later stage. It also explains why 7 days are needed to reach a similar level of FRF values after ethephon treatment. Objection could be made to the fact that the pH of the 2 solutions was different. This was done for practical reasons, because growers use the substances with different (their "own") pH. However, we stress that similar effects of the 2 compounds are obtained regarding the rate of ethylene evolution, the time necessary to reach least removal force and the defoliation, if the pH of the solutions is the same. This point will be clarified in a following publication.
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