MEANS TO IMPROVE LEAFING OF PEACHES IN ISRAEL USING THE REST-AVOIDANCE TECHNIQUE

Under subtropical climates with mild winters and a relatively small difference in day length between summer and winter, entrance of fruit trees into a deep dormant state is more gradual than in the temperate zone and probably faster than in the tropics.
Using defoliation at the proper time induces a generally good bud break of floral buds but relatively poor break of vegetative buds.
By using rest-breaking chemicals we can improve considerably vegetative bud break but the growth obtained forms a rosette that is typified by the short internodes and by the formation of a resting terminal bud.
The result is a normal development of the flower and fruit but a shortage of photosynthesizing leaf area to support the developing fruits leading to production of small fruit, poor in sugar and quality.
The cause for the secondary domancy is a combination of the residual dormant state, the short days (down to 10.5 hrs) and the low temperatures in winter in Israel.
In tropical areas, the constant daylength of about 12 hrs and the relatively warm conditions are enough to prevent the rosette formation in peaches.
The shorter the daylength, the greater the risk of rosette formation.

In the present study an attempt was made to characterize the rosette formation and to improve the leaf area of trees forced to grow in autumn by chemical and physical means.
The effect of artificial chilling was compared with defoliation followed by rest-breaking chemicals with and without exposure to long days.
In addition, the effect of sprays with the growth regulators gibberellins and promalin on improving the vegetative growth was studied.
We found that only when exposed to chilling could the tree fully overcome the rosette formation.
Nevertheless, increase in day length as well as spray with both GA₃ and promalin increased the total leaf area produced.

Photosynthesis efficiency of autumn and spring leaves was studied as well as the relative importance of the three sources of carbohydrates for the fruits, namely: the reserves in the branches, autumn leaves and spring leaves.
It was shown that autumn leaves are of prime importance to the fruit developing in winter and that their photosynthesis capacity is not inferior to that of spring leaves.

III International Workshop on Temperate Zone Fruits in the Tropics and Subtropics

A. Erez, H. Lerner

https://doi.org/10.17660/ActaHortic.1990.279.27