INHERITANCE OF CHILLING REQUIREMENT FOR DORMANCY COMPLETION IN APRICOT VEGETATIVE BUDS

The pattern of vegetative bud dormancy was studied in apricot hybrid populations and the inheritance of chilling requirement evaluated. The study was carried out in Israel in a region with mild climate under natural conditions after two consecutive unusually warm winters. Vegetative bud breaking (BB) was estimated by evaluating 3 parameters: the level, the pattern, and the timing of BB on each of 1529 hybrids obtained from 44 crosses or open pollination. A most striking result was the high level of vegetative bud break registered especially during the first year of our two-year experiment, in progenies of all cultivars and selections including ones with high chilling requirements. On the other hand, a non-uniform pattern of vegetative development, reduced growth rate and a late bud breaking were characteristics found in both years in crosses with high chill parents. From the data obtained we concluded that the chilling requirement in apricot vegetative buds represents two distinct phenomena. The first is a genetically controlled switch of bud break, and the other phenomenon is the genetically control of vigor of the ensuing bud growth. The inheritance pattern of the first trait seems to be low chilling dominant while the second exhibits a non-dominant intermediate response between the parents. Both genes require exposure to chilling prior to activation but the first one responds to a lower level of chilling.

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