APPLE OVULE SETTING

A study of the correlation between the number of the set ovules and fruit retention on trees until the physiological maturity phase was carried out on the following cultivars: ‘Royal Gala’, ‘Idared’, ‘Jonagold’, ‘Golden Delicious’ and ‘Granny Smith’, in an eight-year-old intensive orchard system on the rootstock M9 with trees spacing 4.0×1 m. Fruit yield in the orchard during the year of study was 21-24 kg/tree. Studied apple trees were not treated with fruit thinning agro-chemicals. The study of embryo development was conducted in three phases: 1) at the end of flowering; 2) during fruit shedding in June (on freshly shed fruits); and 3) at the moment of fruit physiological maturity before harvesting. Histo-cytological analysis showed normal constitution of female gametophyte and formation of pro-embryo without noticeable abortive process at the level of optical microscopy and histological sections 12 micrometers thick produced by parafine technique. Fruit analyses show that during the June fruit shedding were shed those fruits which on average had less than 30% of ovules with normally developed embryos. Furthermore, among the same cultivars observed, physiologically mature fruits set for harvesting on average had over 70% of normally developed embryos, with that in diploid cultivars it was over 75%, and in the triploid cultivar ‘Jonagold’ the number was above 55%. Genotype differences in the structure of the developed embryos in both shed and physiologically mature fruits were discussed in this paper as the limiting factor of apple tree yield capacity in intensive orchard management systems.