GENOTYPIC DIFFERENCES IN THE AXILLARY BUD GROWTH AND FRUITING PATTERNOF APPLE FRUITING BRANCHES OVER SEVERAL YEARS - AN APPROACH TO REGULATION OF FRUIT BEARING

Genotypic variations in growth and fruiting patterns were investigated in various apple (Malus X domestica Borkh.) cultivars belonging to di fferent ideotypes by analysis of chains of functions of laterals on fr uiting branches. Yearly changes in each axillary bud (latent, vegetati ve, non-bearing or bearing inflorescence and scar) were described over 5 or 6 years, depending on the cultivar. Sequences obtained for the v arious cultivars were analysed through calculations of three indices: fruit-richness( rho), alternation-to-fruit (alpha) and, among the alte rnating subsequences (i.e. bourse-shoot without a terminal fruit), alt ernation synchronism (sigma). The results showed that genotypes could be distinguished by two sets of characters. Some cultivars, such as 'R ed Winter', balance vegetative and reproductive growth by reducing the number of growing points through an extinction mechanism (essentially the abortion of potential bourse-shoots on non-bearing inflorescences ), and through a high functional autonomy (low alpha and high rho valu es) of the remaining sequences, corresponding to high bourse-over-bour se potentials. Spurred cultivars, such as 'Oregon Spur Delicious', wer e characterized by a low extinction value and, in a complementary way, did not seem able to fruit terminally on bourse-shoots (high alpha an d low rho values). The overall results of the study of sigma showed th at the alternation-to-fruit pattern (high alpha values) could be compl etely hidden when alternating sequences are desynchronized (low sigma values). The links between extinction and alternation-to-fruit, as wel l as the physiological significance of alternation synchronism, are di scussed.