Relationship between the early development of apple fruiting branches and the regularity of bearing—An approach to the strategies of various cultivars

SummaryThe growth and fruiting pattern of fruiting branches of apple trees (Malus × domestica Borkh.) was investigated in several cultivars belonging to different ideotypes. The development of the laterals was described over several years, investigating the yearly changes in the bud type (latent, vegetative, non-bearing and bearing inflorescence, scar) since they first developed on one year old wood. The sequences were analysed by calculating the transition probabilities between the bud type of a given year and that of the following year, according to the age of the sequence. In general, the ability to produce a fruit bud after a fruit bud, i.e. the bourse-over-bourse phenomenon (β), and the ability to produce a fruit bud after a non-fruit bud (either vegetative or non-bearing inflorescence) (ϕ) tended to increase with time. The transition between latent buds and growing buds (vegetative or generative) was observed in all cultivars, but at a higher rate for ‘Fuji’, and did not vary according to the age of the sequence. The pattern of transition between growing buds and scar (extinction, i.e. physiological cessation of growth of the lateral) was different. First, 68% to 98% of all extinction phenomena appeared before the third year of the lateral. Second, cultivars such as Granny Smith and Red Winter, showed stronger extinction than spur-type cultivars. The balance between extinction and awakening of latent buds, called extinction assessment (ξ), was positively related to the bourse-over-bourse, over the first two couples of years of lateral life-span. The proportions of bud types on one year old wood was probably important in orientating the development of the laterals branched on the same parent shoot. Our results showed first that the first 2–3 years had a major effect on the development of the laterals over the following years, and secondly, that cultivar growth and fruiting pattern depended on a number of rather strictly defined rules (e.g. β, ϕ, ξ) the combinations of which determine the proper strategy of each cultivar. A better knowledge of these intrinsic rules should lead to an improvement in the training programme of young trees.