Quantification of bearing habit on the basis of lateral bud growth of seven pear cultivars grown under conditions of inadequate winter chilling in South Africa
The bearing habit of seven pear cultivars was quantified according to the ontogenetic development from axillary buds, i.e. developmental changes in the terminal position of laterals on fruiting branches. Ten non-pruned branches of seven pear cultivars, i.e. Forelle (on Quince A and BP1 rootstocks), Abaté Fetel, Flamingo, Packham's Triumph, Golden Russet Bosc, Rosemarie and Beurre D'Anjou (all on BP1 rootstock) were observed. Description started with the development of the main fruiting branch, forming several leaves in the first year of growth (designated year Y), with meristems developing in the leaf axils. In the following season (year Y + 1), these buds had five developmental alternatives: to remain as a latent bud (L), to develop as a vegetative bud (V), to become a flower bud without fruit (F), to become a flower bud setting a fruit (P), or to abort and leave a scar (S). Each year the development of these buds was observed and classified anew, giving rise to sequences describing up to 5 years of development. From 44% ('Beurre D'Anjou') to 79% ('Flamingo') of laterals remained in the growing phase (phase G comprising of V, F or P buds). This coincided with low proportions of buds remaining in the latent phase (L), with even fewer buds moving to the ending state (S; extinction mechanism). A relatively large proportion of growing laterals went from the growing phase back to the latent phase (up to 21% in the case of 'Beurre D'Anjou'), probably due to inadequate winter chilling. The predominant bud type in the growing stage was vegetative (V). Although flowering was generally low, 'Flamingo' and 'Abaté Fetel' became reproductive (F or P) in year Y + 3. 'Packham's Triumph' and 'Rosemarie' displayed F and P buds in year Y + 1, corresponding to the ability of these cultivars to bear fruit on longer 1-year-old shoots. Although the occurrence of the extinction mechanism was low, the higher proportion of latent buds may aid in reducing the number of growing buds, thereby increasing the allocation of assimilates to fruiting structures. This, in combination with the tendency of 'Packham's Triumph' and 'Rosemarie' to develop longer, more autonomous shoots, may explain their higher productivity and the occurrence of bourse-over-bourse bearing. © 2002 Elsevier Science B.V. All rights reserved.