CONSEQUENCES OF INSUFFICIENT WINTER CHILLING ON APPLE TREE BUD-BREAK

Abstract

Temperate fruit trees cultivated in regions of mild winter conditions, show several anomalies. Such anomalies are described, in a general way, as the budbreak absence and/or flowering delay. But after budbreak, fruit trees go on displaying anomalies like: paralysis of the shoot growth, development of small leaves, development of small flat shape fruits, low rate of effective fructification and reduction of the flowering-maturation cycle. Budbreak inductors do not influence the development of new leaves, and several times they stop the growth after budbreak. Among the problems of lack of chilling, the size and shape of the fruits, the low effective fructification and formation of small leaves in the shape of rosette are those that manifest more after artificial budbreak induction. INTRODUCTION A series of anomalies occurs when apple trees are cultivated in regions of mild winter, where the chilling requirements are not satisfying. Such anomalies, regarding to budbreak and flowering, have been described by several authors (Iuchi, 2002; Black, 1953; Bulon and Faust, 1995; Skinner, 1964; Saure, 1985; Chariani and Stebbins, 1994; Petri et al., 1996). But after budbreak and flowering, others anomalies go on persisting or manifesting during the cycle of the culture, and few studies describe and suggest measures that can minimize these problems. Nee and Fuchigami (1992) suggested two different approaches for overcoming rest: exit of the dormancy and elongation of the buds. The budbreak inductors can affect only the process of exit of the dormancy. However, the budbreak inductors do not influence the second approach, which involves the growth of the axillary buds and the development of the new leaves and fruits. The aim of this work is discuss and show the principle anomalies relating to the lack of chilling observed in the south of Brazil. MATERIAL AND METHODS The experiments were carried out in Cacador and Sao Joaquim, SC, Brazil. Cacador is located at 26°46’ S latitude, at 960 meters altitude, with 1067 chilling units (North Caroline modified model, Shaltout and Unrath, 1983). Sao Joaquim is located at 28°7’  S latitude, at 1353 meters altitude, with 2025 chilling units. The parameters analyzed were budbreak percentage, leaf area, average number of leaves by fructification organs and fruit size. They were sampled in five-years-old trees. The samples were collected in 10 randomized trees and for each tree 10 buds per type of bud (small spur, medium spur, big spur and brindle) were sampled. For statistical analysis Duncan test was used. RESULTS AND DISCUSSION Considering the great variability of the cold intensity in the different growing regions in the south of Brazil (Fig. 1), a series of anomalies, relating to the lack of chilling, are observed and present different intensities according to the region and year. Proc VII on TZFTS Eds. K.K. Jindal et al Acta Hort 662, ISHS 2004