CHERIMOYA DORMANCY AND BASE TEMPERATURE DETERMINATION IN EXCISED 'FINO DE JETE' SHOOTS

Out-of-season cherimoya production depends on defoliation for removing floral buds from paradormancy exerted by subtending leaves. However, premature leaf removal does not succeed in stimulating early bloom since buds remain in rest until late winter. To determine the type of dormancy that cherimoya buds exhibit during autumn and winter, ‘Fino de Jete’ shoots, collected biweekly from October to April, were hand-defoliated, excised under water, uniformly cut to five nodes, and placed at 24°C in sucrose solution (7 g L^-1) in a growth chamber for 4 weeks. Only 5 and 35% of the treated shoots (1 and 14% of the buds) sprouted during early and mid-October, respectively. This percentage rapidly increased and stabilized in levels of 75% of shoots (40% of buds) in December. Evolution of bud break along the sampling period resembles the typical response of bud rest completion and suggests that cherimoya buds are truly endodormant during the first stages of autumn, being afterwards ecodormancy (the predominant factor inhibiting bud break before spring). Once the nature of bud dormancy was determined, we studied ‘Fino de Jete’ base temperature by cultivating ecodormant shoots at 11, 14, 17 or 24°C. Bud break was nil in shoots growing at 11 and 14°C. A percentage of 50% of shoots reached bud break after 4 weeks growing at 17°C (36% at bud level). This percentage reached 90% (72% of buds) at 24°C. The base temperature was, therefore, thought to be above 14°C, higher than previously reported, but in agreement with the phenology of the plant under natural conditions.