Dormência da macieira no Sul do Brasil: aspectos fisiológicos e modelos estimadores de necessidades térmicas

Abstract

Apple trees come from regions with a typically temperate climate and, when they are cultivated in Brazil, they usually present adaptive problems, resulting in lower productions. To correct these problems, budburst inducers are used, especially hydrogenated cyanamide (Dormex®), which is a product that presents toxicity. In this sense, alternatives of budburst inducers should be studied, as well as antioxidant enzymes, because the action of budburst inducers depends on these. Apple trees require chilling during endodormancy and heat after this phase to evaluate these requirements and to offer chilling and heat, when estimating models of cold accumulation and thermal sum were used. The objective of this thesis was to understand the antioxidant enzymes activity in response to the application of budburst inducers, to seek new alternatives to budburst inducers, and to evaluate the efficiency of estimating models of cold accumulation and thermal sum. The antioxidant enzymes activity in 'Castel Gala' apple trees was studied as superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX). Also, hydrogen peroxide (H2O2) was quantified, as well as the efficiency of treatments for different concentrations of Erger®, garlic extract and Dormex® in inducing budbreak and flowering. Studied model took place in apple trees as „Baronesa‟, „Imperatriz‟, „Fuji Suprema‟, „Fred Hough‟ and „Lisgala‟. Nine years of phenological and climatic data were correlated and the efficiency of the following cold accumulation models were evaluated: Utah, Utah Modified, CH (Chilling Hours)<7,2 °C, CH<10 °C, CH<15 °C, Low chill, Taiwan low chill and Daily positive Utah chill unit (PCU). And the thermal sum models were: GDH (Growing Degree Hours) basis 4,5 °C, GDH basis 10 °C, GDH basis 15 °C, GDH (Anderson) basis 4,0, GDH (Anderson) basis 10,0, GU (Growing Units) 4,0/25, GDH 2,5/29, GU 2,5/29 and number of days. As the dormancy stage approaches the end, SOD enzyme activity increases, but this is not influenced by the inducers application. CAT enzyme activity decreases in most treatments. H2O2 levels were not influenced by the analysis data and treatments application, being Dormex® 1% + mineral oil 3% and Erger® 7% + calcium nitrate 5% the most efficient, and the latter was the best tested alternative inducer. Regarding chilling accumulation models, the following ones were considered efficient (coefficient of variation <15%), CH<15 °C, Taiwan low chill, Low chill and Utah Modified. When approaching the thermal sum models, the ones that showed greater constancy for having a low coefficient of variation in different stages and cultivars were GU 4.0/25 and GU 2.5/29. Models that use high base temperature (10 °C and 15 °C) have low efficiency when applied to apple trees, and the number of days model is highly efficient for harvest forecasting in regions that have historical harvest dates.