Phenological cycle and thermal accumulation in the genotypes of sweet orange in Southern Brazil

Abstract

Abstract The aim of this work was to study the phenology of several sweet orange cultivars and their relationship with the accumulated degree-day (ADD), under the conditions of the Depressão Central of Rio Grande do Sul, in Southern Brazil. For this, 25 genotypes were evaluated for three consecutive growing seasons between 2015 and 2018. The experiment was carried out in a Citrus Collection located in municipality of Eldorado do Sul, RS, Brazil. The ADD was calculated for each interval between the phenological stages, as well as for the entire cycle. The first one, swelling of the buds, was concentrated between mid-July and early August. Sprouting in winter increased the risk of frost damage. Full bloom occurred between August 28 and September 22, when the orange trees ‘Cabula’, ‘Rubi’, ‘Lima Verde’ and ‘Folha Murcha’ were the first to bloom and ‘Sanguinea’, ‘Salustiana’, ‘Midknight’ and ‘Jaffa’ the last. The last stage evaluated, the skin color change of the fruits, occurred between the beginning of April and the end of May, with 2,306.4 to 2,619.4 ADD, since the beginning of sprouting. The orange trees showed different behavior when compared between genotypes and between years. Two groups of cultivars were defined: early and late.