The relationship between plant growth and climatic conditions make possible to develop harvest forecast models. This work studied varieties of tangerines similar to Murcott tangor grafted on different rootstocks and evaluated for phenological response to accumulation of degree-days (DD). The experiment was conducted at the "Centro Avançado de Pesquisa Tecnológica do Agronegócio de Citros Sylvio Moreira/IAC", Cordeirópolis SP, during the 2003-04 season. The experiment was designed in random blocks in a factorial scheme of 5 (canopy cultivars) x 3 (rootstocks), with 4 replicates and one tree per plot. The studied varieties were: Thomas, Szuwinkon, Szuwinkon x Szinkon-Tizon, South Africa and the control Murcott tangor. These varieties were grafted on Rangpur lime, Sunki tangerine and Swingle citrumelo, planted in 1995. For the phenological characterization, grades were attributed according to a scale elaborated for the phenological stages, starting on the pre-flowering until the physiological maturation of the fruits. The determination of the dates of each reproductive phase in the studied plants was done. With that, it was possible to calculate the accumulation of degree-days for phenological sub-periods. According to the canopy/rootstock combinations there were differences in tree responses, such as: a) the accumulation of degree-days, from the anthesis to ratio 12, which varied from 2272 to 2836 DD; the Szuwinkon, Szuwinkon x Szinkon-Tizon and South Africa tangerines had the smallest requirement (<FONT FACE=Symbol>»</FONT> 2328 DD); the Murcott tangor, intermediate (<FONT FACE=Symbol>»</FONT> 2462 DD); and the Thomas tangerine, the largest (<FONT FACE=Symbol>»</FONT> 2791); it was observed 20 days of differences from flowering to ratio 12, depending of canopy/rootstock combination.
citrus; rootstocks; phenology; grades of scale; degree-days
