Estágios foliares, fenologia da seringueira (Hevea spp.) e interação com Microcyclus ulei (mal das folhas)

Abstract

The rubber tree is a tropical species that loses its leaves periodically. This deciduifolio habit is an important character for the rubber tree, that is, clones uniform defoliation provides a reduction in the pathogens inocule whose reproductive structures are located in the old leaves. After defoliation, it occurs the foliar renewal and it is at this stage, also known as refoliation, that the rubber tree presents susceptible leaflets in which occur most part of the foliar deseases, such as leaf blight, where the cycle of the pathogen (Microcyclus ulei (P. Henn.)v. Arx) is straightly related with the foliar stages (B, C and D). Therefore, the knowledge on these stages, clones phenologic behavior, factors that influence this character and local climate conditions is important for their selection. The objectives of this work were: characterize through quantitative and descriptive foliar morphology the stages B, C and D; characterize the phenologic behavior and the incidence of South American Leaf Blight; correlate the beginning of the defoliation period with climatic parameters, and leaf blight incidence, during the foliar renewal period, with climatic parameters. For the stages characterization, it was used the clone PB 235, from which the leaves central leaflets were collected, at different stages. It was measured the foliolar limbus lenght, width and area, and the petiole lenght and diameter. It was also determined the form of the limbus, apex and base of the foliolar lamina, as well the leaf coloration. For the other objectives, the clones Fx 3844, Fx 3864, Fx 2261, IAN 873, IAN 717 and RRIM 600 of rubber trees from Vale do Ribeira region, São Paulo state were used, being the fallen leaflets collected weekly in four baskets by clone, randomly distributed. The leaflets were totalized, separated by age and analyzed as for the incidence of the fungus Microcyclus ulei (P. Henn.)v. Arx, during six years of evaluation. It was used adult plants with initial age of 8 years, distributed in clonal blocks of 500 plants each. The climatic variables (relative humidity, temperature, pluvial precipitation and evapotranspiration) used for mathematic models were daily collected, by using the averages for the correlation with the beginning of the defoliation period and with the clones desease incidence. From the results it was concluded that: a) the five quantitative morphological characters and the descriptive character and foliar limbus coloration permitted to differenciate the rubber tree foliar stages (B, C and D), in clone PB 235; b) in Vale do Ribeira/SP region, the change of leaves is uniform for clones IAN 873, Fx 2261, Fx 3844 and RRIM 600, variable for clone Fx3864 and irregular for IAN 717, and leaf blight presented low incidence in clones IAN 873, Fx 2261, Fx 3844, probably, due to their uniform behavior in the leaves change; c) it is noticed that the climatic parameters precipitation and minimum temperature have great correlation (R2 = 0.95) with the beginning of leaves change of the clones studied in Vale do Ribeira/SP region; d) the Leaf Blight Incidence Index (LBII), during the period of the rubber tree foliar change, can be foreseen by the mathematical models: Y = – 111.286413 + 22.854437m_eva + 5.085763mtmin + 1.670566murs90 (R2 = 0.72); Y = 343.774775 – 10.122495mti20 (R2 = 0.80).