REAÇÃO DE CULTIVARES DE GIRASSOL (Helianthus annuus) À Alternariaster helianthi

Abstract

Alternaria leaf spot (Alternariaster helianthi) is a very common disease in humid areas of the canopy of sunflower crops, in the lower leaves that influences the photosynthetic activity of many plants. The objective of this work was to study the reaction of sunflower varieties to alternaria leaf spot. In the city of Urutaí (GO), 14 genotypes were cultivated, in a design in four randomized blocks, measuring two x eight m. In each plot, 20 leaf samples were taken from the lower leaves, which had their severity quantified and their phenological stage evaluated. Five evaluations were performed at 53, 60, 67 and 74 days after planting (DAP) which served to calculate the area under the disease progress curve and infection rate. Parametric and non-parametric tests were used for statistical analysis. Statistically, at 53 DAP the most resistant genotypes were BRS G71, BRS G72, Aguará 06, Hélio 250, BRS G62, BRS G63, BRS G65 and BRS G69 belonging to stages R3 to R5.9 and severities from 0.99 to 1.59 % . At 74 DAP, the genotypes that showed the lowest severity of Alternaria leaf spot were BRS G62, BRS G63, Hélio 250, BRS G64, Aguará 06, BRS G67, BRS G66, BRS G69 and BRS G72, all belonging to stages R7- R9 presenting mean severity values ranging from 8 to 15%. Statistically, the genotype that showed the lowest infection rate was BRS G72, statistically differing from the others, presenting 0.38% day-1. The identification of genotypes resistant to alternaria leaf spot is an important strategy for integrated management of alternaria leaf spot in sunflower crops.