Grouping sunflower genotypes by reaction to alternaria leaf spot (Alternaria helianthi) and yield.

The objective of this paper was to group sunflower genotypes based on the reaction to Alternaria leaf spot disease, yield and 1000-seed weight, using the multivariate method of Principal Component Analysis (PCA). Forty-nine sunflower genotypes were evaluated on field experiments, in Londrina, state of Parana, Brazil, during 2003/2004, 2004/2005, 2005/2006, 2007/2008 e 2008/2009 growing seasons. Alternaria disease severity, under natural conditions in the field, was evaluated at the R3 growth stage with reference to a diagrammatic scale developed for this disease. After harvesting, yield (kg ha-1) and 1000-seed weight (g) were also evaluated. The method of PCA was useful for grouping sunflower genotypes as a function of the studied variables. Genotypes with desirable agronomic characteristics (high yield and high resistance or tolerance to disease) are placed in the first quadrant. Less productive sunflowers are located in the third quadrant. Since no complete resistance to Alternaria leaf spot has been observed yet on sunflower genotypes, efforts to obtain cultivars with higher level of resistance should be continued