ABSTRACT:
Early blight is one of the most important fungal diseases of potato. The objective of this study was to evaluate the in vitro reaction of potato genotypes to the severity of early blight and compare the speciesAlternaria solani and Alternaria grandis , etiologic agents of disease, through the evaluation of physiological characteristics. Twenty-two genotypes of the Potato Breeding Program at UFLA, two cultivars, Aracy and Bintje, patterns of resistance and susceptibility, respectively were evaluated. For inoculation, three isolates ofA. grandis and two isolates ofA. solani were used. Plantlets obtained in vitro were inoculated with a 5mm diameter mycelial disk of isolatesAlternaria spp. of. These were incubated in severity and classified according to the rating scale. Isolates of Alternaria spp. were evaluated for mycelial growth index (MGI) and for formation of mycelial compatibility groups (MCG). The methodology for evaluating the in vitro reaction of genotypes to severity of early blight was efficient for both isolates. The isolates ofA. solani andA. grandis were similar in their aggressiveness. The isolates of A. grandis MGI's had higher, and therefore mycelium grew faster when compared to those isolated fromA. solani . The occurrence of mycelial compatibility among isolates of A. solani andA. grandis indicated the possible occurrence of parasexual cycle.
Key words:
Alternaria grandis; Alternaria solani; mycelial compatibility; aggressiveness; genetic resistance.
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