OCCURRENCE OF ALTERNARIA spp. IN THE SEEDS OF BASIL AND ITS PATHOGENICITY

Abstract

Eighteen seed samples of basil, belonging to the cultivars most frequently grown in the Piedmont area for pesto production and obtained from farms affected by the disease in Piedmont during the fall of 2010 as well as from experimental lines of basil, were assayed for the presence of Alternaria spp., the causal agent of leaf spot of basil. Isolations were carried out by disinfected and not disinfected seeds. All eighteen tested samples resulted contaminated by Alternaria spp. and the frequency of isolation of Alternaria spp. colonies was higher in the case of not disinfected seeds for all samples tested. In the case of seeds belonging to experimental lines of basil, the frequency of isolation of Alternaria spp. was 1.18% from not disinfected seeds, and 0.43% from disinfected seeds. In the case of seeds belonging to commercial varieties of basil, Alternaria spp. was isolated respectively from 7.29% and 2.62% of not disinfected and disinfected seeds. When twenty-eight isolates of Alternaria spp. obtained from seeds of experimental lines of basil under development were tested for their virulence, 22 were able to infect basil leaves. Twenty of them, obtained from disinfected and not disinfected seeds, showed a good level of virulence, infecting more than 30% of leaves. One hundred eighty one isolates of Alternaria spp. strains were obtained from seeds of commercial varieties, of which 149 from not disinfected seeds and 32 from disinfected seeds. Out of 149 strains obtained from not disinfected seeds, 102 were virulent and 47 were not virulent. Only two isolates of Alternaria spp. out of 32 obtained by disinfected seeds were not virulent when tested on basil. This work provides evidence that Alternaria spp. the causal agent of leaf spot of basil, is seed-transmitted, which suggests that seeds may be important in disseminating the pathogen.