Differential pathogenicity on potato and tomato of Phytophthora infestans US-8 and US-11 strains isolated from potato and tomato
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Thirty-two isolates of Phytophthora infestans from potato and tomato tissues (US-11 strain, 8 isolates from potato and 6 from tomato; US-8 strain, 11 from potato and 7 from tomato), collected in Canada in 1997 and 1998 were tested for their differential pathogenicity on four potato and four tomato cultivars. This study clearly showed that US-8 and US-11 strains, representing the two main genotypes found in Canada since 1996, can both infect the foliage of potato and tomato plants. US-11 isolates from potato infected both tomato and potato at similar levels. Conversely, US-8 from potato caused lower colonization levels on tomato than on potato. Regardless of the host origin, it was found that US-8 and US-11 cause similar levels of colonization on potato, while US-11 isolates are more aggressive than US-8 on tomato. Thus, the genotype identity of a P. infestans isolate may inform us about its pathogenicity potential on the two hosts. Such information might be helpful towards time and space management of late blight caused by P. infestans, especially when these two crops are cultivated close to each other, or when other solanaceae species are growing nearby.