Phytophthora infestans , the causal agent of potato and tomato late blight disease continues to be a serious threat in almost all potato and tomato growing areas around the world, with dramatic and disastrous economic consequences. In Mauritius, the disease is reported every year and many of the commercial potato varieties (Spunta, Delaware and Mondial) previously found to be moderately resistant or susceptible to the disease, have now become highly susceptible. This study reports the first phenotypic and genotypic characterization of local strains of Phytophthora infestans from the island of Mauritius. Seven isolates of Phytophthora infestans were collected from distinct geographical areas during the blight seasons of 2012 and 2013 and tested for aggressiveness on four potato and three tomato cultivars, metalaxyl sensitivity and subjected to isozyme analysis at the Gpi and Pep loci. Results show that all the isolates exhibited a clear host adaptation to potato, being only very weakly pathogenic on tomato. Most of the isolates (five out of seven) had high or intermediate metalaxyl resistance. Isozyme analysis revealed that at the Gpi locus, two isolates were 86/86, one isolate was 86/100, one isolate was 100/100 and one isolate was 122/122. At the Pep locus, two isolates were 92/92, two isolates were 92/100 and three isolates were 100/100. The combined results of the tests indicate that the seven isolates collected over the island are genetically distinct from each other and do not represent the same strain.
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