Identification and mating type determination of Phytophthora strains causing blight on two cucurbit crops in South China

To clarify mating types of the pathogen causing phytophthora blight on cucurbit crops, over 400 samples of affected wax gourd and cucumber plants were collected from nine cities in South China during 2007-2010. A total of 198 Phytophthora strains were isolated from the samples and identified as Phytophthora melonis based on their morphological characteristics and rDNA-ITS (internal transcribed spacer) sequences. Mating types of the strains were determined based on mating reactions between a field strain and each of the reference strains of mating types A1 and A2. Five mating types were found in the samples collected. The A0 mating type was predominant in Guilin city, representing 40.9 % of the strains obtained, while the A2 mating type was dominant in the sampling areas with a frequency of 37.5-66.7 %. The A0, A2 and A1A2 mating types were isolated from both hosts. The A1 and A1,A2 mating types were obtained only from the wax gourd and cucumber plants, respectively. The ratio of A1 and A2 mating types isolated from Guilin was close to 1:1, suggesting a possibility for sexual reproduction to occur in South China.