Phytophthora capsici on vegetable hosts in South Africa: distribution, host range and genetic diversity

摘要

The oomycete Phytophthora capsici is an economically important plant pathogen worldwide. Not much is known about this pathogen in South Africa. Therefore, the first aim of the study was to obtain a better understanding of the host range and distribution of the pathogen. Second, South African P. capsici isolates were characterised through mating-type tests and genotyping with eight microsatellite markers (simple sequence repeat markers (SSR)) that were developed from the draft genome sequence. Analyses of diseased samples from 2000 to 2008 showed that P. capsici was present in at least five provinces on cucurbitaceous (Cucumis melo and Cucurbita spp.) and solanaceous (Capsicum spp. and Lycopersicon esculentum) crops. Mating-type analyses of 78 isolates collected from these hosts showed that both mating types were present in all the sampled production regions. The mating-type frequency in the total South African population did not deviate significantly from a 1 : 1 ratio. Microsatellite genotyping of the isolates revealed that genotypic diversity was high in all regional populations with 59 of 78 isolates representing unique SSR multilocus genotypes (MLG). The remaining 19 isolates consisted of eight MLG that each included two to three isolates with identical SSR alleles. These identical isolates were considered to be clones that were derived from asexual reproduction due to significant P-SEX < 0.003 and P-SEX(f) < 0.008 probability values. Clonal genotypes were identified within and between production regions (Limpopo and Mpumalanga), on different crops (bell pepper, piquante pepper and tomato) and across years.