Mating-Type and Sexual Differentiation of Phytophthora Colocasiae in Japan

Abstract In Japan, Phytophthora colocasiae causes the leaf blight of taro, which has resulted in huge losses since 2015. To investigate the causes of disease persistence and expansion, it is important to clarify the basic properties of this pathogen. We collected in total 317 P. colocasiae isolates from 99 fields in 7 prefectures during 2014 to 2020. The mating-type of each isolate was examined, and two or more isolates which were collected in single fields or taro leaves were selected to analyze the mating-type complexity. We found five kinds of mating types were identified: heterothallic A1 and A2, self-fertile (SF) A1, A2 and A1/A2 types, and a complex and diverse distribution of mating-types was present in one field or leaf. In addition, the stability of each mating-type was analyzed by single hyphae, zoospore and zoosporangium. The results suggested that the SF isolates were shown to be genetically unstable, while heterothallic isolates had a stable property. In the pathogenicity test of different mating-type isolates, heterothallic A1 isolates were less pathogenic than heterothallic A2 and SF isolates. However, there was no relationship between the pathogenicity and the growth rate on culture medium.