The adaptability of Phytophthora sojae to different types of soil determines the distribution of Phytophthora root rot of soybean in Heilongjiang Province of China

To understand the key soil factors that affect the survival and reproduction of Phytophthora sojae in soil, the number of zoospores and oospores of P. sojae and the cumulative incidence of Phytophthora root rot (PRR) in six major soil types were investigated. The soil samples which be collected from six representative sites in Heilongjiang Province of China were placed in the buckets, inoculated with P. sojae , and sown with a susceptible soybean variety, Sloan. The numbers of zoospores and oospores of P. sojae in the soil were affected by the soil type, which in turn affected the incidence of PRR of soybean. Of the six types of soil, the number of zoospores in black soil was the highest, and the cumulative incidence of PRR in black soil was also the highest. Further analysis of the correlation between the number of zoospores and the soil physicochemical properties showed that the number of zoospores and the cumulative incidence of PRR were both positively correlated with the soil monthly average relative moisture (MARM). It can be concluded that the soil type affects the asexual reproduction of P. sojae and the incidence of PRR mainly through the soil water-holding capacity; hence, the soil water-holding capacity determines the distribution of PRR. This finding not only provides a better understanding of the relationship between soil types and PRR occurrence but also provides a guidance regarding the optimal soil environment for soybean planting, e.g. try to avoid growing soybeans in black soil.