Population Dynamics, Effective Soil Factors, and LAMP Detection Systems for Phytophthora Species Associated with Kiwifruit Diseases in China

China has the largest area of kiwifruit production in the world. Pathogens associated with root diseases of kiwi trees have not been investigated extensively. In this research, three Phytophthora species, Phytophthora cactorum, Phytophthora cinnamomi, and Phytophthora lateralis, which are pathogenic to kiwi trees in the main planting areas of China, were studied. The population densities of these species in 128 soil samples from 32 kiwi orchards in 2017 and 2018 were measured using multiplex real-time quantitative PCR based on the ras-related protein gene Ypt1. P. cactorum was the most widely distributed of the three species in orchards of the Zhouzhi and Meixian prefectures. We used redundancy analysis to examine soil factors in the kiwi orchards to understand their effects on the population densities of the Phytophthora species. The redundancy analysis indicated that soil temperature and pH were significantly correlated with the abundance of P. cactorum and P. cinnamomi. In addition, two loop-mediated isothermal amplification detection systems for P. cactorum were developed based on the tigA gene. The color-change detection system proved to be accurate, sensitive, and faster than quantitative PCR. The results of this study, along with the loop-mediated isothermal amplification detection systems, will be of great use in the control of Phytophthora diseases for the production of kiwifruits in China.