Virulence Complexity and High Levels of Fungicide Resistance Suggest Population Change of Phytophthora infestans in the Heilongjiang Province of China

Samples of Phytophthora infestans were isolated from 12 city and county fields in the main potato production areas of Heilongjiang province of China between 2004 and 2008. A total of 72 isolates were tested for virulence on a potato R gene differential set and 39 of these isolates were also analysed for their resistance to the fungicide metalaxyl. All 11 differential plants were infected by one or more of the isolates collected; the most commonly overcome differentials were R1, R3, R4, R7, R10, and R11. Most (89.7%) of the tested isolates were resistant to metalaxyl and the rest (10.3%) were sensitive. The proportion of metalaxyl-resistant isolates differed between sites (χ ²?=?25.42, df?=?10, p?χ ²?=?4.63, df?=?4, p?>?0.05). Taken together and in comparison with earlier pathogen population studies, our findings suggest that the population of P. infestans in Heilongjiang is different from that existing in the province two decades ago and that at various locations within the province, the new population has a high frequency of resistance to metalaxyl.