Virulence Diversity Of Phytophthora Infestans On Potato In Northwest Of China

The heterothallic oomycete Phytophthora infestans is one of the most serious croppathogens. It causes the late blight which is a devastating disease on potato production. Potatois the main crop in Ningxia, Shaanxi and Gansu. Understanding the composition of virulenceand mating type distribution of the pathogen is essential for breeding of resistant varieties anddeployment of resistance genes.In this study, a total of146P. infestans isolates collected from northwest of China during2008to2011were examined for virulence diversity on a set of differential near-isogenic linescontaining R1to R11major resistance genes, respectively, by using detached leaf assay. Themain results include:1. A total of161P. infestans isolates were collected from Gansu in2010and157weredetermined for the mating type. Result showed that141isolates were A2mating type whilethe remaining16were A2mating type but self-fertile. No A1mating type isolates were found,indicating that the A2replaced A1and became the dominant mating type.2. Among22P. infestans isolates obtained from Northern Shaanxi in2009, only2pathotypes were identified, with the dominant pathotype3.4.10at a frequency of86%and the“super virulent” pathotype1.2.3.4.5.6.7.8.9.10.11that overcomes all11resistance genesexamined at a frequency of14%.3. In Gansu, virulence assay of15P. infestans isolates from2008and5from2009showed the presence of5pathotypes,3.10,3.4.10,3.4.6.8.10.11,3.4.6.8.9.10.11and the“super virulent” race. The first three pathotypes were only found in2008with the dominantpathotype3.4.10at a frequency of60%, and the remianing two were only detected in2009.4. A total of104P. infestans isolates from Ningxia, including41from potato fields in2009and63from a germplasm nursery in2009and2011, were examined for virulence. Theresult showed the presence of only five pathotypes,3.4.10,3.4.6.8.10.11,2.3.4.5.6.7.8.9.10.11,1.2.3.4.5.6.7.8.10.11and the “super virulent” race, with the latter as the dominant pathotype.In the germplasm nursery, most of the potato cultivars were heavily infected with P. infestansin both2009and2011, suggesting very limited disease resistance gene resources. 5. In conclusion, limited number of P. infestans pathotypes was detected in theexaminted regions. Both the pathotype3.4.10that contains only3virulence factors, and the“super virulent” race that overcomes R1to R11resistant genes, were detected in the threeprovinces.