Dhr. Jun Guo: Avirulence genes in the potato late blight pathogen Phytophthora infestans

Avirulence genes in the potato late blight pathogen Phytophthora infestans 

Potato late blight, caused by the oomycete pathogen Phytophthora infestans, is the most disastrous disease on potato worldwide and also the greatest threat to potato production in China. To combat the disease, breeders have introduced late blight resistance (R) genes from various Solanum species into the cultivated potato. The proteins encoded by these R genes can recognise effector proteins that are produced by specific races of the pathogen. These effectors are encoded by avirulence (Avr) genes. In the field, however, potato cultivars can rapidly loose resistance due to rapid adaption of the pathogen. Key to a better understanding of the molecular basis of resistance to late blight is the unravelling of R protein-effector interactions. Hence, cloning of more R and Avr genes is a prerequisite to study these interactions.
 
This thesis describes the mapping and cloning of Avr genes in P. infestans, in particular of Avr1 and Avr4, and the phenotypic and genotypic diversity in P. infestans field isolates collected in Northern China. Genetic linkage mapping and transcriptome profiling were performed to find markers linked to Avr genes. The markers were then used to isolate the Avr4 gene and to identify seven candidates for the Avr1 gene within a 700 kb region on the P. infestans genome. Avr genes appear to be the most rapidly evolving genes in the genome of P. infestans and this may explain the high virulence diversity that is often found in the field, also in Northern China. Generating potato cultivars that can resist the many different races of P. infestans seems to be more challenging than anticipated.

Thesis: “Phytophthora infestans avirulence genes; mapping, cloning and diversity in field isolates”