An Accurate In Vitro Assay for High-Throughput Disease Testing of Phytophthora infestans in Potato.

An in vitro inoculation assay was developed as a routine disease testing method to study gene-for-gene interactions in the potato (Solanum tuberosum)-Phytophthora infestans pathosystem. The specificity and reliability of the new method was compared with the well-established detached-leaf assay. Four P. infestans isolates were tested for avirulence on a set of R gene differentials using tissue cultured plantlets and detached leaves. Both methods gave identical conclusions on avirulence profiles of all isolates. A population of 93 clones was phenotyped for segregation of two closely linked and functionally distinct genes-R3a and R3b-in the R3 locus. Both methods resulted in phenotypic scorings that were in perfect agreement for all clones. Furthermore, the phenotyping of the population was fully consistent with the genotyping obtained from analysis of molecular markers that flank each gene. This new assay is quick, space-effective, and accurate and can be used for investigation of the qualitative interaction between potato and P. infestans.