The effect of the presence of R‐genes for resistance to late blight (Phytophthora infestans) of potato (Solanum tuberosum) on the underlying level of field resistance

Abstract

The differential genotypes R 1 , R 10 and R 11 , as originally defined by Black, were crossed with R-gene-free cultivars and the progenies divided into two subpopulations comprising those which had inherited the R-gene and those which had not. The underlying level of field resistance of the two groups was compared in a field trial in which they were inoculated with an isolate that could overcome the relevant R-genes. The R-gene-bearing group was significantly ( P < 0·001) more resistant than the R-gene-free group, with mean scores over four dates in 2000 of 4·86 and 4·09, respectively, on a 1-9 scale of increasing resistance, and of 4·10 and 2·35 on one date in 2001. However, the magnitude of the effect depended on the R-gene and the year of the trial. Data from a progeny of cv. Stirling (with an R-gene and a high level of field resistance) were examined and the same effect of an R-gene found. Fewer of the R-gene-bearing group of clones were highly susceptible, and more were resistant. The most resistant clones always bore the R-gene. It is concluded that increased resistance is conferred by the defeated R-gene or linked genes for field resistance.

Tagging QTLs for late blight resistance and plant maturity from diploid wild relatives in a cultivated potato (Solanum tuberosum) background

“…In fact, some researchers speculate that major genes are just very eVective alleles at QTLs and that the borders between the two traditionally distinguished types of resistance can be blurred (Gebhardt and Valkonen 2001). Also, R genes overcome by pathogen can still have some residual eVect, enhancing the quantitative resistance of the plant (Stewart and Bradshaw 2001;Stewart et al 2003). QTLs for the resistance components and length of vegetation period in our study only partially overlapped (Fig.…”

Epidemiology and Integrated Control of Potato Late Blight in Europe

“…Although planted in small quantities, many of these would seem to have a stable, race-nonspecific resistance, but there is evidence that some have a combination of race-specific (R-gene) and horizontal resistance. Stewart et al (2003) suggested that increased resistance was conferred by defeated R-genes or linked genes for field resistance. In seasons and at locations where disease pressures remained low, these resistant varieties have been grown and have yielded well without protection and are therefore of interest to organic farmers, particularly if varieties have high levels of tuber-blight resistance.…”

Single Nucleotide Polymorphisms in the Allene Oxide Synthase 2 Gene Are Associated With Field Resistance to Late Blight in Populations of Tetraploid Potato Cultivars

“…Genetic analysis suggests that the defense mechanisms underlying both resistance phenotypes are similar. R genes as well as genes with sequence similarity to R genes, defense signaling genes as well as defense response genes, may play a role in quantitative resistance to P. infestans (Leonards-Schippers et al 1992, 1994Trognitz et al 2002;Stewart et al 2003;Pajerowska et al 2005;Tan et al 2008). Introgression of R genes from the wild species Solanum demissum into cultivated potato failed to equip cultivars with durable resistance in the field, because the HR type of resistance was soon overcome by new, virulent P. infestans races.…”