Can the QTL for late blight resistance on potato chromosome 5 be attributed to foliage maturity type?

Abstract

We investigated the association between late blight resistance and foliage maturity type in potato by means of molecular markers. Two QTLs were detected for foliage resistance against Phytophthora infestans (on chromosomes 3 and 5) and one for foliage maturity type (on chromosome 5). The QTL for resistance to late blight and the QTL for foliage maturity type on chromosome 5 appeared to be mapped on indistinguishable positions. We were interested whether this genetic linkage was due to closely linked but different genes, or due to one (or more) gene(s) with pleiotropic effects. We therefore developed an approach to detect QTLs, in which resistance to late blight was adjusted for foliage maturity type. This analysis revealed the same two QTLs for resistance against P. infestans, but the effect of the locus on chromosome 5 was reduced to only half the original effect. This is a strong indication that the two indistinguishable QTLs for foliage maturity type and for late blight resistance on chromosome 5 may actually be one gene with a pleiotropic effect on both traits. However, there was still a significant effect on resistance against P. infestans on the locus on chromosome 5 after adjusting for foliage maturity type. Therefore we cannot rule out the presence of two closely linked QTLs on chromosome 5: one with a pleiotropic effect on both late blight resistance and foliage maturity type, and another with merely an effect on resistance. In addition, the two QTLs for resistance to late blight showed an important epistatic interaction, suggesting that QTLs for resistance affect each other's expression.

Tomato early blight (Alternaria solani): the pathogen, genetics, and breeding for resistance

“…In potato therefore about half the genotypic variation for EB resistance is also linked to maturity; still, this may be due to either close linkage or to pleiotropic effects. A very similar situation occurs in the potato-late blight (Phytophthora infestans) interaction (Visker et al 2003).…”

The novel, major locus Rpi-phu1 for late blight resistance maps to potato chromosome IX and is not correlated with long vegetation period

“…The few QTLs for vegetation period length tagged in population 97-30 are in accordance with published data. The most important QTL for vegetation period length has been repeatedly identiWed on potato chromosome V in the vicinity of the R1 locus and overlapped with QTL for late blight resistance (Collins et al 1999;Oberhagemann et al 1999;Bormann et al 2004;Bradshaw et al 2004;Visker et al 2003Visker et al , 2005. QTLs for vegetation period length on chromosomes IV, VIII and IX have also been detected in the QTLs tagging experiment of Bormann et al (2004).…”

“…The negative correlation between vegetation period length and resistance to P. infestans in potato was already reported in the 1950s (Jwieryjski 1990) and was explained by concomitant introduction of S. demissum genetic factors controlling resistance, both R genes and quantitative resistance loci (QRL), and vegetation period length into the cultivated potato gene pool. Quantitative trait locus (QTL) analysis of late blight resistance and vegetation period length in the same mapping populations could not distinguish whether the correlation between these two traits is due to close genetic linkage between functionally unrelated genes and therefore linkage drag, or to pleiotropic eVects of the same gene underlying both traits (Bormann et al 2004;Collins et al 1999;Oberhagemann et al 1999;Visker et al 2003Visker et al , 2005.…”

Genetic linkage of QTLs for late blight resistance and foliage maturity type in six related potato progenies

“…Leonards-Schippers et al, 1994;Meyer et al, 1998), of which the joint results suggest that all 12 potato chromosomes may harbour one or more QTLs for this trait (Gebhardt & Valkonen, 2001;Simko, 2002). Some of these studies have also identified QTLs for foliage maturity type, which are fewer in number, but coincide all with QTLs for resistance to late blight (Collins et al, 1999;Oberhagemann et al, 1999;Ewing et al, 2000;Visker et al, 2003). This touches on a further complication in breeding for resistance against P. infestans: the association of race-non-specific resistance with late foliage maturity (Toxopeus, 1958).…”

“…The most important QTL for both traits is located on chromosome 5 near marker GP21: the alleles that provide foliage resistance to late blight also provide late foliage maturity (Collins et al, 1999;Oberhagemann et al, 1999;Visker et al, 2003;Bormann et al, 2004;Bradshaw et al, 2004). However, phenotypic evaluations of race-non-specific resistance against P. infestans and of foliage maturity type in a set of test crosses indicated that some selection for resistance without affecting foliage maturity type should be possible (Visker et al, 2004).…”