QTL mapping of powdery mildew resistance in WI 2757 cucumber (Cucumis sativus L.)

Abstract

Powdery mildew (PM) is a very important disease of cucumber (Cucumis sativus L.). Resistant cultivars have been deployed in production for a long time, but the genetic mechanisms of PM resistance in cucumber are not well understood. A 3-year QTL mapping study of PM resistance was conducted with 132 F2:3 families derived from two cucumber inbred lines WI 2757 (resistant) and True Lemon (susceptible). A genetic map covering 610.4 cM in seven linkage groups was developed with 240 SSR marker loci. Multiple QTL mapping analysis of molecular marker data and disease index of the hypocotyl, cotyledon and true leaf for responses to PM inoculation identified six genomic regions in four chromosomes harboring QTL for PM resistance in WI 2757. Among the six QTL, pm1.1 and pm1.2 in chromosome 1 conferred leaf resistance. Minor QTL pm3.1 (chromosome 3) and pm4.1 (chromosome 4) contributed to disease susceptibility. The two major QTL, pm5.1 and pm5.2 were located in an interval of ~40 cM in chromosome 5 with each explaining 21.0-74.5 % phenotypic variations. Data presented herein support two recessively inherited, linked major QTL in chromosome 5 plus minor QTL in other chromosomes that control the PM resistance in WI 2757. The QTL pm5.2 for hypocotyl resistance plays the most important role in host resistance. Multiple observations in the same year revealed the importance of scoring time in the detection of PM resistance QTL. Results of this study provided new insights into phenotypic and genetic mechanisms of powdery mildew resistance in cucumber.

Research Article Molecular mapping and candidate gene analysis for resistance to powdery mildew in Cucumis sativus stem.

“…However, Shanmugasundarum et al (1971) differentiated between hypocotyl and leaf resistance and concluded that a recessive gene for hypocotyl resistance (pm-h) is essential for overall resistance. He et al (2013) and Walters et al (2001) also showed that a single-recessive gene (pm-h) controls hypocotyl resistance, and the role of a single gene in resistance is supported by other studies (Zhang et al, 2004;Liu et al, 2008a). By contrast, some studies reported that resistance is controlled by a pair of incomplete recessive genes and two pairs of epistatic genes (Shanmugasundarum et al, 1971;Mao et al, 2005).…”

“…The new primers and 10 pairs of SSR primers published by He et al (2013) were first used to screen for polymorphisms in the parents. Then, selected primers were used in the F 2 population to determine whether or not they were linked to the pm-s gene.…”

“…Four of these and three of 10 pairs of SSR primers published by He et al (2013) showed polymorphisms among the parents and were used to analyze the F 2 mapping population. Then, a new linkage group was constructed with 17 SSR primers, and a total length of 20.4cM (see Table 2 for names and sequences of the primers).…”

“…Hofstede et al (2008) andde Ruiter et al (2008) identified two linked PM resistance QTLs, pm-l and pm-h, conferring leaf resistance and hypocotyl resistance, respectively. He et al (2013) defined six genomic regions in four chromosomes that harbored QTLs for PM resistance, and among them was QTL pm5.2 for hypocotyl resistance. Zhang (2006) and Zhang et al (2004Zhang et al ( , 2007 reported AFLP markers linked to both resistant and susceptible genes for PM in cucumber, at genetic distances of 5.6 and 7.0cM, respectively.…”

“…Zhang (2006) and Zhang et al (2004Zhang et al ( , 2007 reported AFLP markers linked to both resistant and susceptible genes for PM in cucumber, at genetic distances of 5.6 and 7.0cM, respectively. Zhang et al (2008) and He et al (2013) reported SSR markers linked to resistant genes for powdery mildew in cucumber, at genetic distances of 2.6 and 13.0cM. However, there are no reports on chromosomal mapping for PM resistance in the cucumber stem (pm-s, a singlerecessive nuclear gene), and no reports on any molecular markers tightly linked to pm-s.…”