Identification of a novel major locus for gray leaf spot resistance in Italian ryegrass (Lolium multiflorumLam.)

Abstract

BackgroundGray leaf spot (GLS), caused by Magnaporthe oryzae (anamorph Pyricularia oryzae), in ryegrasses is a very serious problem. Heavily infected small seedlings die within a matter of days, and stands of the grasses are seriously damaged by the disease. Thus, the development of GLS-resistant cultivars has become a concern in ryegrass breeding.ResultsPhenotypic segregations in a single cross-derived F1 population of Italian ryegrass (Lolium multiflorum Lam.) indicated that the GLS resistance in the population was possibly controlled by one or two dominant genes with 66.5–77.9% of broad-sense heritability. In bulked segregant analyses, two simple sequence repeat (SSR) markers, which have so far been reported to locate on linkage group (LG) 3 of Italian ryegrass, showed specific signals in the resistant parent and resistant bulk, indicating that the resistance gene locus was possibly in the LG 3. We thus constructed a genetic linkage map of the LG 3 covering 133.6 centimorgan with other SSR markers of the LG 3 of Italian ryegrass and grass anchor probes that have previously been assigned to LG 3 of ryegrasses, and with rice expressed sequence tag (EST)-derived markers selected from a rice EST map of chromosome (Chr) 1 since LG 3 of ryegrasses are syntenic to rice Chr 1. Quantitative trait locus (QTL) analysis with the genetic linkage map and phenotypic data of the F1 population detected a major locus for GLS resistance. Proportions of phenotypic variance explained by the QTL at the highest logarithm of odds scores were 61.0–69.5%.ConclusionsA resistance locus was confirmed as novel for GLS resistance, because its genetic position was different from other known loci for GLS resistance. Broad-sense heritability and the proportion of phenotypic variance explained by the QTL were similar, suggesting that most of the genetic factors for the resistance phenotype against GLS in the F1 population can be explained by a function of the single resistance locus. We designated the putative gene for the novel resistance locus as LmPi2. LmPi2 will be useful for future development of GLS-resistant cultivars in combination with other resistance genes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0303-6) contains supplementary material, which is available to authorized users.

Pooled DNA sequencing to identify SNPs associated with a major QTL for bacterial wilt resistance in Italian ryegrass (Lolium multiflorum Lam.)

“…BSA to link DNA markers to a trait of interest was first proposed in 1991 (Michelmore et al) and has since been applied in forage grasses to determine linkage of the leafy head ( ldh 1 ) mutation to AFLP markers in Italian ryegrass (Gao et al 2002 ), to identify SSR or AFLP markers associated with resistance to crown rust ( Puccinia coronata f. sp lolii ) in perennial ryegrass (Dumsday et al 2003 ; Fujimori et al 2004 ; Muylle et al 2005 ), to link EST-derived CAPS and AFLP markers to a gene conferring resistance to ryegrass blast caused by Pyricularia spp. (Miura et al 2005 ) or to identify a novel major locus for gray leaf spot ( Magnaporthe oryzae ) resistance in Italian ryegrass (Takahashi et al 2014 ). BSA has been shown to work best for traits controlled by a single locus or gene, causing a distinct phenotype that allows a correct pool assignment.…”

Genomics Applied to the Analysis of Flowering Time, Abiotic Stress Tolerance and Disease Resistance: A Review of What We Have Learned in Lolium spp.

“…The first signs of gray leaf spot disease are small brown spots on leaves and stems that develop in water-soaked spots, followed by circular or oval lesions with gray midpoints and dark-brown margins. In cases of heavy infection, under warm and humid conditions and in particularly susceptible genotypes, the infected leaves die, and whole seedlings may be killed in a few days [138].…”

“…From the perspective of the development of GLS resistance, two major QTLs, LmPi1 and LmPi2, were identified in L. multiflorum [138]. Based on a BLASTX analysis, the two allelic forms of LmPi1 showed high similarity to parts of the HvAS1 and HvAS2 barley genes encoding asparagine synthetase.…”

DNA markers for Typhula resistance in timothy (Phleum pratense L.)

“…With BSA, DNA markers tightly linked with genes underlying monogenic traits or major genes underlying quantitative traits can be found. BSA has been used to uncover resistance genes in several crop species (Muyelle et al 2005, Han et al 2014, Takahashi et al 2014, including polyploids (Zhang et al 2014, Wang et al 2016 and also using dominant markers (Asnaghi et al 2004). MAS has also successfully been applied in breeding programs for transferring resistance loci in different crops (Farokhzadeh and Fakheri 2014).…”