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.
Highlights
Gray leaf spot (GLS), caused by Magnaporthe oryzae, in ryegrasses is a very serious problem
We have identified a locus for a GLS resistance gene, LmPi1, on linkage group (LG) 5 of Italian ryegrass [4] and performed targeted mapping of rice expressed sequence tags (ESTs) around the locus using a synteny-based comparative genomics approach [10]
Evaluation of GLS resistance in the F1 population We conducted two independent inoculations each for the second-youngest leaves still expanding and the thirdyoungest fully expanded leaves, which are hereafter referred to as young leaves and expanded leaves, respectively, in the F1 population
Summary
Gray leaf spot (GLS), caused by Magnaporthe oryzae (anamorph Pyricularia oryzae), in ryegrasses is a very serious problem. Infected small seedlings die within a matter of days, and stands of the grasses are seriously damaged by the disease. Italian ryegrass (Lolium multiflorum Lam.) originated in the Mediterranean region and is produced mainly for hay and silage. It is one of the most important forage grasses in the temperate zones of Europe and Asia because of its high palatability to and digestibility by livestock [1,2]. Blast disease, caused by the fungal pathogen Magnaporthe oryzae (anamorph Pyricularia oryzae), is the most. If M. oryzae heavily infects leaves of susceptible genotypes, the infected leaves die, and small seedlings are killed within a matter of days
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