Abstract
BackgroundField resistance is often effective and durable as compared to vertical resistance. The introgression line (INGR15002) derived from O. glumaepatula has proven broad spectrum field resistance for both leaf and neck blast.ResultsQuantitative Trait Loci (QTL) analysis of INGR15002, led to the identification of two major QTL - qBL3 contributing about 34% and 32% phenotypic variance towards leaf and neck blast resistance, respectively and qBL7 contributing about 25% of phenotypic variance for leaf blast. Further, qBL3 was fine mapped, narrowed down to 300 kb region and a linked SNP maker was identified. By combining mapping with microarray analysis, a candidate gene, Os03g0281466 (malectin-serine threonine kinase), was identified in the fine mapped region and named as Pi68(t). The nucleotide variations in the coding as well as upstream region of the gene was identified through cloning and sequence analysis of Pi68(t) alleles. These significant variations led to the non-synonymous changes in the protein as well as variations (presence/absence) in four important motifs (W-box element; MYC element; TCP element; BIHD1OS) at promoter region those are associated with resistance and susceptible reactions. The effect of qBL3 was validated by its introgression into BPT5204 (susceptible variety) through marker-assisted selection and progeny exhibiting resistance to both leaf and neck blast was identified. Further, the utility of linked markers of Pi68(t) in the blast breeding programs was demonstrated in elite germplasm lines.ConclusionsThis is the first report on the identification and characterization of major effect QTL from O. glumaepatula, which led to the identification of a putative candidate gene, Pi68(t), which confers field resistance to leaf as well as neck blast in rice.
Highlights
Field resistance is often effective and durable as compared to vertical resistance
The present study focuses on understanding the genetics of resistance and identifying the gene(s) underlying the resistance mechanism
Mapping Quantitative Trait Loci (QTL) for Field Resistance to Leaf Blast Segregation ratios of F2 population for blast resistance showed continuous distribution, indicating the resistance in INGR15002 is quantitative in nature (Figure S1A)
Summary
Field resistance is often effective and durable as compared to vertical resistance. The introgression line (INGR15002) derived from O. glumaepatula has proven broad spectrum field resistance for both leaf and neck blast. Rice blast caused by Magnaporthe oryzae, is one of the most destructive diseases that affects the crop, right from the vegetative stage (leaf blast) to the reproductive stage (neck blast) (TeBeest et al 2007) causing up to 30% of crop loss annually, thereby threatening global food security (Sakulkoo et al 2018). Outbreak of this disease is a serious concern in many Asian and African countries, where the yield loss under epidemic conditions ranged from 60% to 100% (Kihoro et al 2013). Field resistance contributed by QTL offer horizontal or partial resistance, which is known for its durability in combating the disease out-breaks in a race non-specific manner (Fukuoka et al 2015)
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