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Panicle blast 1 (Pb1) resistance is dependent on at least four QTLs in the rice genome.

ABSTRACT: Rice blast is the most serious disease afflicting rice and there is an urgent need for the use of disease resistance (R) genes in blast tolerance breeding programs. Pb1 is classified as a quantitative resistance gene and it does not have fungal specificity. Pb1-mediated resistance develops in the latter stages of growth. However, some cultivars, such as Kanto209 (K209), cultivar name Satojiman, despite possessing Pb1, do not exert resistance to rice blast during the reproductive stage.We found that the expression of WRKY45 gene downstream of Pb1 was weakly induced by rice blast inoculation at the full heading stage in K209. Genetic analysis using the SNP-based Golden Gate assay of K209 crossing with Koshihikari Aichi SBL (KASBL) found at least four regions related to the resistance in the rice genome (Chr8, Chr9, Chr7, Chr11). Mapping of QTL related to Chr7 confirmed the existence of factors that were required for the resistance of Pb1 in the 22 to 23 Mbp region of the rice genome.We clarified how the K209 cultivar is vulnerable to the blast disease despite possessing Pb1 and found the DNA marker responsible for the quantitative resistance of Pb1. We identified the QTL loci required for Pb1-mediated resistance to rice panicle blast. Pb1 was negatively dependent on at least three QTLs, 7, 9 and 11, and positively dependent on one, QTL 8, in the K209 genome. This finding paves the way for creating a line to select optimal QTLs in order to make use of Pb1-mediated resistance more effectively.

SUBMITTER: Inoue H

PROVIDER: S-EPMC5539066 | biostudies-other | 2017 Dec

REPOSITORIES: biostudies-other

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Project description:BackgroundRice blast, caused by the fungus Pyricularia oryzae, represents the most damaging fungal disease of rice worldwide. Utilization of rice resistant cultivars represents a practical way to control the disease. Most of the rice varieties cultivated in Europe and several other temperate regions are severely depleted of blast resistance genes, making the identification of resistant sources in genetic background adapted to temperate environments a priority. Given these assumptions, a Genome Wide Association Study (GWAS) for rice blast resistance was undertaken using a panel of 311 temperate/tropical japonica and indica accessions adapted to temperate conditions and genotyped with 37,423 SNP markers. The panel was evaluated for blast resistance in field, under the pressure of the natural blast population, and in growth chamber, using a mixture of three different fungal strains.ResultsThe parallel screening identified 11 accessions showing high levels of resistance in the two conditions, representing potential donors of resistance sources harbored in rice genotypes adapted to temperate conditions. A general higher resistance level was observed in tropical japonica and indica with respect to temperate japonica varieties. The GWAS identified 14 Marker-Traits Associations (MTAs), 8 of which discovered under field conditions and 6 under growth chamber screening. Three MTAs were identified in both conditions; five MTAs were specifically detected under field conditions while three for the growth chamber inoculation. Comparative analysis of physical/genetic positions of the MTAs showed that most of them were positionally-related with cloned or mapped blast resistance genes or with candidate genes whose functions were compatible for conferring pathogen resistance. However, for three MTAs, indicated as BRF10, BRF11-2 and BRGC11-3, no obvious candidate genes or positional relationships with blast resistance QTLs were identified, raising the possibility that they represent new sources of blast resistance.ConclusionsWe identified 14 MTAs for blast resistance using both field and growth chamber screenings. A total of 11 accessions showing high levels of resistance in both conditions were discovered. Combinations of loci conferring blast resistance were identified in rice accessions adapted to temperate conditions, thus allowing the genetic dissection of affordable resistances present in the panel. The obtained information will provide useful bases for both resistance breeding and further characterization of the highlighted resistance loci.

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Panicle blast 1 (Pb1) resistance is dependent on at least four QTLs in the rice genome.

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