Fine mapping of a strong QTL of field resistance against rice blast, Pikahei-1(t), from upland rice Kahei, utilizing a novel resistance evaluation system in the greenhouse

Abstract

Field resistances (FR) against rice blast are highly evaluated by breeders for their durability, in contrast to the conspicuous but often less durable true resistances. However, lack of efficient systems for evaluation of resistance has delayed their practical application. Kahei, an upland domestic cv., is known for its very high FR against rice blast. We fine-mapped its highest quantitative trait loci (QTL), qBFR4-1, using residual heterozygosity of recombinant inbred lines (RILs) and our semi-natural rice blast inoculation/evaluation system in the greenhouse, with comparable accuracy to the true resistance genes. This system enabled reproducible high-density infection, and consequently allowed quantification of the resistance level in individual plants. The target region was first narrowed down to about 1 Mb around at 32 Mb from the top of chromosome 4 in the Nipponbare genome, with the upland evaluation system assessing the F7 generation of Koshihikari (lowland, FR: very weak) x Kahei (upland, FR: very strong) RILs. Then, F9 plants (4,404)--siblings of hetero F8 plants at the region--were inoculated with rice blast in a greenhouse using the novel inoculation system, and individual resistance levels were diagnosed for fine QTL analysis and graphical genotyping. Thus, the resistance gene was fine-mapped within 300 kb at 31.2-31.5 Mb on chromosome 4, and designated Pikahei-1(t). By annotation analysis, seven resistance gene analog (RGA) ORFs of nucleotide-binding-site and leucine-rich-repeat (NBS-LRR)-type were found in the center of the region as the most likely candidate counterparts of the resistance gene. This is similar in structure to the recently reported Pik cluster region, suggesting that most of the other dominant QTLs of the FRs may have similar RGA structures.

Fine Mapping of HWC2, a Complementary Hybrid Weakness Gene, and Haplotype Analysis Around the Locus in Rice

“…Recently, two blast resistance gene have been mapped proximal to the HWC2 locus: (1) a strong quantitative trait locus of field rice blast resistance named Pikahei-1(t) from upland rice cultivars Kahei cosegregated with RM5473 and mapped within 300 kb (Xu et al 2008). (2) A blast field resistance gene Pi39(t) from Chubu 111 cosegregated with RM5473 and RM3843 (Terashima et al 2008).…”

A novel blast resistance locus in a rice (Oryza sativa L.) cultivar, Chumroo, of Bhutan

“…There is no report of a true resistance gene in this region, whereas the presence of two field resistance genes has been reported. Pi39(t) and Pikahei-1(t) are located on the terminal part of the long arm of chromosome 4 and these are tightly linked with RM5473 (Terashima et al 2008;Xu et al 2008). Rice variety Mineharuka, with Pi39(t), was susceptible to some blast races and developed the same type of blast lesions as susceptible cultivars (Terashima et al 2008).…”

Mapping of a QTL for Field Resistance to Blast (Pyricularia oryzae Cavara) in Ingngoppor-tinawon, a Rice (Oryza sativa L.) Landrace from the Philippines

“…When we began this experiment, the dominant gene Pi39 was the most effective and well-characterized of the resistance QTLs located near qBFR4 (Xu et al 2008, Terashima et al 2008, Fukuoka & Okuno 2001, Miyamoto et al 2001, Kato et al 2002. Recently, a QTL derived from a wild relative (Oryza rufipogon) was also detected in a similar position (Hirabayashi et al 2010).…”

“…To develop blast-resistant varieties, researchers have sought rice blast-resistant genes, more than 90 of which have been reported (Miah et al 2013). Japanese upland rice varieties are known to be potential sources of blast resistance, and several quantitative trait loci (QTLs) have been identified from such varieties, including pi21 and qBR4-2 from 'Owarihatamochi' (Fukuoka & Okuno 2001, Fukuoka et al 2012, Pi34 in 'Chubu 32' from 'Sensho' (Zenbayashi et al 2002, Zenbayashi-Sawata et al 2005, Zenbayashi-Sawata et al 2007) and other QTLs from 'Kahei' (Xu et al 2008, Miyamoto et al 2001, 'Sensho' (Kato et al 2002) and 'Upland Rice Variety Norin 12' (Sato et al 2006). Recently, pi21 has been cloned by map-based cloning (Fukuoka et al 2009).…”