Fine Mapping Of QTLs For Pre-Harvest Sprouting Resistance In White-Grained Wheat

Pre-harvest sprouting(PHS)seriously affects wheat yield and quality,resulting in significant economic losses to agricultural production.Improving PHS resistance is one of the important goals of wheat breeding.Identification of the genes for PHS resistance and development of molecular markers closely linked with PHS resistance can help to multi-gene pyramiding breeding.In this study,the recombinant inbred population(RIL,228 lines)derived from a cross between the white-grained released variety Jimai 20(moderate PHS resistance)and the white-grained landrace Suiningtuotuo(high PHS resistance)was used to detect QTL associated with PHS resistanc by Inclusive Composite Interval Mapping method.The grain germination index(GI)and germination percentage(GP)of the RIL population were measured at 5 and 15 days after harvest in 2016 and 2017.Based on polymorphic SNP marker from Wheat 660 K SNP array between the two parents and two pools with significantly different PHS resistance,the CAPS markers were developed to narrowe down the target region.The main results are as follows:1.The GI and GP values showed a wide variation in the RIL population and a continuous normal distribution,and there was a significant correlation across environments.2.The two stable QTLs were detected on chromosomes 4AL and 2BS,designated Qphs-4AL and Qphs-2BS,and located within the interval wmc650-barc170 and gwm257-barc318,respectively.3.Based on the Wheat Axiom TM 660 K Arrays,a CAPS marker(AX-110710058-caps)was developed in the target region.Finally,the Qphs-4AL locus was narrowed to AX-110710058-barc170 with the physical interval of 606.5-607.8 Mb(about 1.3 Mb),explaining 0.92-9.81% of the phenotypic variation.The t-test showed there was a significant difference in PHS resistance between varieties carrying the two allelic variations of the CAPS marker in the RIL population and the natural population composed of 407 wheat varieties(lines).Therefore,our results provide useful information for cloning the candidate gene in the target region.4.Combining molecular markers analysis with sequencing methods,we found that the two reported genes associated with PHS resistance on chromosome 4AL,PM19-A1(604Mb)and Ta MKK3-A(609Mb),showed no polymorphisms between Jimai 20 and Suiningtuotuo and located outside the target region,indicating that the two genes are notthe candidates underlying the Qphs-4AL locus.Therefore,we suggest that there may be other genes controlling PHS resistance at the Qphs-4AL locus.Further researches are needed to confirm this speculation.5.Based on IWGS Ref Seq v1.0,three genes encoding flavin monooxygenase-like enzyme(FMO),ethanol dehydrogenase,and plant histidine phosphatase were predicated at the Qphs-2BS locus.A CAPS marker(YUCCA-2BS)was developed according to the SNP positioned at 591 bp of initiation codon of the YUCCA gene.Linkage analysis indicated that this gene was not within the target region using the RIL population from Jimai20/Suiningtuotuomai cross,suggesting that the other two genes encoding ethanol dehydrogenase and plant histidine phosphatase are possibly the candidates underlying the Qphs-2BS locus.