Identification And Breeding Potential Evaluation Of Loci For Root-Related Traits In Wheat

Root system architecture(RSA)is the key part of wheat to improve the resisitance to low phosphorus,salt and drought.Its genetic improvement is named as the second "green revolution" after "dwarf breeding".Parental reproductive environment(PRE)has certain influence on the growth and development of wheat RSA.Based on the genetic linkage map constructed using the wheat 55 K SNP array and the recombinant inbred lines population developed by crossing wheat lines 20828 and SY95-71,quantitative trait loci(QTL)of 11 traits related to RSA at seedling stage from five different PRE-seeds were identified.The identified flanking markers closely linked to the major QTL were transformed into kompetitive allelespecific PCR(KASP)markers,and their genetic effects were verified in different genetic backgrounds.Lines with or without positive alleles of target QTL were screened for evaluating their tolerance to abiotic stresses including low phosphorus,salt and drought.Further the utilization potential of major QTL in different environments was analyzed.By identifying the geographical distribution and effect of positive alleles for major QTL in Chinese wheat landraces,as well as their distribution and selection in Sichuan wheat landraces and Sichuan wheat cultivars,their utilization status in breeding was also evaluated.Excellent lines with breeding value were further selected according to agronomic traits and resistance to stripe rust from the mapping population.The identified major root traits-related loci,screened excellent lines with breeding value,and the developed closely-linked KASP markers in this study will contribute to cultivating lines with suitable RSA in the future,and thus lay the foundation for breeding wheat varieties.The main findings of this study are as follows:1.A total of 32 RSA related QTL were detected on 14 different chromosomes.Among them,eight major QTL controlling total root length,root area,root volume,root forks,root dry weight,shoot dry weight and maximum root length were identified.2.Major QTL QTrl.sicau-2SY-4D and QMrl.sicau-2SY-3D.2,which may be independent of PRE,were located on chromosome 4D and 3D,respectively.The genetic effects of major QTL were successfully verified in two populations with different genetic backgrounds based KASP markers transformed from closely linked flanking markers.3.Lines with or without positive allele of target QTL were screened.The relative value or phenotypic variation range of RSA traits for lines with positive alleles showed significant advantages compared with those of lines without positive alleles under low phosphorus,salt and drought conditions,indicating positive alleles of QTrl.sicau-2SY-4D and QMrl.sicau-2SY-3D.2 play roles in contributing to the tolerance to abiotic stresses.4.Positive allele of QTrl.sicau-2SY-4D was widely dstributed in Chinese wheat landraces.Its distribution pattern is signicantly associated with precipitation.It can significantly improve the phenotypic values of total root length,tiller number and spikelet number per spike(2.47%,5.54% and 1.50%,P<0.05),but significantly reduce thousand-grain weight(3.51%,P<0.01).Positive allele of QMrl.sicau-2SY-3D.2 has not been detected in Chinese wheat landraces and may be a rare allele.5.The distribution frequency of positive allele at QTrl.sicau-2SY-4D in Sichuan wheat landraces and Sichuan wheat cultivars was 45.61% and 53.94%,respectively.That of positive allele at QMrl.sicau-2SY-3D.2 in Sichuan wheat landraces and Sichuan wheat cultivars was 0%and 1.81%,respectively.The increase in the distribution frequency from wheat landraces to cultivars suggests that they were positively selected during wheat breeding in Sichuan.6.We further selected favorablelines in the mapping population according to the following criteria: tiller number >7.26,spikelet number per spike >23.53,thousand-grain weight >42.46 g,and stripe rust disease index <52.70.Five favorablelines(#3,#41~a,#53,#57 and #186)carrying positive allele of QTrl.sicau-2SY-4D and/or QMrl.sicau-2SY-3D.2 with better agronomic traits and certain resistance to stripe rust were screened.Their plant height and spike extension length were similar to their parents,and can be used in wheat breeding.Similarly,27 lines were screened from the validation population and natural population,and should have breeding potential although their plant architecture or resistance to stripe rust are yet to be evaluated.