Screening Of Saline-Alkaline Tolerant Varieties Of Rice(Oryza Sativa L.) And Genetic Analysis

The utilization of arable saline-alkaline land as arable reserve land is of great significance for promoting food production and sustainable agricultural development.The improved saline-alkaline land still has potential salinity and alkalinity.For this problem,the salt tolerance of crops becomes a crucial target of breeding.Therefore,it is necessary to study the genetic mechanism of salt tolerance which is helpful for the finding of resistant genes.In this study,a salt-tolerant genotype with excellent overall traits(Jiudao-66)was obtained in the screening of saline-alkaline tolerant varieties(with soda saline-alkaline soil).Then a recombinant inbred line population(F7 generation)was constructed with a relative salt-sensitive variety(Kitaake).The saline-alkaline soil leachate was used for stress treatment to analyze the salt-tolerance mechanism and QTL study.At the same time,some innovative researches about notched-belly phenotype of a genotype found in the study were conducted.It provides the basis for rice quality control mechanism and salt-tolerant variety improvement.In general,the study provides a theoretical and practical basis for cultivating and improving salt-tolerant rice varieties.It will accelerate the generalization of these varieties.In the screening of salt-tolerant alkaline varieties(72 genotypes),the mixed soils(normal soil+saline-alkaline soil)with different ratios were used for salt-alkali stress treatment.Then a rice variety Jiudao-66(D68)which is suitable for soda saline-alkaline soil cultivation was obtained.In the mixed soil of 2:1 ratio,the seedling survival rate of Jiudao-66 reached 95%,the membership degree calculated by the salt tolerance index of agronomic traits related to growth was 0.88.The salt tolerance index and seedling survival rate of Jiudao-66 was significantly higher than that of Kitaake.Different salt-tolerance mechanisms in different growth stages of rice have different responses to salt-alkali stress.In this study,the performance of relative salt-sensitive variety(Kitaake)was better than Jiudao-66 in the seed germination stage.Its germination energy,germination rate,relative plumule length,relative radicle length and other related traits are all better than that of Jiudao-66 under stress conditions.Using salt-alkaline soil leachate for stress treatment and QTL analysis,7 QTLs(qGEl,qGE9,qGP1,qGP12,qRPL7,qRRL9,qRRL12)related to salt-tolerance traits during germination stage were mapped,and their phenotypic contribution rates were obtained.They were 14.12%,13.40%,19.35%,8.83%,16.40%,7.32%,and 18.48%,respectively.The research results have practical guiding significance for direct seeding cultivation of saline-alkali land.Seedling stage is a relatively sensitive period for salt-alkali stress of rice,and it is also a very important period of growth and development.At the seedling stage,the leachate of saline-alkaline soil was used for stress treatment.Under the stress of leachate,the content of proline and soluble sugars in the shoots of Jiudao-66 were higher than that of Kitaake,and the total antioxidant capacity was stronger than that of Kitaake.However,the content of malondialdehyde was lower than that of Kitaake.Additionally,the Na+/K+ratios in shoots and roots were not significantly differently between Kitaake and Jiudao-66.The results showed that Jiudao-66,as a salt-tolerant variety,is more tolerant to salt and alkali in a near-natural state due to its stronger tolerance of osmotic stress,and it can accumulate more proline and soluble sugars under stress.At the same time,Jiudao-66 also has a stronger antioxidant capacity.Its ion regulation ability has no obvious advantage.After QTL analysis,13 QTLs(qCHL2,qCHL6,qSFW1,qSFW2,qSDW6,qSDW10,qSDW11,qSPR03,qSPR05,qSSS7,qSTAOC4,qSMDA8,qRMDA8)were mapped which are related to the saline-alkaline tolerance traits at the seedling period.The contribution rates were 18.00%,10.26%,11.79%,10.66%,9.21%,4.56%,17.08%,12.35%,16.65%,11.56%,15.64%,17.36%,17.43%.The rice plants were treated with the leachate from the salt-alkali soil in the natural environment,which was close to the natural state.At the same time,various physiological indexes were determined,and the correlation analysis was accomplished.The results will be meaningful for the rice production.Elite rice cultivars in production tend to show any poor qualities,such as appearance quality(grain shape and chalkiness),so it is necessary to carry out related research on the improvement of the corresponding varieties.For this study,we investigated the incidence of notched-belly grain in a rice cultivar(Jiudao-66)with notched-belly trait under natural conditions(in different years and regions)and artificially controlled conditions.The occurrence of notched-belly grain has a great influence on the appearance quality of rice,which will also affect other qualities,and it is also affected by environmental changes.Cold temperature is one of the causes of notched-belly kernel formation,but it is not the sole factor.Using Kitaake(a cultivar without notched-belly grain)and Jiudao-66 for reciprocal cross and genetic population construction,the percentage of notched-belly grains of Fi hybrids were basically the same,indicating that the genes controlling the notched-belly trait are of nuclear inheritance.In addition,the notched-belly kernel is likely to be formed by the restriction of pericarp during the development of caryopsis.After QTL analysis,3 QTLs(qPNK6?qPNK11-1?qPNKll-2)related to the percentage of notched grains were detected,which the phenotypic contribution rates were 14.47%,9.98%,and 13.24%,respectively.The results laid a foundation for the rice quality improvement.