Identification of stable quantitative trait loci underlying waterlogging tolerance post-anthesis in common wheat(Triticum aestivum)

Waterlogging is a growing threat to wheat production in high-rainfall areas.In this study,a doubled haploid(DH) population developed from a cross between Yangmai 16(waterlogging-tolerant) and Zhongmai895(waterlogging-sensitive) was used to map quantitative trait loci(QTL) for waterlogging tolerance using a high-density 660K single-nucleotide polymorphism(SNP) array.Two experimental designs,waterlogging concrete tank(CT) and waterlogging plastic tank(PT),were used to simulate waterlogging during anthesis in five environments across three growing seasons.Waterlogging significantly decreased thousand-kernel weight(TKW) relative to non-waterlogged controls,although the degree varied across lines.Three QTL for waterlogging tolerance were identified on chromosomes 4AL,5AS,and 7DL in at least two environments.All favorable alleles were contributed by the waterlogging-tolerant parent Yangmai16.QWTC.caas-4AL exhibited pleiotropic effects on both enhancing waterlogging tolerance and decreasing plant height.Six high-confidence genes were annotated within the QTL interval.The combined effects of QWTC.caas-4AL and QWTC.caas-5AS greatly improved waterlogging tolerance,while the combined effects of all three identified QTL(QWTC.caas-4AL,QWTC.caas-5AS,and QWTC.caas-7DL) exhibited the most significant effect on waterlogging tolerance.Breeder-friendly kompetitive allele-specific PCR(KASP) markers(K_AX_111523809,K_AX_108971224,and K_AX_110553316) flanking the interval of QWTC.caas-4AL,QWTC.caas-5AS,and QWTC.caas-7DL were produced.These markers were tested in a collection of 240 wheat accessions,and three superior polymorphisms of the markers distributed over 67elite cultivars in the test population,from the Chinese provinces of Jiangsu,Anhui,and Hubei.The three KASP markers could be used for marker-assisted selection(MAS) to improve waterlogging tolerance in wheat.

QTLs for Waterlogging Tolerance at Germination and Seedling Stages in Population of Recombinant Inbred Lines Derived from a Cross Between Synthetic and Cultivated Wheat Genotypes

Waterlogging is a widespread limiting factor for wheat production throughout the world. To identify quantitative trait loci （QTLs） associated with waterlogging tolerance at early stages of growth, survival rate （SR）, germination rate index （GRI）, leaf chlorophyll content index （CCI）, root length index （RLI）, plant height index （PHI）, root dry weight index （RDWI）, shoot dry weight index （SDWI）, and total dry weight index （DWI） were assessed using the International Triticeae Mapping Initiative （ITMI） population W7984/Opata85. Significant and positive correlations were detected for all traits in this population except RLI. A total of 32 QTLs were associated with waterlogging tolerance on all chromosomes except 3A, 3D, 4B, 5A, 5D, 6A, and 6D. Some of the QTLs explained large proportions of the phenotypic variance. One of these is the QTL for GRI on 7A, which explained 23.92% of the phenotypic variation. Of them, 22 alleles from the synthetic hexaploid wheat W7984 contributed positively. These results suggested that synthetic hexaploid wheat W7984 is an important genetic resource for waterlogging tolerance in wheat. These alleles conferring waterlogging tolerance at early stages of growth in wheat could be utilized in wheat breeding for improving waterlogging tolerance.

Screening Methods for Waterlogging Tolerance at Maize (Zea mays L.) Seedling Stage

Waterlogging strongly affects agronomic performance of maize （Zea mays L.）. In order to investigate the suitable selection criteria of waterflooding tolerant genotypes, and identify the most susceptible stage and the best continuous treatment time to waterlogging, 20 common maize inbred lines were subjected to successive artificial waterflooding at seedling stage, and waterlogging tolerance coefficient （WTC） was used to screen waterflooding tolerant genotypes. In addition, peroxidase （POD） activities and malondialdehyde （MDA） contents were measured for 6 of 20 lines. The results showed that the second leaf stage （V2） was the most susceptible stage, and 6 d after waterflooding was the best continuous treatment time. Dry weight （DW） of both shoots and roots of all lines were significantly reduced at 6 d time-point of waterlogging, compared to control. POD activities and MDA contents were negatively and significantly correlated, and the correlation coefficient was -0.9686 （P 〈 0.0001）. According to the results, WTC of shoot DW can be used for practical screening as a suitable index, which is significantly different from control and waterlogged plants happened 6 d earlier. Furthermore, leaf chlorosis, MDA content and POD activities could also be used as reference index for material screening. The implications of the results for waterlogging-tolerant material screening and waterlogging-tolerant breeding have been discussed in maize.

Unraveling waterlogging tolerance-related traits with QTL analysis in reciprocal intervarietal introgression lines using genotyping by sequencing in rapeseed(Brassica napus L.)

Soil waterlogging is a major environmental stress that suppresses the growth and productivity of rapeseed(Brassica napus L.).Natural genetic variations in waterlogging tolerance(WT)were observed but no QTL mapping has been done for WT related traits in rapeseed.In this study,QTL associated with three WT related traits including relative root length(RRL),relative hypocotyl length(RHL)and relative fresh weight(RFW)were dissected using a set of reciprocal introgression lines(ILs)derived from the cross GH01×ZS9,which showed significant difference in WT.Genotyping-by-sequencing(GBS)of the populations were performed,totally 1468 and 1450 binned SNPs were identified for GIL(GH01 as the recurrent parent)and ZIL(ZS9 as the recurrent parent)population,respectively.A total of 66 distinct QTLs for WT at the seedling establishment stage including 31 for RRL,17 for RHL and 18 for RFW were detected.Among the 66 QTLs,20(29.4%)QTLs were detected in both genetic backgrounds and then they were integrated into six QTL clusters,which can be targeted in rapeseed breeding for improvement of WT through marker-assisted selection(MAS).Based on the physical positions of SNPs and the functional annotation of the Arabidopsis thaliana genome,56 genes within the six QTL cluster regions were selected as preliminary candidate genes,then the resequencing and transcriptome information about parents were applied to narrow the extent of candidate genes.Twelve genes were determined as candidates for the six QTL clusters,some of them involved in RNA/protein degradation,most of them involved in oxidation-reduction process.These findings provided genetic resources,candidate genes to address the urgent demand of improving WT in rapeseed breeding.

Changes of Physiological Characters of Wheat After Water-logging at Booting and Relations Between Physiological Characters and Waterlogging Tolerance

Effects of waterlogging on some physiological characters and relationship between waterlogging tolerance and some characters of their own were studied by using 12 varieties of wheat. Results showed waterlogging made the content of malondialdehyde in flag leaf increase, made the root vigor, the content of chlorophyll, the net photosynthesis rate, the nitrate reductase activity, the relative water content of flag leaf decrease, the content of organic matter change obviously, and then the yield per plant declined. The correlations

Preliminary Study on the Waterlogging Tolerance of 116 Corn Materials

Maize is one of the most important food crops in the world.With the global warming,waterlogging stress has become an important abiotic stress factor that affects crop growth,including maize.Waterlogging seriously affects 10%of the arable land and can lead to a 15%-80%reduction in crop yield[1].In this study,115 inbred line materials commonly used in spring maize planting areas in the Jianghan Plain,Hubei,and maize inbred line B73 with complete genome information,were collected and stressed by waterlogging for two weeks in the seven-leaf and one-heart stage,and the survival rate was statistically compared and analyzed,aiming to screen germplasms with strong waterlogging tolerance for the genetic improvement of waterlogging tolerance of Hubei maize lines.

Combining Ability and Genetic Effects of Germination Traits of Brassica napus L.Under Waterlogging Stress Condition

Cross combinations from six rapeseed cultivars and lines were evaluated under waterlogging stress condition in order to understand the genetic mechanism of waterlogging tolerance of Brassica napus L.and provide reasonable improvement programs.There were six germination traits investigated on combining ability and heritability using complete diallel crossing method designed for 30 combinations from those six cultivars and lines.The traits included relative root length,stem length,fresh weight per plant,survival rate,electrical conductivity,and vigor index.After flooding treatment,the six traits of parents and F1 were analyzed.The general combining ability（GCA） and special combining ability（SCA） of germination traits were analyzed using Griffing I method.Among 30 cross combinations,the GCA was significantly different among six waterlogging resistance traits.The SCA of these traits was significantly different except the SCA of electrical conductivity.As a representative trait of waterlogging tolerance in rapeseed,relative vigor index had the highest narrow heritability and relatively low broad heritability.The cultivars Zhongshuang 9 and P79 had higher tolerance potential to waterlogging stress.It can be concluded that combining ability and genetic effects of relative vigor index during germination stage could be used to identify the waterlogging tolerance of rapeseed in breeding program.