Studies on genotypic variability and inheritance of waterlogging tolerance in wheat

[摘要] English: Analysis of genetic relationships in crop species can provide a relative measure ofgenetic diversity, an index of parental selection and structure for stratified sampling ofpopulations. Seed storage proteins of 38 Ethiopian-grown and four advanced CIMMYTlines were fractionated by one-step sodium dodecyl sulfate-polyacrylamide gelelectrophoresis (SDS-PAGE) to assess the composition of the three major endospermproteins, determine the level of genetic diversity and search for the number of clustersamong the genotypes of hexaploid wheat which is believed to be a relatively recentintroduction to the Ethiopian highlands. The results indicated that there was a widerange of allelic variation in the composition of gliadins, low molecular weight (LMWGS)and high molecular weight (HMW-GS) glutenin subunits among the differentgenotypes studied. A total of 82 polymorphic bands, i.e., 32 gliadins, 35 LMW-GS and15 HMW-GS bands, were detected among the 42 genotypes. The mean protein-basedgenetic distance estimate was 0.609 unit with values ranging from 0.376 to 0.744 units.Over 80% of pairwise comparisons had genetic distance values between 0.440 and0.700 units. Cluster analysis also resulted in five genetically distinct groups ofgenotypes.Soil waterlogging is a serious environmental stress affecting wheat production in thehigh rainfall or irrigated areas with heavy clay Vertisols. Sixteen bread wheat genotypeswere evaluated for their tolerance to prolonged transient and continuous waterloggingtreatments. The results indicated that increased severity of soil waterlogging stresssignificantly reduced grain yields and growth of wheat; continuous waterlogging, inparticular, resulted in greater damage to the plants in terms of most of the characteristicsstudied. The results also demonstrated that there were marked genotypic differencesamong the wheat genotypes studied for waterlogging tolerance. Ducula xl, PRL/Sara,HAR 604 and Vee/Myna were relatively tolerant whereas Et-13 and K 6290-Bulk weremost sensitive to waterlogging stress. Under continuous waterlogging, grain yield wascorrelated positively with grains per spike and spikelet, kernel mass, biomass yield,number of green leaves on the main stem, the stress tolerance index, and negatively withpercentage leaf chlorosis, area under chlorosis progress curve and the stress toleranceindex. Percentage leaf chlorosis, biomass yield, number of grains per spike and spikelet,and kernel mass accounted for over 88% of the total variation in the grain yield undercontinuous waterlogging. Heritability values of these characteristics and indices werealso fairly large, indicating a promising gain from selection based on thesecharacteristics.Waterlogging of soils restricts crop performance by altering the soil mineral nutrient.availability and uptake by roots. Two experiments were conducted to determine theeffects of soil waterlogging on nutrient availability, and on the concentration and uptakeof nutrients by wheat genotypes that differ in tolerance, and to assess the response ofwaterlogged wheat seedlings to foliar applications of selected nutrients. Root zoneoxygenation was significantly depressed by the waterlogging treatments as indicated bysignificantly reduced soil redox potentials. All the IN Nlia-acetate (pH 7.0) extractablemineral nutrient concentrations in the soil increased as waterlogging severity increased.A significant differential response of wheat genotypes to the waterlogging treatmentswas detected for several mineral nutrient concentration and uptake parameters.Compared to the tolerant genotypes, the sensitive genotypes appeared to accumulatemore Fe, Mn, and Na although the concentrations were far below the level of toxicityreported for these nutrients, and less Cu, Zn, K, Pand N with concentrations lower thanthe critical values previously reported for wheat. The results from the foliarapplication study indicated that waterlogging tolerance of wheat could be improvedwith the foliar application of Zn, Cu and P.A study was undertaken to assess the combining ability effects, variance components,heterotic responses, heritability and correlations of waterlogging tolerance in a diallelcross involving five diverse bread wheat genotypes with contrasting tolerance responseto waterlogging stress. The results showed that genotypic variability accounted for mostof the variation among genotypes studied. Highly significant general combining ability(GCA) and specific combining ability (SCA) were observed for most of thecharacteristics studied, indicating that both additive and dominance gene effects wereimportant in the inheritance of the waterlogging tolerance. GCA effects, however, wererelatively more prevalent than SCA effects on most of the characteristics studied. Thetolerant genotypes PRL/Sara and Ducula were the best combiners for waterloggingstress tolerance and for most other agronomic characteristics studied. Relatively highestimates of heritability and predictability ratios were also observed for mostcharacteristics relevant to waterlogging tolerance, confirming the importance of bothadditive and non-additive gene effects in controlling the waterlogging tolerance inwheat genotypes studied. The degree of dominance for waterlegging tolerancecharacteristics was estimated to be in the partial and complete dominance range. Underwaterlogging conditions, grain yield correlated with genotypically and phenotypicallypositively with all its components, biomass yields, plant height, days to heading,number of green leaves on the main stem and stress tolerance index, and negatively withpercentage leaf chlorosis, area under leaf chlorosis progress curve and stresssusceptibility index. Substantial mid- and high- parent heterotic responses wereobserved for most characteristics in some crosses.

[发布机构] University of the Free State