Genetic dissection of grain yield traits in a large collection of spring wheat (Triticum aestivum L.) germplasm

Journal of Crop Science and Biotechnology - Understanding genetic architecture of a crop germplasm is necessary for designing a successful breeding program. Herein, we evaluated a large collection...     

普通小麦氮素利用效率相关性状全基因组关联分析

氮元素在粮食作物生长和发育过程起着不可替代的作用。发掘氮素利用效率相关基因对于提升小麦产量、减少环境污染具有重要意义。植株根系构型(rootsystemarchitecture,RSA)代表着根系的结构及空间造型,显著受氮素水平影响。本研究在正常供氮和缺氮两种氮素水平下,对160份来自黄淮冬麦区和北部冬麦区普通小麦品系的根系构型相关性状(总根长、总根表面积、总根体积、平均根直径和根尖数)进行统计,并结合小麦660KSNP(single nucleotidepolymorphism)芯片基因分型数据对根系相关性状的相对值进行全基因组关联分析,以期发掘氮素利用效率相关位点。本研究检测到34个与氮素利用效率显著关联的SNP位点,可解释6.9%～15.4%的表型变异。关联位点在所有染色体均有分布,主要集中于1A、2B、3B、5B、6A、6B和7A染色体。11个位点与已报道位点重叠或接近,其他23个位点可能为新的位点。另外,在3B染色体上发现一个编码E3泛素连接酶的候选基因。     

Cytoplasmic effects on quality traits of bread wheat (Triticum aestivum L.)

The inheritances of thousand kernel weight (TKW), protein percentage, protein quality and grain hardness were studied through an 11 x 11 complete diallel set of bread wheat genotypes consisting of four alloplasmic lines of Selkirk, two alloplasmic lines of Siete Cerros 66, and five commercial cultivars. Genetic components accounted for 93%, 90%, 78%, and 92% of total variation for TKW, protein percentage, protein quality, and grain hardness, respectively. General combining ability (GCA) effects were dominant for TKW (48% GCA, 38% SCA [specific combining ability], and 7% reciprocal effects [RE]), protein percentage (70% GCA, 10% SCA, and 10% RE), and grain hardness (59% GCA, 29% SCA, and 4% RE). However, SCA effects dominated for protein quality (30% GCA, 43% SCA, and 5% RE). Broad- and narrow-sense heritabilities were estimated at 0.95 and 0.65 for TKW, 0.94 and 0.82 for protein percentage, 0.83 and 0.47 for protein quality, and 0.95 and 0.74 for grain hardness. Reciprocal effects were highly significant for all quality traits, but less effective than additive and non-additive gene effects. Aegilops cylindrica, Ae. ventricosa, and Triticum turgidum cytoplasms showed positive effects on TKW in some crosses. Ae. cylindrica, Ae. variabilis, and Ae. uniaristata cytoplasms seemed to have potential for improving protein percentage. T. aestivum cytoplasms were superior to alien cytoplasms for protein quality. Bolal 2973, Kiraç 66 and Bezostaja 1 cytoplasms increased protein quality in some crosses. Ae. cylindrica, Ae. variabilis, Ae. ventricosa and Ae. uniaristata cytoplasms had significant effects on grain hardness. The cytoplasmic variation in B type T. aestivum cytoplasm was found to be significant for all traits.     

Vernalization gene combination to maximize grain yield in bread wheat (Triticum aestivum L.) in diverse environments

The major vernalisation genes of VRN1 are well understood at the molecular level. However, their quantitative contributions to flowering time and grain yield related traits are not clear. In this study, we used a double haploid population (225 lines) of Westonia × Kauz in which the Vrn-A1a (Westonia), Vrn-B1a (Westonia) and Vrn-D1a (Kauz) were segregating, and a high resolution genetic map of 1,159 loci, to determine the quantitative contributions of Vrn-A1a, Vrn-B1a and Vrn-D1a for the days to anthesis and grain yield related traits in diverse environments. The major quantitative trait loci (QTL) of spikelet number per spike and days to anthesis were contributed by the winter alleles of VRN1. The QTL of the time of grain filling were contributed by the spring alleles of VRN1. The wild genotype (vrn-A1vrn-B1vrn-D1) showed the latest flowering, the highest spikelet number per spike, lowest peduncle proportion and thousand grain weight in three environmental analyses, and the largest spikelet number per spike, which resulted in high kernel number per spike (KN) and grain weight (GW) in well-watered environments. One QTL of KN was located on 5B, contributed by winter allele of vrn-B1 in three environmental analyses, and one GW QTL was detected on 5A, contributed by the spring allele of Vrn-A1a in a drought environment. The results indicated that the genotype Vrn-A1avrn-B1Vrn-D1a would shorten the time to anthesis and give high GW and KN in drought environments. The early anthesis associated phenotype, peduncle proportion would provide an indicator in breeding programs.     

Mapping quantitative trait loci associated with grain filling duration and grain number under terminal heat stress in bread wheat (Triticum aestivum L.)

Terminal heat stress has the potential negative impact on wheat production across the world, especially in South Asia. Under the threat of terminal heat stress, wheat genotypes with stay green trait would suffer from high temperature stress during their long grain filling duration (GFD). The genotypes with short GFD would be advantageous. To identify quantitative trait loci (QTL) for heat tolerance, a RIL population of K 7903 (heat tolerant) and RAJ 4014 (heat sensitive) wheat genotypes was investigated under timely and late‐sown conditions. Heat susceptibility index of GFD, yield components and traits under late‐sown condition were used as phenotypic data for QTL identification. Stable QTLs associated with these traits were identified on chromosomes 1B, 2B, 3B, 5A and 6B. The LOD value ranged from 2.9 to 5.0 and the corresponding phenotyping variation explained ranged from 12.0–22%. QTL for heat susceptibility index for the grain filling duration were colocalized with QTL for productive tillers under late sown and GFD under late‐sown condition on chromosomes 1B and 5A, respectively. These genomic regions could be exploited for molecular wheat breeding programmes targeting heat tolerance.     

Expression analysis of the genes involved in osmotic adjustment in bread wheat (Triticum aestivum L.) cultivars under terminal drought stress conditions

Osmotic adjustment is the main component for physiological machinery of wheat drought tolerance. Some of parameters implicated in osmotic adjustment in 15 bread wheat cultivars were evaluated at soil water deficits (50% FC) and FC as the control in the greenhouse. For the physiological traits, analysis of variance showed that there are highly significant differences between treatments, i.e. water stress levels and wheat cultivars. Shahpasand and Marvdasht as sensitive wheat cultivars had significantly lower osmotic adjustment, relative water content, K+ content, soluble sugar, proline, and glycine betaine levels than the rest of the cultivars. The results of cluster analysis revealed that all cultivars were grouped into three distinct clusters. Dez, Kavir, Pishtaz, and Maron cultivars which have the highest osmoregulation activity were in cluster I, whereas clusters II (Pishgam, Aflak, Hirmand, Zagros, and Vee/Nac) and III (Ws-89-2, Sardari, Azar2, Shapasand, and Marvdasht) had intermediate activity and the lowest capacities for osmoregulation, respectively. In addition, in wheat flag leaf during the reproductive stage under drought conditions, the changes in gene expression of two key genes namely P5CS (D-Pyrroline-5-carboxylate synthetase) and BADH (Betaine Aldehyde Dehydrogenase) in two selected cultivars including Dez and Marvdasht revealed that water stress can increase the expression level of the genes P5CS and BADH in the resistant cultivar, Dez, compared with Marvdasht, the sensitive one. In general, it seemed that application of the all cultivars in cluster I would enable breeders to acquire more reliable achievements under drought conditions.     

Association of staygreen trait with canopy temperature depression and yield traits under terminal heat stress in wheat (Triticum aestivum L.)

The presence or absence of the staygreen trait was screened for 3 consecutive years in 963 wheat lines from various sources, including Indian and CIMMYT germplasm. Staygreen was assessed at the late dough stage by visual scoring (0–9 scale) and the leaf area under greenness (LAUG) measurement. Around 5.5 % of the lines were staygreen, 10.5 % were moderately staygreen, and the remaining lines showed little or no expression of the trait. One hundred lines showing diversity for the staygreen trait were sown under three different sowing dates (timely, late and very late) for 3 consecutive years in three replications to determine the association of staygreen with heat tolerance. There was a decline in yield, biomass, grain filling duration (GFD) and 1,000 grain weight (TGW) under late and very late sowing conditions owing to terminal stress at anthesis and later stages. However, the decline was relatively less in staygreen genotypes compared to the non-staygreen (NSG) ones. The correlation study showed that LAUG and canopy temperature depression (CTD) were strongly correlated. LAUG and CTD were also significantly associated with grain yield, GFD and biomass. To further confirm the association of the staygreen trait with terminal heat stress, individual F₂-derived F₇ progenies from the cross of the ‘staygreen’ lines with NSG were evaluated for yield and yield traits at the three sowing dates. In each cross, the staygreen progenies showed a significantly smaller decline in yield and TGW under heat stress than the NSG progenies. These results appear to suggest an association between the staygreen trait and terminal heat stress and, thereby, that the staygreen trait could be used as a morphological marker in wheat to screen for heat tolerance.     

Combining ability and gene action controlling yield and yield components in bread wheat (Triticum aestivum L.) under drought‐stressed and nonstressed conditions

This study determined the combining ability and gene action controlling yield and yield‐related traits in wheat under drought‐stressed and nonstressed conditions. Twelve parents possessing Rht‐B1b and Rht‐D1a genes and their 66 half‐diallel crosses were evaluated under field and glasshouse conditions. Plant height (PH), productive tiller number (TN), kernels per spike (KPS), thousand seed weight (TSW) and grain yield (GY) were recorded. Analysis of variance, heritability, correlation and combining ability analyses were performed. Heritability estimates ranged from 53.00% (TN) to 63.07% (KPS). Yield showed positive correlations with all other traits under all test conditions. Significant GCA effects were observed for all traits recorded across test conditions, except for yield in the glasshouse. All Baker's ratios were less than a unit, indicating predominance of nonadditive gene action. Consistently high positive GCA effects were observed on LM02 for GY; LM02 and LM23 for KPS; and LM04 and LM09 for TSW, while LM17 and LM21 had negative effects for PH. Good general and specific combiners will be used for further breeding and selection.     

Substitution analysis of drought tolerance in wheat (Triticum aestivum L.)

Chromosome substitution lines of the wheat variety ‘Cappelle Desprez’ into ‘Chinese Spring’ were tested for drought tolerance in growth chambers in the Martonvásár phytotron. Three different moisture regimes were created: E1, fully irrigated control; E2, mid-season water stress (preanthesis); and E3, terminal water-stress during grain filling. Data were analysed to estimate the chromosomal location of the genes controlling relative water-content (RWC), relative water-loss (RWL), drought-susceptibility index (DSI) and phenotypic stability in each substitution line. Simultaneous consideration indicated that most of the genes controlling these characters are located on chromosomes 1A, 5A, 7A,4B, 5B, 1D, 3D and 5D.     

Effects of dwarfing genes on yield and yield components under irrigated and rainfed conditions in wheat (Triticum aestivum L.)

Summary Near-isogenic tall (no dwarfing gene), semidwarf (Rht1 or Rht2) and dwarf (Rht1 + Rht2 or Rht3) spring wheat lines were evaluated for yield and yield components under irrigated and rainfed conditions. Under irrigated conditions, the dwarf and the semidwarf lines exhibited a significant yield advantage over the tall lines. Under rainfed conditions, the semidwarf lines outyielded the tall as well as the dwarf lines. Percent yield reduction in response to drought stress was highest with the dwarfs and lowest with the tall lines. Dry matter production of the tall lines and that of the semidwarf lines did not differ significantly and both produced significantly more dry matter than the dwarf lines under irrigated as well as rainfed conditions. Plant height and kernel weight decreased with increasing degree of dwarfness while number of kernels per spikelet, harvest index and days to heading increased under both moisture regimes. The dwarfing genes did not have any significant influence on number of tillers/m² and spikelets per spike in either moisture regime.     

Detection of QTLs for traits associated with pre-harvest sprouting resistance in bread wheat (Triticum aestivum L.)

Pre-harvest sprouting (PHS) is one of the serious problems for wheat production, especially in rainy regions. Although seed dormancy is the most critical trait for PHS resistance, the control of heading time should also be considered to prevent seed maturation during unfavorable conditions. In addition, awning is known to enhance water absorption by the spike, causing PHS. In this study, we conducted QTL analysis for three PHS resistant related traits, seed dormancy, heading time and awn length, by using recombinant inbred lines from ‘Zenkouji-komugi’ (high PHS resistance) × ‘Chinese Spring’ (weak PHS resistance). QTLs for seed dormancy were detected on chromosomes 1B (QDor-1B) and 4A (QDor-4A), in addition to a QTL on chromosome 3A, which was recently cloned as TaMFT-3A. In addition, the accumulation of the QTLs and their epistatic interactions contributed significantly to a higher level of dormancy. QDor-4A is co-located with the Hooded locus for awn development. Furthermore, an effective QTL, which confers early heading by the Zenkouji-komugi allele, was detected on the short arm of chromosome 7B, where the Vrn-B3 locus is located. Understanding the genetic architecture of traits associated with PHS resistance will facilitate the marker assisted selection to breed new varieties with higher PHS resistance.     

Genetic analysis of adult plant leaf rust resistance in three bread wheat (Triticum aestivum L.) cultivars

Genetic basis of adult plant leaf rust resistance in three released Indian wheat cultivars viz. DWR195, RAJ3765 and HP1731 was investigated through detailed inheritance study under controlled polythene house condition at Flowerdale, India. The F₂, F_3, F₄ and F₅ generations were analyzed with the most frequent and virulent Indian leaf rust pathotype 121R63-1. Two complementary recessive genes imparted resistance in DWR195, two complementary dominant genes governed the resistance of RAJ3765 whereas two independent dominant genes were involved in the resistance of HP1731. The genes responsible for adult plant resistance in the three cultivars were not allelic. The two complementary genes of DWR195 and two independent dominant genes of HP1731 have been isolated as single gene lines. Utilization of resistance from HP1731, which carries two independent dominant genes, will be easy as compared to DWR195 and RAJ3765.     

Inheritance of net photosynthesis and transpiration efficiency in spring wheat, Triticum aestivum L., under drought

The inheritance of net photosynthesis and transpiration effciency in spring wheat under drought were studied in two years in order to determine their heritability. The parents, F₁ and segregating generationsf (F₁, BC₁, BC₁) of four crosses between each of two drought-resistant and two drought-susceptible genotypes were evaluated under drought in pots under glasshouse conditions. Measurements of gas exchange were made using a portable gas-analysis system. Generation means and variance component analyses of the data suggested that these traits are simply inherited and controlled mainly by additive genetic variation. Narrow-sense heritability estimates varied between crosses from 61% to 84% for net photosynthesis and from 88% to 89% for transpiration effciency.     

Variation in pigment content of flour color in bread wheat (Triticum aestivum L.)

Summary Variation in pigment content of the flour of bread wheats (Triticum aestivum L.) was studied in the progenies of F₁ and F₂ of three crosses and their reciprocals. Reciprocal differences in pigment content were observed in the F₁ and F₂ means. Low pigment content was found to be partially dominant or over dominant in the crosses studied. There was evidence of substantial mid-parent F₁ heterosis in all crosses and betterparent F₁ heterosis in three crosses. In the F₂, heritability estimates were moderate to high. The F₂ frequency distributions were not normal. Estimation of effective factor pairs indicated the presence of one or two major gene pairs involved in the expression of pigment content in the flour. Action of modifiers was also assumed in one cross and its reciprocal. A factorial approach to metrical character suggested that the F₂ segregation ratios of low pigment content to high pigment content were 3:1, 15:1, 13:3 and 9:7 for the different crosses. Utilization of the findings in a wheat breeding program is briefly discussed.     

Stability analysis over seasons and locations of multilines of wheat (Triticum aestivum L.)

Summary Three multilines each of Kalyansona and PV 18 varieties of wheat were compared for their stability of yield and agronomic characters and disease resistance against the respective recurrent parents. The experiments were conducted for four years at nine locations.The multilines had more tillers and bolder seeds than the recurrent parents. There were, however, no differences for plant height, ear length and number of spikelets per spike.The genotypes x years x locations interaction was much more important than genotypes x years or genotypes x locations interaction as well as the main effects for genotypes. It is suggested that the number of test locations should be increased while decreasing the number of years.The stability parameters indicated that the multilines had a higher mean yield in the case of Kalyansona multilines whereas the yield of multilines of PV 18 was not significantly inferior to that of the recurrent parent. The regression coefficients were very close to unity except for KSML 3 (b=1.132). The deviations from regression were much larger for the multilines than for the recurrent parents.For rust resistance the multilines were superior over the varieties Kalyansona and PV 18.This is publication No. 9 of the series Studies on multilines in wheat (Triticum aestivum L.)     

Response to early generation selection for grain yield and harvest index in bread wheat (T, aestivum L.)

The availability of a reliable selection criterion for the identification of the most productive genotypes in early generations represents a crucial point in many breeding programs. The findings reported in the literature concerning the effectiveness of early generation testing for grain yield (GY) or harvest index (HI) are contradictory. In this work, we measured the response to selection for GY and HI applied in different generations, from F₂ to F₆ in nine segregating populations previously screened in F₂ by means of visual selection. Genetic variability for HI and GY was found in most of the segregating populations. However, GY of spaced plants in F₆ and F₃ generations was weakly correlated with yield of F₄ and successive generations grown at normal seed density. HI was of limited value as an indicator of yield potential.