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.     

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.     

高产冬小麦深耘断根提高粒重的生理分析

1997～1999采用2个品种,设置4个处理,于花后测定多项生理指标,研究探讨深耘断根提高冬小麦粒重的机理。结果表明：花后深耘断根处理的“源”活力高。深耘断根可推迟小麦旗叶光合速率峰期、延缓叶绿素含量下降速率、延缓功能叶衰老、使根系发育良好、活力提高。深耘断根处理增强籽粒“库”活力。可使籽粒SS（蔗糖合成酶）活性加大、穗部ATP含量提高。深耘断根提高旗叶SPS(磷酸蔗糖合成酶)活性,强化光合产物转化。深耘断根保持了小麦长时期高强度灌浆。结合前人的研究,文章初步提出了冬小麦深耘断根增加粒重的机理模型。     

Genome wide association study of grain yield and yield related traits in spring bread wheat (Triticum aestivum L.) under drought and heat conditions in three different locations

Journal of Crop Science and Biotechnology - Abiotic stress, especially drought and heat, affects cereal yields and wheat production worldwide, more particularly in West and South Asia, North...     

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.     

Differential root responses in two cultivars of winter wheat (Triticum aestivum L.) to elevated ozone concentration under fully open‐air field conditions

The effect of elevated tropospheric ozone concentration [O₃] on root processes in wheat systems of different O₃ sensitivity is not well understood. Two wheat cultivars (cv. Y15 and YN19) with contrasting O₃ tolerance were grown in a fully open‐air O₃ enrichment platform for one season. We found that elevated O₃ (EO₃) (50% above the ambient O₃) significantly decreased the total biomass at all key growth stages and the yield of the O₃‐sensitive cultivar YN19 but did not affect those of the O₃‐tolerant cultivar Y15. EO₃ significantly decreased the root biomass of two wheat cultivars at the jointing and grain‐filling stages. EO₃ significantly decreased the root length, length density, surface area and volume of the two cultivars at the jointing stage but increased those of YN19 at the grain‐filling stage. EO₃ significantly increased the root activities (specific root respiration rates) of Y15 and YN19 at the jointing, heading and grain‐filling stages. EO₃ significantly decreased the contribution of fresh root respiration to soil respiration (CRS) of YN19 at the jointing stage but increased it at the heading stage; however, it did not change the CRS of Y15 at any growth stages. This study indicates that the effects of EO₃ on root morphology and activity varied among wheat cultivars, and suggest that we can breed O₃‐tolerant cultivars to maintain crop yield under higher [O₃] scenarios.     

The stage sensitivity of short‐term heat stress to lodging‐resistant traits and yield determination in canola (Brassica napus L.)

With the expected increase of abiotic stress under global climate change, significant research has been devoted to how abiotic stress will affect crop production. To date, there has been little research on the stage sensitivity of short‐term heat stress to crop lodging and yield determination in canola. This research was conducted in a controlled growth facility and aimed to examine root morphology, pod fertility, seed yield and crop lodging of two contrasting canola genotypes subjected to a short‐term heat stress (27.0/24.3°C, light/dark), imposed respectively at three growth stages, rosette vegetative stage (RVHT), early flowering stage (EFHT) and late flowering stage (LFHT), in comparison with non‐stressed control (CK) (23/17°C). The results demonstrate that heat stress imposed at RVHT and LFHT was less detrimental to seed yield and lodging resistance. However, EFHT showed significant adverse effects on both, which was further confirmed by redundancy analysis (RDA) and structural equation modelling (SEM). Compared with the CK, EFHT resulted in a yield loss of 43%, which was mainly due to poor pod fertility, less number of filled pods (?28%), decreased pollen viability (?38%) and a lower success ratio of filled pods (?29%). The taproot was found to be relatively tolerant to heat stress, but lateral roots were sensitive to heat stress at EFHT and LFHT. Root capacitance could be used as a non‐destructive method for evaluating lateral root morphology. Compared with the CK, EFHT displayed a high risk of stem lodging, as indicated by a 27% lower safety factor. This was mainly attributed to the reduced stem bending strength that was caused by the deterioration of stem mechanical properties under EFHT, as illustrated by SEM. Root lodging resistance was not altered by any stages of short‐term heat stress, as the taproot remained stable.