RESUMEN

BACKGROUND: Harvest index is an important component of grain yield and is typically reduced by reproductive stage drought stress in rice. Multiple drought response mechanisms can affect harvest index including plant water status and the degree of stem carbohydrate mobilization during grain filling. In this study, we aimed to dissect the contributions of plant water status and stem carbohydrate mobilization to harvest index. Pairs of genotypes selected for contrasting harvest index but similar biomass and days to flowering were characterized at ICAR-RCER, Patna, India and at IRRI, Philippines. RESULTS: Multiple traits were related with harvest index across experiments, including mobilization efficiency at both sites as indicated by groupings in principal component analysis, and plant water status as indicated by direct correlations. Biomass-related traits were positively correlated with harvest index at IRRI but biomass was negatively correlated with harvest index at ICER-RCER, Patna. We observed that some pairs of genotypes showed differences in harvest index across environments, whereas other showed differences in harvest index only under drought. Of all time points measured when all genotypes were considered together, the stem carbohydrate levels at maturity were most consistently (negatively) correlated with harvest index under drought, but not under well-watered conditions. However, in the pairs of genotypes grouped as those whose differences in harvest index were stable across environments, improved plant water status resulted in a greater ability to both accumulate and remobilize stored carbohydrate, i.e. starch. CONCLUSION: By distinguishing between genotypes whose harvest index was improved across conditions as opposed to specifically under drought, we can attribute the mechanisms behind the stable high-harvest index genotypes to be more related to stem carbohydrate remobilization than to plant water status. The stable high-harvest index lines in this study (Aus 257 and Wanni Dahanala) may confer mechanisms to improve harvest index that are independent of drought response and therefore may be useful for breeding improved rice varieties.

RESUMEN

Gibberellin (GA)-insensitive dwarfing genes Rht-B1b and Rht-D1b that are responsible for the 'Green Revolution' have been remarkably successful in wheat improvement globally. However, these alleles result in shorter coleoptiles and reduced vigour, and hence poor establishment and growth in some environments. Rht18, on the other hand, is a GA-sensitive, dominant gene with potential to overcome some of the early growth limitations associated with Rht-B1b and Rht-D1b. We assessed progeny from both a biparental and a backcross population that contained tall, single dwarf, and double dwarf lines, to determine whether Rht18 differs from Rht-D1b and hence verify its value in wheat improvement. Progeny with Rht18 had an almost identical height to lines with Rht-D1b, and both were ~26% shorter than the tall lines, with the double dwarf 13% shorter again. However, coleoptile length of Rht18 was 42% longer than that of Rht-D1b. We detected no differences in time to terminal spikelet and anthesis, and few differences in stem or spike growth. Both dwarfing genes diverted more dry matter to the spike than tall lines from prior to heading. No differences were detected between Rht18 and Rht-D1b that could prevent the adoption of Rht18 in wheat breeding to overcome some of the limitations associated with the 'Green Revolution' genes.

Asunto(s)

Giberelinas , Triticum , Pan , Fitomejoramiento , Proteínas de Plantas/genética , Triticum/genética

RESUMEN

KEY MESSAGE: The homologous genes to OsSUT1-5 in wheat were identified and detailed analysed. TaSUT1 was the predominant sucrose transporter group and it illustrated the genotypic variations towards drought during grain filling. Sucrose transporters (SUT) play crucial roles in wheat stem water soluble carbohydrate (WSC) remobilization to grain. To determine the major functional SUT gene groups in shoot parts of wheat during grain development, drought tolerant varieties, Westonia and Kauz, were investigated in field drought experiments. Fourteen homologous genes to OsSUT1-5 were identified on five homeologous groups, namely TaSUT1_4A, TaSUT1_4B, TaSUT1_4D; TaSUT2_5A, TaSUT2_5B, TaSUT2_5D; TaSUT3_1A, TaSUT3_1D; TaSUT4_6A, TaSUT4_6B, TaSUT4_6D; TaSUT5_2A, TaSUT5_2B, and TaSUT5_2D, and their gene structures were analysed. Wheat plants above the ground were harvested from pre-anthesis to grain maturity and the stem, leaf sheath, rachis, lemma and developing grain were used for analysing TaSUT gene expression. Grain weight, thousand grain weight, kernel number per spike, biomass and stem WSC were characterized. The study showed that among the five TaSUT groups, TaSUT1 was the predominant sucrose transporting group in all organs sampled, and the expression was particularly high in the developing grain. In contrast to TaSUT1, the gene expression levels of TaSUT2, TaSUT3 and TaSUT4 were lower, except for TaSUT3 which showed preferential expression in the lemma before anthesis. The TaSUT5 gene group was very weakly expressed in all tissues. The upregulated gene expression of TaSUT1 Westonia type in stem and grain reveal a crucial role in stem WSC remobilization to grain under drought. The high TaSUT1 gene expression and the significant correlations with thousand grain weight (TGW) and kernel number per spike demonstrated the contribution in Kauz's high grain yield in an irrigated environment and high TGW in Westonia under drought stress. Further molecular level identification is required for gene marker development.

Asunto(s)

Grano Comestible/metabolismo , Proteínas de Transporte de Membrana/fisiología , Proteínas de Plantas/fisiología , Triticum/metabolismo , Metabolismo de los Hidratos de Carbono , Deshidratación/metabolismo , Regulación de la Expresión Génica de las Plantas , Genes de Plantas/fisiología , Proteínas de Transporte de Membrana/genética , Filogenia , Proteínas de Plantas/genética , Reacción en Cadena en Tiempo Real de la Polimerasa , Alineación de Secuencia

RESUMEN

Breeding programs with the aim to enhance yield productivity under abiotic stress conditions during the reproductive stage of crops is a top priority in the era of climate change. However, the choice of exploring stay-green or senescence phenotypes, which represent an opposing physiological bearing, are explored in cereal breeding programs for enhanced yield stability to a different extent. Thus, the consideration of stay-green or senescence phenotypes is still an ongoing debate and has not been comprehensively addressed. In this review, we provide arguments for designing a target phenotype to mitigate abiotic stresses during pre- and post-anthesis in cereals with a focus on hormonal balances regulating stay-green phenotype versus remobilization. The two major hypothesis for grain yield improvement are (i) the importance of the stay-green trait to elevate grain number under pre-anthesis and anthesis stress and (ii) fine tuning the regulatory and molecular physiological mechanisms to accelerate nutrient remobilization to optimize grain quality and seed weight under post-anthesis stress. We highlight why a cautious balance in the phenotype design is essential. While stay-green phenotypes promise to be ideal for developing stress-tolerant lines during pre-anthesis and fertilization to enhance grain number and yield per se, fine-tuning efficient remobilizing behavior during seed filling might optimize grain weight, grain quality and nutrient efficiency. The proposed model provides novel and focused directions for cereal stress breeding programs to ensure better seed-set and efficient grain-filling in cereals under terminal drought and heat stress exposure.