Effects of soil water deficit at different growth stages on rice growth and yield under upland conditions. 2. Phenology, biomass production and yield
ABSTRACT Phenological development, shoot dry matter production, grain yield and yield components of rice were examined in relation to drought occurring at various stages of growth. Rice was sown three or four times at three-week intervals in the field in each of two years, and performance in three stress trials was compared with that in corresponding irrigation trials, with the aim of quantifying the response of the crop to water stress of 23–34 days' duration developing at different growth stages. When drought occurred during vegetative stages, it had only a small effect on subsequent development and grain yield. The reduction in yield of up to 30% was due to reduced panicle number per unit area in one trial, and reduced number of spikelets per panicle in another. The effect of water stress on yield was most severe when drought occurred during panicle development. Anthesis was delayed, the number of spikelets per panicle was reduced to 60% of the irrigated control and the percentage of filled grains decreased in one crop to zero. This decrease in grain yield to less than 20% of the control was associated with low dry matter production during the drought period as well as during the recovery period following the drought. When drought occurred during grain filling, the percentage of filled grains decreased to 40% and individual grain mass decreased by 20%. The effect of stress was also related to its severity during grain filling. Stress at this stage hastened maturity. The results suggest that variation in yield components due to water availability is related to the variation in dry matter production at particular growth stages. Results of a supplementary shading experiment show that the relationship between spikelet number per panicle or single grain mass and crop growth rate was the same, whether growth rate was varied by availability of soil water or solar radiation. Filled-grain percentage, however, was more sensitive to drought stress than shading when comparison was made at a similar crop growth rate.
- SourceAvailable from: Rakesh Kumar Singh[Show abstract] [Hide abstract]
ABSTRACT: Rice does not behave similarly under salt-stress across all the plant growth stages but respond differentially at different stages of development. Seedling and reproductive stages are the most sensitive growth stages however, association between tolerances at the two stages is very weak, suggesting that they are regulated by different processes and set of genes/QTLs. There are numerous reports for the seedling stage salinity tolerance in rice, obviously due to ease in phenotyping which is very well standardized. But hardly there are studies on reproductive stage salinity tolerance mainly due to lack of reliable reproductive stage-specific phenotyping techniques and incomplete knowledge of the stage specific mechanisms of salinity tolerance. There are two major challenges for salinity screening exclusively for reproductive stage. First, how to stress the plants at the reproductive stage without stressing seedling or late vegetative stage. Second, how to impose the stress different genotypes or mapping population at equivalent growth stages of development (for 10-20 days spanning the period of anthesis) because of the variability in growth rate of progression through developmental stages. To standardize this, we devised a methodology that fasten the salt translocation to the reproductive organs like flag leaf (biggest source for the sink) and panicle as quickly as possible just at the initiation of booting when the genotypes are at the same stage of tissue/organ development rather than age of plant. Extra leaves were clipped leaving only minimum number of leaves needed by the rice plant that will not significantly affect grain yield and yield components. Salt stress equivalent to EC 10 dSm-1 was imposed to rice plants with trimmed leaves starting from boot leaf emergence up to 20 days in a pot experiment under controlled conditions. The stage-specific effect of salt stress was verified by observing salt-sensitive and salt-tolerant genotypes. Leaf cutting before the booting stage efficiently directed the salt concentration to the reproductive stage and helped in discriminating the tolerant genotypes from the sensitive ones as evidenced by the low pollen viability and higher accumulation of toxic ions in the flag leaf of the sensitive genotype (IR64). The opposite was found true for the tolerant genotype (IR4630-22-2-5-1-3). Details will be discussed during presentation.European Field Phenotyping Workshop University of Copenhagen, Denmark, Denmark; 09/2014
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ABSTRACT: OsiSAP1, an A20/AN1 zinc-finger protein, confers water-deficit stress tolerance at different stages of growth by affecting expression of several endogenous genes in transgenic rice. Transgenic lines have been generated from rice constitutively expressing OsiSAP1, an A20/AN1 zinc-finger containing stress-associated protein gene from rice, driven by maize UBIQUITIN gene promoter and evaluated for water-deficit stress tolerance at different stages of growth. Their seeds show early germination and seedlings grow better under water-deficit stress compared to non-transgenic (NT) rice. Leaves from transgenic seedlings showed lesser membrane damage and lipid peroxidation under water-deficit stress. Relatively lower rate of leaf water loss has been observed in detached intact leaves from transgenic plants during late vegetative stage. Delayed leaf rolling and higher relative water content were also observed in transgenic plants under progressive water-deficit stress during reproductive developmental stage. Although reduction in grain yield is observed under unstressed condition, the relative water-deficit stress-induced yield losses are lower in transgenic rice vis-à-vis NT plants thereby resulting in yield loss protection. Transcriptome analysis suggests that overexpression of OsiSAP1 in transgenic rice results in altered expression of several endogenous genes including those coding for transcription factors, membrane transporters, signaling components and genes involved in metabolism, growth and development. A total of 150 genes were found to be more than twofold up-regulated in transgenic rice of which 43 genes are known to be involved in stress response. Our results suggest that OsiSAP1 is a positive regulator of water-deficit stress tolerance in rice.Plant Cell Reports 06/2014; 33(9). · 2.94 Impact Factor
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ABSTRACT: Global production of rice (Oryza sativa) grain is limited by water availability and the low 'leaf-level' photosynthetic capacity of many cultivars. Oryza sativa is extremely susceptible to water-deficits; therefore, predicted increases in the frequency and duration of drought events, combined with future rises in global temperatures and food demand, necessitate the development of more productive and drought tolerant cultivars. We investigated the underlying physiological, isotopic and morphological responses to water-deficit in seven common varieties of O. sativa, subjected to prolonged drought of varying intensities, for phenotyping purposes in open field conditions. Significant variation was observed in leaf-level photosynthesis rates (A) under both water treatments. Yield and A were influenced by the conductance of the mesophyll layer to CO2 (gm) and not by stomatal conductance (gs). Mesophyll conductance declined during drought to differing extents among the cultivars; those varieties that maintained gm during water-deficit sustained A and yield to a greater extent. However, the variety with the highest gm and yield under well-watered conditions (IR55419-04) was distinct from the most effective cultivar under drought (Vandana). Mesophyll conductance most effectively characterises the photosynthetic capacity and yield of O. sativa cultivars under both well-watered and water-deficit conditions; however, the desired attributes of high gm during optimal growth conditions and the capacity for gm to remain constant during water-deficit may be mutually exclusive. Nonetheless, future genetic and physiological studies aimed at enhancing O. sativa yield and drought stress tolerance should investigate the biochemistry and morphology of the interface between the sub-stomatal pore and mesophyll layer.PLoS ONE 10/2014; 9(10):e109054. · 3.53 Impact Factor