Statistical Databases

Improving crops yield under water-limited conditions is the most daunting challenge faced by breeders. To this end, accurate, relevant phenotyping plays an increasingly pivotal role for the selection of drought-resilient genotypes and, more in general, for a meaningful dissection of the quantitative genetic landscape that underscores the adaptive response of crops to drought. A major and universally recognized obstacle to a more effective translation of the results produced by drought-related studies into improved cultivars is the difficulty in properly phenotyping in a high-throughput fashion in order to identify the quantitative trait loci that govern yield and related traits across different water regimes. This review provides basic principles and a broad set of references useful for the management of phenotyping practices for the study and genetic dissection of drought tolerance and, ultimately, for the release of drought-tolerant cultivars.

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Phenotyping for drought tolerance of crops in the genomics era.

Here we highlight how both the root and shoot environment impact on whole plant hormone balance, particularly under stresses such as soil drying, and relate hormone ratios and relative abundances to processes influencing plant performance and yield under both mild and more severe stress. We discuss evidence (i) that abscisic acid (ABA) and ethylene act antagonistically on grain-filling rate amongst other yield-impacting processes; (ii) that ABA's effectiveness as an agent of stomatal closure can be modulated by coincident ethylene or cytokinin accumulation; and (iii) that enhanced cytokinin production can increase growth and yield by improving foliar stay-green indices under stress, and by improving processes that impact grain-filling and number, and that this can be the result of altered relative abundances of cytokinin and ABA (and other hormones). We describe evidence and novel processes whereby these phenomena are/could be amenable to manipulation through genetic and management routes, such that plant performance and yield can be improved. We explore the possibility that a range of ABA-ethylene and ABA-cytokinin relative abundances could represent targets for breeding/managing for yield resilience under a spectrum of stress levels between severe and mild, and could circumvent some of the pitfalls so far encountered in the massive research effort towards breeding for increases in the complex trait of yield.

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Plant hormone interactions: innovative targets for crop breeding and management

Drought has been one of the most important limiting factors for crop production, which deleteriously affects food security worldwide. The main objective of the present study was to quantitatively assess the effect of drought on the agronomic traits (e.g., plant height, biomass, yield, and yield components) of rice and wheat in combination with several moderators (e.g., drought stress intensity, rooting environment, and growth stage) using a meta-analysis study. The database was created from 55 published studies on rice and 60 published studies on wheat. The results demonstrated that drought decreased the agronomic traits differently between rice and wheat among varying growth stages. Wheat and rice yields decreased by 27.5% and 25.4%, respectively. Wheat grown in pots showed greater decreases in agronomic traits than those grown in the field. Rice showed opposite growing patterns when compared to wheat in rooting environments. The effect of drought on rice increased with plant growth and drought had larger detrimental influences during the reproductive phase (e.g., blooming stage, filling stage, and maturity). However, an exception was found in wheat, which had similar decreased performance during the complete growth cycle. Based on these results, future droughts could produce lower yields of rice and wheat when compared to the current drought.

Effect of Drought on Agronomic Traits of Rice and Wheat: A Meta-Analysis

The solubility of Cd in contaminated paddy soils controls Cd uptake by rice, which is an important food safety issue. We investigated the solution and solid-phase dynamics of Cd in a paddy soil spiked with ∼20 mg kg(-1) Cd during 40 days of soil reduction followed by 28 days of soil reoxidation as a function of the amounts of sulfate available for microbial reduction and of Cu that competes with Cd for precipitation with biogenic sulfide. At an excess of sulfate over (Cd + Cu), dissolved Cd decreased during sulfate reduction and Cd was transformed into a poorly soluble phase identified as Cd-sulfide using Cd K-edge X-ray absorption spectroscopy (XAS). The extent of Cd-sulfide precipitation decreased with decreasing sulfate and increasing Cu contents, even if sulfate exceeded Cd. When both Cu and Cd exceeded sulfate, dissolved and mobilizable Cd remained elevated after 40 days of soil reduction. During soil reoxidation, Cd-sulfide was readily transformed back into more soluble species. Our data suggest that Cd-sulfide formation in flooded paddy soil may be limited when the amounts of Cd and other chalcophile metals significantly exceed reducible sulfate Therefore, in multimetal contaminated paddy soils with low sulfate contents, Cd may remain labile during soil flooding, which enhances the risk for Cd transfer into rice.

Redox-Controlled Changes in Cadmium Solubility and Solid-Phase Speciation in a Paddy Soil As Affected by Reducible Sulfate and Copper

Hormones in the grains and roots in relation to post-anthesis development of inferior and superior spikelets in japonica/indica hybrid rice.

BACKGROUND: Rice is the most important staple food in Asia but has also been identified as one of the major sources of cadmium (Cd) intakes for some Asian population. This study investigated whether grain yield could be maintained but Cd in grains be reduced through proper irrigation management when rice was grown in Cd-contaminated soil.

RESULTS: Compared to the well watered treatment, the alternate wetting and moderate soil drying (MD, re-watered when soil water potential decreased to −20 kPa) increased grain yield by 10–12% and improved milling and appearance quality of rice when grown in a soil containing a water-soluble Cd content of 18 g kg−1. An alternate wetting and severe soil drying (SD, re-watered when soil water potential decreased to −40 kPa) showed an opposite effect. Both MD and SD significantly increased Cd content in roots while they reduced it in the straw. MD reduced Cd content by 19–21% in the grain and by 40% in milled rice. The SD significantly increased Cd content in the grain but reduced it in milled rice.

CONCLUSION: An alternate wetting and moderate soil drying could increase rice yield and quality and also reduce Cd in the diet of rice. Copyright © 2009 Society of Chemical Industry

Alternate wetting and moderate soil drying increases grain yield and reduces cadmium accumulation in rice grains.

The possible relationship between the levels of ethylene and 1-aminocylopropane-1-carboxylic acid (ACC) in the grains and the quality of rice (Oryzasativa L.) were investigated by using 12 rice cultivars. The results showed that both the ethylene evolution rate and ACC content in grains during the grain filling period correlated negatively with head rice production and positively with chalky kernels, chalky size, and chalkiness. The levels of ethylene and ACC were not significantly correlated with alkali spreading value and amylose content. Application of ethephon, an ethylene-releasing agent, or ACC to panicles at the early grain filling stage significantly reduced the rates of brown rice, milled rice, and head rice, and significantly increased the percentage of chalky kernels, chalky size, and chalkiness. Application of aminoethoxyvinylglycine, an inhibitor of ACC synthase, had the opposite effect. Chalkiness appears to be a senescence related phenomenon which is stimulated by ethylene. The results suggest that ethylene and ACC in grains play an important role in regulating rice quality, and that grain appearance and milling quality would be improved though the reduction of ethylene and ACC in grains during grain filling.

Ethylene and ACC levels in developing grains are related to the poor appearance and milling quality of rice

Post-Anthesis Changes in Concentrations of Polyamines in Superior and Inferior Spikelets and Their Relation with Grain Filling of Super Rice: Post-Anthesis Changes in Concentrations of Polyamines in Superior and Inferior Spikelets and Their Relation with Grain Filling of Super Rice

Gui-Lu Tan

Papers

Hormones in the grains and roots in relation to post-anthesis development of inferior and superior spikelets in japonica/indica hybrid rice.

Alternate wetting and moderate soil drying increases grain yield and reduces cadmium accumulation in rice grains.

Ethylene and ACC levels in developing grains are related to the poor appearance and milling quality of rice

Post-Anthesis Changes in Concentrations of Polyamines in Superior and Inferior Spikelets and Their Relation with Grain Filling of Super Rice: Post-Anthesis Changes in Concentrations of Polyamines in Superior and Inferior Spikelets and Their Relation with Grain Filling of Super Rice

Changes in Grain Yield and Morphological and Physiological Characteristics During 60-Year Evolution of Japonica Rice Cultivars in Jiangsu