Rice development and water demand under drought stress imposed at distinct growth stages.

2016

Drought impact on rainfed common bean production areas in Brazil.

Common bean production in Goiás, Brazil is concentrated in the same geographic area, but spread acrossthree distinct growing seasons, namely, wet, dry and winter. In the wet and dry seasons, common beansare grown under rainfed conditions, whereas the winter sowing is fully irrigated. The conventional breed-ing program performs all varietal selection stages solely in the winter season, with rainfed environmentsbeing incorporated in the breeding scheme only through the multi environment trials (METs) wherebasically only yield is recorded. As yield is the result of many interacting processes, it is challengingto determine the events (abiotic or biotic) associated with yield reduction in the rainfed environments(wet and dry seasons). To improve our understanding of rainfed dry bean production so as to produceinformation that can assist breeders in their efforts to develop stress-tolerant, high-yielding germplasm,we characterized environments by integrating weather, soil, crop and management factors using cropsimulation models. Crop simulations based on two commonly grown cultivars (Pérola and BRS Radi-ante) and statistical analyses of simulated yield suggest that both rainfed seasons, wet and dry, can bedivided in two groups of environments: highly favorable environment and favorable environment. Forthe wet and dry seasons, the highly favorable environment represents 44% and 58% of production area,respectively. Across all rainfed environment groups, terminal and/or reproductive drought stress occursin roughly one fourth of the seasons (23.9% for Pérola and 24.7% for Radiante), with drought being mostlimiting in the favorable environment group in the dry TPE. Based on our results, we argue that eventhough drought-tailoring might not be warranted, the common bean breeding program should adapttheir selection practices to the range of stresses occurring in the rainfed TPEs to select genotypes moresuitable for these environments.

Plasticity in leaf-level water relations of tropical rainforest trees in response to experimental drought.

The tropics are predicted to become warmer and drier, and understanding the sensitivity of tree species to drought is important for characterizing the risk to forests of climate change. This study makes use of a long-term drought experiment in the Amazon rainforest to evaluate the role of leaf-level water relations, leaf anatomy and their plasticity in response to drought in six tree genera. The variables (osmotic potential at full turgor, turgor loss point, capacitance, elastic modulus, relative water content and saturated water content) were compared between seasons and between plots (control and through-fall exclusion) enabling a comparison between short- and long-term plasticity in traits. Leaf anatomical traits were correlated with water relation parameters to determine whether water relations differed among tissues. The key findings were: osmotic adjustment occurred in response to the long-term drought treatment; species resistant to drought stress showed less osmotic adjustment than drought-sensitive species; and water relation traits were correlated with tissue properties, especially the thickness of the abaxial epidermis and the spongy mesophyll. These findings demonstrate that cell-level water relation traits can acclimate to long-term water stress, and highlight the limitations of extrapolating the results of short-term studies to temporal scales associated with climate change.

Challenges and difficulties on water stress experiment designs, database and modeling for drought tolerance phenotyping.

2008

Spondias tuberosa trees grown in tropical, wet environments are more susceptible to drought than those grown in arid environments.

In this study, we investigated the different responses of Spondias tuberosa (umbu) trees, which grow in two different ecological life zones in northeast Brazil: tropical wet and tropical arid ecosystems. We evaluated the responses of plants grown under humid and dry conditions by measuring the photosynthesis, water status, fluorescence parameters, carbon isotopes and antioxidant system activity. The higher net photosynthesis values were recorded contemporaneously with the lower VPD values. The highest internal-to-ambient CO2 concentration and the absence of typical changes in the fluorescence parameters suggested an onset of a nonstomatal limitation in the photosynthesis. Our results showed that umbu plants can adjust their antioxidant activity during the dry season as a defensive strategy against the deleterious effects of water stress. This evidence is supported by the observed modifications in the pigment concentrations, increased accumulation of hydrogen peroxide and malondialdehyde, high levels of electrolyte leakage, increased antioxidant activity, and decreased carbon isotope discrimination in the umbu trees during the dry season. Supported by multivariate analysis of variance, significantly effect of interaction between categorical months of collect and location predicts a strong ?dry season effect? on our dataset. Taken together, our data show that umbu trees grown in a wet tropical environment are more susceptible to drought, as compared with their tropical arid counterparts.

Expression of rice genes homologous of Arabidopsis genes previously related to drought tolerance.

The identification and validation of candidate genes related to traits of interest is a time consuming and expensive process and the homology among genes from different species can facilitate the identification of genes of the target species from the genomic information of a model species. This study aimed to quantify the expression of homologous rice genes previously related to drought tolerance in Arabidopsis. Five genes (CPK6, PLDa, GluR2, CesA8, and EIN2) were identified in rice by the homology of the amino acid sequence between rice and Arabidopsis. The genotypes Douradão (drought tolerant) and Primavera (drought susceptible) were subjected to a water deficit experiment, and subsequently evaluated for gene expression by qPCR for the five homologous and Lsi1 genes. The qPCR analysis clearly showed that the five homologous genes were expressed in rice, which is an indication that these genes could preserve their function in rice as a response to drought. In Douradão, of the five homologous genes, all but OsGluR2 displayed an increase in the average expression in drought treatment when compared to the control, while in Primavera, the average expression of the five genes did not differ between the control and drought treatment. In Douradão, the OsPLDa1, which showed the higher expression level in drought in relation to the control (10.82), significantly increased the gene expression in the leaf and root tissues as a response to drought, in both vegetative and reproductive stages, whereas in Primavera, this gene was suppressed in both tissues and stages under drought. Therefore, the OsPLDa1 gene was the most important in relation to drought response and is an interesting candidate for further studies in developing rice cultivars that are more tolerant to this stress.