Tolerance to drought is a quantitative trait, with a complex phenotype, often confounded by plant phenology. Breeding for drought tolerance is further complicated since several types of abiotic stress, such as high temperatures, high irradiance, and nutrient toxicities or deficiencies can challenge crop plants simultaneously. Although marker-assisted selection is now widely deployed in wheat, it has not contributed significantly to cultivar improvement for adaptation to low-yielding environments and breeding has relied largely on direct phenotypic selection for improved performance in these difficult environments. The limited success of the physiological and molecular breeding approaches now suggests that a careful rethink is needed of our strategies in order to understand better and breed for drought tolerance. A research programme for increasing drought tolerance of wheat should tackle the problem in a multi-disciplinary approach, considering interaction between multiple stresses and plant phenology, and integrating the physiological dissection of drought-tolerance traits and the genetic and genomics tools, such as quantitative trait loci (QTL), microarrays, and transgenic crops. In this paper, recent advances in the genetics and genomics of drought tolerance in wheat and barley are reviewed and used as a base for revisiting approaches to analyse drought tolerance in wheat. A strategy is then described where a specific environment is targeted and appropriate germplasm adapted to the chosen environment is selected, based on extensive definition of the morpho-physiological and molecular mechanisms of tolerance of the parents. This information was used to create structured populations and develop models for QTL analysis and positional cloning.

/pdf/genetic-and-genomic-tools-to-improve-drought-tolerance-in-4r2sqvv6ha.pdf

Genetic and genomic tools to improve drought tolerance in wheat

This review addresses possible adaptation strategies in rice production to abiotic stresses that will aggravate under climate change: heat (high temperature and humidity), drought, salinity, and submergence. Each stress is discussed regarding the current state of knowledge on damage mechanism for rice plants as well as possible developments in germplasm and crop management technologies to overcome production losses. Higher temperatures can adversely affect rice yields through two principal pathways, namely (i) high maximum temperatures that cause—in combination with high humidity—spikelet sterility and adversely affect grain quality and (ii) increased nighttime temperatures that may reduce assimilate accumulation. On the other hand, some rice cultivars are grown in extremely hot environments, so that the development of rice germplasm with improved heat resistance can capture an enormous genetic pool for this trait. Likewise, drought is a common phenomenon in many rice growing environments, and agriculture research has achieved considerable progress in terms of germplasm improvement and crop management (i.e., water saving techniques) to cope with the complexity of the drought syndrome. Rice is highly sensitive to salinity. Salinity often coincides with other stresses in rice production, namely drought in inland areas or submergence in coastal areas. Submergence tolerance of rice plants has substantially been improved by introgressing the Sub1 gene into popular rice cultivars in many Asian rice growing areas. Finally, the review comprises a comparative assessment of the rice versus other crops related to climate change. The rice crop has many unique features in terms of susceptibility and adaptation to climate change impacts due to its semiaquatic phylogenetic origin. The bulk of global rice supply originates from irrigated systems which are to some extent shielded from immediate drought effects. The buffer effect of irrigation against climate change impacts, however, will depend on nature and state of the respective irrigation system. The envisaged propagation of irrigation water saving techniques will entail benefits for the resilience of rice production systems to future droughts. We conclude that there are considerable risks for rice production stemming from climate change, but that the development of necessary adaptation options can capitalize on an enormous variety of rice production systems in very different climates and on encouraging progress in recent research.

Climate change affecting rice production: the physiological and agronomic basis for possible adaptation strategies

Plants face a combination of different abiotic stresses under field conditions which are lethal to plant growth and production. Simultaneous occurrence of chilling and drought stresses in plants due to the drastic and rapid global climate changes, can alter the morphological, physiological and molecular responses. Both these stresses adversely affect the plant growth and yields due to physical damages, physiological and biochemical disruptions, and molecular changes. In general, the co-occurrence of chilling and drought combination is even worse for crop production rather than an individual stress condition. Plants attain various common and different physiological and molecular protective approaches for tolerance under chilling and drought stresses. Nevertheless, plant responses to a combination of chilling and drought stresses are unique from those to individual stress. In the present review, we summarized the recent evidence on plant responses to chilling and drought stresses on shared as well as unique basis and tried to find a common thread potentially underlying these responses. We addressed the possible cross talk between plant responses to these stresses and discussed the potential management strategies for regulating the mechanisms of plant tolerance to drought and/or chilling stresses. To date, various novel approaches have been tested in minimizing the negative effects of combine stresses. Despite of the main improvements there is still a big room for improvement in combination of drought and chilling tolerance. Thus, future researches particularly using biotechnological and molecular approaches should be carried out to develop genetically engineered plants with enhanced tolerance against these stress factors.

/pdf/chilling-and-drought-stresses-in-crop-plants-implications-3zvxfs5ueg.pdf

Chilling and Drought Stresses in Crop Plants: Implications, Cross Talk, and Potential Management Opportunities

Phenotypic and genotypic analysis of drought-resistance traits for development of rice cultivars adapted to rainfed environments

Rice is the staple food and rice production consumes about 50% of the fresh water resources in China. In addition, drought is one of the most important constraints in rice resulting in large yield losses and limiting the average yield increase of the country. There is an urgent need to enhance water-saving (W) capacity or drought resistance (DR) of rice. WDR varieties can be developed through introgressing the water-saving and drought resistance capacity mainly from the traditional upland to the commercialized paddy rice cultivars. The breeding target is a high yield potential under irrigation, an acceptable grain quality, and water consumption reduced by about 50% compared with paddy rice. In a water-limited environment, a higher level of drought resistance and reduced yield loss by drought stress are required. In recent years, the field drought-resistance screening facility was established and the evaluation standard was developed. Some DR rice varieties were identified and used in both molecular mapping and breeding programmes. Several WDR varieties were developed and released to farmers. This article describes our initial achievement towards this goal and provides some details on the rationale and the specific steps and methods used.

Ks S. Fischer

Papers

Use of drought response index for identification of drought tolerant genotypes in rainfed lowland rice