Selection Criteria For Drought Resistance Research Articles

Estimation of Drought Tolerance Indices in Upland Cotton under Water Deficit Conditions

Cotton is a precious commodity that offers raw material to the textile industry. This crop is grown in tropical and sub-tropical regions of the world. Abiotic stresses exerts negative impact on cotton production, but water scarcity has the worst impact. It is rising due to current situation, in which global warming is producing a decrease in precipitation while an increase in evapo-transpiration is causing an agricultural drought. Thus, it is a difficult task for cotton breeders to identify cotton lines that can respond to areas with limited water supplies without lowering yields and might be utilized as suitable parents in a breeding program to produce drought-tolerant indices. The primary objective of this research was the estimation of drought tolerance indices in upland cotton under water deficit conditions. For this purpose, fifty accessions of upland cotton were assessed for their ability to tolerate the water stress under three conditions, namely control, 50% FC, and 75% FC. These genotypes showed significant variations based on morpho-physiological and biochemical characteristics. At control conditions, these genotypes exhibited enhanced growth and better performance. Whereas, the behavior of some indices under 75% FC showed less growth as compared to control, while under the 50% FC highly significant reductions were observed among genotypes. The genotypes that are resistant to drought and those that are susceptible were found using the K-means cluster and biplot analysis. In terms of performance, the genotypes namely Cyto-515, CIM-595, FH-142, and IR-3701 exhibited relatively better in all the treatments and low excised leaf water loss, high relative water contents, chlorophyll contents, free proline contents, and peroxidase activity were observed to be useful selection criteria for drought resistance. These identified genotypes namely, Cyto-515, CIM-595, FH-142, and IR-3701 may be grown in water deficit areas of the country to assess their potential, could be used in breeding programs for development of germplasm suitable for water stress conditions.

Physiological traits associated with drought resistance in Andean and Mesoamerican genotypes of common bean (Phaseolus vulgaris L.)

Common bean (Phaseolus vulgaris L.) is the most important grain legume for human consumption, and drought stress affects over 60 % of dry bean production worldwide. Field and rainout shelter studies were conducted at the International Center for Tropical Agriculture (CIAT), Palmira, Colombia to (i) evaluate phenotypic differences in drought resistance in Andean and Mesoamerican gene pools, (ii) identify genotypes of both Andean and Mesoamerican with superior drought resistance, and (iii) identify phenotypic traits that may be useful for breeding to improve drought resistance in common bean. A total of 24 bean genotypes, twelve genotypes belonging to Mesoamerican gene pool and twelve to Andean gene pool were evaluated under field with two levels of water supply (irrigated and rainfed) and managed drought under rainout shelter conditions. Results showed that five Mesoamerican lines SEA 5, SEA 15, SER 22, SER 16, SER 8 and one Andean line SEQ 1003 have superior resistance to drought. The superior performance of these lines under drought stress was associated with better canopy biomass at mid-pod filling that could be related to deeper root system and effective use of water, combined with efficient remobilization of photosynthates from vegetative structures to pod development (pod partitioning index, PPI) and grain filling (pod harvest index, PHI). Pod harvest index could be a useful selection criteria for drought resistance, to improve the efficiency of breeding programs for selecting superior genotypes of common bean.

Evaluation of and selection criteria for drought resistance in Chinese semiwinter rapeseed varieties at different developmental stages

AbstractThe impacts of water deficit imposed at either the germination stage or the reproductive stage on biological traits of 37 semiwinter rapeseed varieties were analysed. The osmotic stress induced by 14% polyethylene glycol had a substantial impact on seed germination and caused significant reductions in plant growth and seed vigour. Relative water content was identified as a good indicator for early screening of drought resistance. At the reproductive stage, seed yield, 1000‐seed weight, height of the first branch, plant height and number of pods per plant were all markedly reduced under the exceptionally long and severe drought condition. Two of the top three resistant genotypes at the germination stage were also shown to be resistant based on the drought susceptibility index for seed yield. Phenotypic correlation and path analyses were employed to rank the relative importance of other agronomic traits with regard to seed yield. The important contributors to seed yield under drought conditions, in descending order, were as follows: 1000‐seed weight, days to maturity, number of pods per plant and plant height.

Identification of two functional markers associated with drought resistance in maize

Drought is recognized as the major abiotic constraint to global food production. Molecular markers have become an important genetic tool for understanding genome dynamics and facilitating molecular breeding of drought resistance. Here, cleaved amplified polymorphic sequence (CAPS) markers dhnC397 and rspC1090 were identified based on the SNP A/G polymorphisms in the drought-resistance genes dhn1 and rsp41. The two alleles of both genes were easily and rapidly discriminated by polyacrylamide gel electrophoresis to reveal single nucleotide polymorphisms (SNPs) as functional markers. By validation of an integrated selection criterion for drought resistance, the average SI (selection index for drought resistance) of lines with superior drought-resistance genotypes was higher than those with opposite, less drought-resistant genotypes, and the SI of heterotic group B was higher than that of heterotic group A for both genes. Integrating the results of CAPS analysis and evaluation of drought resistance indicated that the SNPs in these two genes partly participate in conferring drought resistance in these maize lines of interest. Breeders can thus use the CAPS markers identified here as functional markers for the improvement of drought resistance in these maize lines and possibly others.

Early Osmotic Adjustment Responses in Drought‐Resistant and Drought‐Sensitive Oilseed Rape

The impact of osmotic stress on growth, physiology, and metabolism of winter oilseed rape (Brassica napus L.) was investigated by detailed analysis of biomass traits, hormone metabolites and osmolytes in two genetically unrelated drought-tolerant genotypes and two unrelated drought-sensitive genotypes. Seedlings were grown in vitro under controlled conditions and osmotic stress was simulated by applying a gradual treatment with polyethylene glycol (PEG 6000), followed by hypo-osmotic treatment of variants used for metabolite determination. The results provide a basis for the identification of reliable selection criteria for drought resistance in oilseed rape. The in vitro cultivation system established during this study enabled effective discrimination of early osmotic stress responses between drought-resistant and -susceptible oilseed rape genotypes that also show large differences in relative seed yield under drought conditions in the field. Clear physiological and metabolic differences were observed between the drought-resistant and drought-sensitive genotypes, suggesting that osmotic adjustment is a key component of drought response in oilseed rape. Unexpectedly, however, the drought-resistant genotypes did not show typical hormonal adjustment and osmolyte accumulation, suggesting that they possess alternative physiological mechanisms enabling avoidance of stress symptoms.

A proposed selection criterion for drought resistance across multiple environments in maize

Drought resistance is a complex quantitative trait, involving interactions of many metabolic pathways related to stress-resistant genes. Identification of a standard evaluation assay has been the most pressing problem for selection of drought-resistant genotypes and ultimately for elucidating the internal genetic mechanisms. A field phenotypic investigation was performed on more than 20 morphological traits and grain yield and its components for 201 Chinese common inbred maize (Zea mays L.) lines under water deficit in seven environments. An integrated selection criterion for drought resistance was proposed and used to identify drought-resistant maize genotypes. In it, six traits including grain yield, ear number per plant, kernel number per ear, plant height, anthesis–silking interval and degree of leaf curling were chosen as the most relevant factors related to drought resistance, as determined by statistical analysis. The integrated selection criterion was highly correlated with grain yield under both well-watered and water-stressed regimes, and was also highly correlated with other commonly used selection criteria. Moreover, for 128 (63.7%) inbred lines the evaluation result with this criterion was consistent across more than three environments thus avoiding the effect of genotype–environment interaction, though stress level between the different environments largely fluctuated. There were 43 inbred lines evaluated for drought-resistance and most were bred during 1990–2000. The criterion will be useful to identify excellent drought-resistant genotypes in future maize molecular breeding programs.

Water relations and gas exchange in young coconut palm (Cocos nuciferaL.) as influenced by water deficit

Drought is the main climatic limitation to coconut palm (Cocos nucifera L.) production. To identify early screening parameters for drought resistance, physiological responses to water deficit were investigated for the first time using containerized young plants grown outside. Three varieties were studied: 'West Coast Tall' (drought avoiding), 'Malayan Yellow Dwarf' (drought susceptible), and their progeny, the hybrid 'PB 121' (drought resistant). Leaf water status (relative water content, leaf water potential) and leaf gas exchange parameters (stomatal conductance to water vapor, net photosynthetic rate, and leaf internal CO2concentration) were measured throughout a drying cycle induced by withholding watering. On fully hydrated plants, the sensitivity of stomata to atmospheric water vapor deficit was also investigated. In the three varieties, stomatal conductance to water vapor declined before leaf water status parameters were affected. The existence of a root-to-shoot communication system was proposed. Net photosynthetic rate was highly dependent on stomatal aperture, but nonstomatal factors also participated in the reduction of CO2fixation. Since gas exchange rates were equally sensitive to drought in the three varieties, they could not be used as screening parameters for drought resistance. Under severe drought stress, both relative water content and leaf water potential differed significantly among populations. 'West Coast Tall' maintained a higher leaf water status than 'Malayan Yellow Dwarf'. Remarkably, the water status parameters of 'PB 121' were intermediate between those of the two parents. Similar ranking was obtained in experiments with excised leaflets. The high reproductibility of the results suggests that leaf water status parameters might be useful as early selection criteria for drought resistance in coconut palm. Key words: Cocos nucifera L., gas exchange, leaf water status parameters, water deficit, water relations.

Improving Common Bean Performance under Drought Stress

Drought is the second major constraint to common bean (Phaseolus vulgaris L) production after disease. This study examined yield under drought, yield potential, drought susceptibility index, harvest index, and geometric mean as potential indicators of drought resistant genotypes. The performance of two common bean populations, consisting of 78 and 95 recombinant inbred lines, was examined under moisture stress and nonstress regimes. Experiments were conducted at seven locations (1990–1994) in Michigan and Mexico to identify effective selection criteria for drought resistance. Two genotypes from each population yielded in the top 10% under both stress and nonstress conditions. Heritability estimates for yield in the Sierra/AC1028 population, based on 5 yr of data, ranged from 0.55 to 0.59 for stress and nonstress, respectively, and from 0.20 to 0.19 for stress and nonstress, respectively, in the Sierra/Lef‐2RB population. Heritability for plant biomass was 0.52 for stress and 0.55 for nonstress in the Sierra/AC1028 population and 0.15 under stress and 0.05 under nonstress in the Sierra/Lef‐2RB population. One‐hundred seed weight was the most highly heritable trait in both populations with heritability estimates of 0.80 for the Sierra/AC1028 population and 0.65 for the Sierra/Lef‐2RB population. The geometric mean of the two moisture regimes was the single strongest indicator of performance under stress and nonstress, and a breeding strategy that involves selection based first on the geometric mean, followed by selection based on yield under stress, was suggested as the most effective strategy to improve drought resistance in common bean.

Water‐retention capability as a selection criteria for drought resistance in wheat

Abstract Four durum wheat cultlvars (Triticum turgidum spp. durum Desf.) from different countries of origin (Austria, Ethiopia, and Italy) were investigated. Plants were grown in pots under glasshouse conditions. Immediately after the full development of the flag leaves, these leaves were detached for the screening. Distinct differences in water‐retention capabilty among the cultivars was observed. The drought‐resistant (hardy) types, Valgerardo and Boohai, showed better water retention capabilty than the drought‐sensitive ones, such as DZ‐04–688. Poor yielding cultivars under field conditions were also found to be poor in water‐retention capability and vice versa. The applied method is simple and inexpensive. It adds another procedure when screening for drought resistance. However, it needs further confirmation by cultivars covering a broader range of genetic diversity.

Phenotypic Diversity and Associations of Some Potentially Drought‐responsive Characters in Durum Wheat

Genetic improvement of crop plants for drought resistance is hindered by lack of information on variability and associations of drought‐response characters in breeding materials. We evaluated 3430 accessions in a world collection of durum wheat (Triticum turgidum L. var. durum) for 19 characters under severe moisture‐limiting field conditions at Swift Current, SK, Canada in 1984. Phenotypic diversity (H) and multicharacter associations were investigated in germplasm from nine durum wheat growing regions. The Middle East was one of the regions with a high level of diversity (H = 1.132). The rate of excised‐leaf water loss (RWL) was used as a possible indicator of drought resistance. Glaucousness, plant height, chlorotic leaf spots, days to flowering, and days to maturity were significantly associated with RWL in six to seven regions. The discrete multivariate log‐linear analysis involving these six characters revealed the first order (two‐character) and some second‐order (three‐character) associations. These five characters were chosen along with RWL as drought‐response characters that may be useful for establishing selection criteria for drought resistance. These results have important implications for developing durum wheat ideo‐types for high and stable production in drought‐prone environments.

Water Relations in Winter Wheat as Drought Resistance Indicators

Although drought is recognized as an important limitation to wheat (Triticum aestivum L.) production in many regions, drought resistance selection techniques are not adequately developed. In 1984–1985 and 1985–1986, field experiments were conducted in Stillwater, OK, to determine potential drought resistance parameters and their inheritance in winter wheat. Single plants of drought resistant ‘TAM W‐101’ and drought susceptible ‘Sturdy’, their F1 and F2 progeny, and backcrosses of the F1 to each parent were evaluated under a rain shelter. Tiller number was recorded throughout the growing season. As stress developed during reproductive development, water potential (WP), solute potential (SP), turgor potential (TP), relative water content (RWC) were measured at 7‐ to 10‐d intervals on single leaves until tlag leaf senescence. Tiller number and growth rate were similar among the six populations. Water potential, WP components, and RWC declined with increasing drought stress, but no significant differences among populations were found, in WP, SP, or TP. Relative water content differed significantly among populations under increasing drought stress. TAM W‐101 maintained a higher RWC under drought conditions than Sturdy, and had a longer grain‐filling period. Comparison of the RWC values among populations indicated that differences were controlled predominantly by genes with additive effects. Narrow‐sense heritability (h2) of RWC increased as drought stress intensified and reached a maximum value of 0.64 1 wk prior to flag leaf senescence. With this high h2, RWC shows promise as a selection criterion for drought resistance in winter wheat.

Growth Habits of Water-stressed Wheat Seedlings as Selection Criteria for Drought Resistance

Growth Habits of Water-stressed Wheat Seedlings as Selection Criteria for Drought Resistance

Genetic and physiological relationships in plant breeding for drought resistance

The genetic improvement of plant drought resistance by the selection for yield under stress is a possible but a prolonged and problematic procedure. Recent developments in the understanding of the physiological responses of plants to water stress and their associations with plant productivity allow to embark upon experimental selection programs that employ physiological selection criteria for drought resistance. This is supported by the recent developments of rapid selection techniques for several physiological components of drought resistance. It is, however, emphasized that such selection programs should be approached as the best available approximation, rather than established proven routines, for each crop and environment. The deployment of such experimental selection systems is important not only as a probable base for progress in selection but also as a feedback generator of important genetic and physiological information, to be used for further improvement of the selection systems. Several rapid physiological selection techniques are briefly reviewed, and examples of their logistic incorporation into a routine breeding program are given.

Genetic analysis of drought stress response in rapeseed (Brassica campestris and B. Napus). III. physiological characters

Leaf proline accumulation, leaf chlorophyll stability, and germination at low osmotic potentials have previously been suggested as possible selection criteria for drought resistance in turnip rape (Brassica campestris) and rapeseed (B. napus) (Richards, 1978a). The feasibility of using these characters in a breeding program is reported. These characters were under significant genetic control and were responsive to selection. Broad sense heritabilities ranged from 40% for proline accumulation in both species to 55% for germination rate in B. campestris and 64% for chlorophyll stability in B. napus, however, narrow sense heritabilities for proline and germination were substantially lower. Their use as selection criteria for yield in a Mediteranean drought would be restricted since in B. campestris these characters were not related to yield while in B. napus only a weak association was observed between yield under drought and proline accumulation.

Variation between and within species of rapeseed (Brassica campestris and B. napus) in response to drought stress III. Physiological and physicochemical characters

Genotypic variation in physiological and physicochemical parameters associated with drought resistance was observed between cultivars in Brassica napus and B. campestris. Significant variation in proline accumulation, chlorophyll stability, germination rate and percentage, relative turgidity, growth rates and water use efficiency were found in plants grown under simulated drought conditions in a glasshouse. No variation was detected between cultivars for leaf diffusive resistance or heat tolerance. A yield index for each cultivar was derived from yield performances in nine different field environments. Chlorophyll stability and proline accumulation in leaf tissue and germination percentage in solution equivalent to –17.5 bars osmotic potential was clearly related to this yield index in B. napus and to a lesser extent in B. campestris. The winter cultivars of B. napus also possessed drought resistance characteristics, and they may be a valuable resource for the development of cultivars for droughted environments. Parameters were measured in a glasshouse, prior to anthesis, and therefore offer potential as ancillary selection criteria for drought resistance in oilseed rape growing in Western Australia.