Sources Of Drought Tolerance Research Articles

Photosynthetic activity and metabolic profiling of bread wheat cultivars contrasting in drought tolerance.

The rapid increase in population growth under changing climatic conditions causes drought stress, threatening world food security. The identification of physiological and biochemical traits acting as yield-limiting factors in diverse germplasm is pre-requisite for genetic improvement under water-deficit conditions. The major aim of the present study was the identification of drought-tolerant wheat cultivars with a novel source of drought tolerance from local wheat germplasm. The study was conducted to screen 40 local wheat cultivars against drought stress at different growth stages. Barani-83, Blue Silver, Pak-81, and Pasban-90 containing shoot and root fresh weight >60% of control and shoot and root dry weight >80% and 70% of control, respectively, P (% of control >80 in shoot and >88 in root), K+ (>85% of control), and quantum yield of PSII > 90% of control under polyethylene glycol (PEG)-induced drought stress at seedling stage can be considered as tolerant, while more reduction in these parameters make FSD-08, Lasani-08, Punjab-96, and Sahar-06 as drought-sensitive cultivars. FSD-08 and Lasani-08 could not maintain growth and yield due to protoplasmic dehydration, decreased turgidity, cell enlargement, and cell division due to drought treatment at adult growth stage. Stability of leaf chlorophyll content (<20% decrease) reflects photosynthetic efficiency of tolerant cultivars, while ~30 µmol/g fwt concentration of proline, 100%-200% increase in free amino acids, and ~50% increase in accumulation of soluble sugars were associated with maintaining leaf water status by osmotic adjustment. Raw OJIP chlorophyll fluorescence curves revealed a decrease in fluorescence at O, J, I, and P steps in sensitive genotypes FSD-08 and Lasani-08, showing greater damage to photosynthetic machinery and greater decrease in JIP test parameters, performance index (PIABS), maximum quantum yield (Fv/Fm) associated with increase in Vj, absorption (ABS/RC), and dissipation per reaction center (DIo/RC) while a decrease in electron transport per reaction center (ETo/RC). During the present study, differential modifications in morpho-physiological, biochemical, and photosynthetic attributes that alleviate the damaging effects of drought stress in locally grown wheat cultivars were analyzed. Selected tolerant cultivars could be explored in various breeding programs to produce new wheat genotypes with adaptive traits to withstand water stress.

Drought Stress in Lentil (Lens culinaris, Medik) and Approaches for Its Management

Lentil plays an important role for food and nutritional security. It is a sustainable source of protein, zinc, iron, prebiotic carbohydrates, and diverse health-promoting nutrients. This crop is widely cultivated in semi-arid marginal areas and exposed to various environmental stressors. Drought stress is the major abiotic stress that causes serious effects on lentil growth and development. Thus, it is imperative to set up innovative and sustainable solutions to reduce the adverse effects of drought on lentil crop. In this review, the agro-morphological, physiological, and biochemical effects of drought on lentil were highlighted. Furthermore, breeding and agronomic interventions to improve lentil performance in drought-prone environments were also discussed. Overall, drought disturbs lentil germination, photosynthesis, water relations, shoot and root growth, thereby reducing final yield. Conventional breeding programs have identified several sources of drought tolerance; however, modern biotechnological tools could be adopted to decipher the genetic architecture of drought tolerance in lentil to accelerate the genetic progress. Cost-affordable and eco-friendly agronomic practices may also contribute to minimize the negative consequences of drought stress. Smart exploitation of breeding approaches and agronomic practices could help overcome drought, improve lentil productivity, and increase the profitability of farmers in dry areas.

Novel sources of drought tolerance in sorghum landraces revealed via the analyses of genotype-by-environment interactions.

Globally, sorghum is the fifth most important crop, which is used for food, feed and fuel. However, its production and productivity are severely limited by various stresses, including drought. Hence, this study aimed to determine the responses of different drought-tolerance related traits in the Ethiopian sorghum germplasm through multi-environment field trials, thereby identifying novel sources of germplasm that can be used for breeding the crop for drought-tolerance. Three hundred twenty sorghum landraces and four improved varieties were grown at three sites within drought-prone areas (Melkassa, Mieso and Mehoni) in Ethiopia. The targeted traits were chlorophyll content at flowering (CHLF), chlorophyll content at maturity (CHLM), green leaf number at flowering (GLNF), stay-green (SG), flag leaf area (FLA), peduncle length (PDL), and panicle exertion (PAE). Multi-variate analyses of the collected data revealed the presence of high phenotypic variation in all traits. The combined and AMMI Analysis of variance showed that phenotypic variation due to the genotypes was higher for SG, CHLM, CHLF and GLNF and lower for FLA, PE and PDL in comparison with variation due to the environments or genotype by environment interactions. High broad sense heritability was observed for CHLF, CHLM, SG, GLNF, FLA, and PDL, whereas PAE showed moderate heritability. Due to the high heritability of chlorophyll content and the relatively small effect of environmental factors on it, it could serve as a criterion for selecting desirable genotypes for drought-tolerant breeding in sorghum. It has been found that chlorophyll content has a significant positive correlation with stay-green and grain yield, indicating that high chlorophyll content contributes to increasing grain yield by delaying the process of leaf senescence. The analyses of AMMI, GGE biplot, and genotype selection index revealed that several sorghum landraces outperformed the improved varieties with respect to CHLF, CHLM, and SG. Such landraces could serve as novel sources of germplasm for improving drought tolerance through breeding.

Registration of Tx3440 through Tx3482 sorghum germplasm

AbstractThe sorghum [Sorghum bicolor (L.) Moench] germplasm lines Tx3440–Tx3482 (Reg. no. GP‐900–GP‐942, PI 695271–PI 695313) were developed and released by Texas A&amp;M AgriLife Research, Lubbock, TX, in 2020. Breeding crosses from these lines were made in Lubbock, TX, with grow‐out and selection of subsequent generations completed in breeding nurseries throughout Texas over a period of years. Once selected, these lines were test for agronomic performance in replicated trials across multiple locations and years. Within the set, Tx3340–Tx3482 represent diverse pedigrees and an array of combinations of grain color, plant color, and other agronomic traits. The lines are individually resistant to selected abiotic (pre‐ and/or post‐flowering drought) stress and biotic stress (grain weathering caused by diverse genera that include Fusarium spp., Curvularia spp., and Alternaria spp.; and anthracnose caused by Colletotrichum sublineola). These lines provide the sorghum industry with sources of drought tolerance, grain weathering, and anthracnose resistance in a diverse array of elite genetic backgrounds for use as seed parent lines for hybrid production and for new line development.

Assessment of the potential of wild Ipomoea spp. for the improvement of drought tolerance in cultivated sweetpotato Ipomoea batatas (L.) Lam

AbstractSweetpotato [Ipomoea batatas (L.) Lam] is cultivated worldwide, and it is a staple food in many developing countries. In some regions (e.g., Africa) drought is a major production constraint that results in significant yield loss. Climate change is predicted to result in even greater losses due to long periods of drought and elevated temperatures. The goal of this study was to assess the potential of wild Ipomoea spp. as a source of drought tolerance in cultivated sweetpotato. We evaluated the drought tolerance of I. batatas, I. cynanchifolia, I. leucantha, I. trifida and I. triloba in a randomized complete block design, with five levels of simulated drought: control (daily irrigation), and no irrigation for 7, 9, 21 and 50 days. We observed that post drought re‐irrigation of the wild species subjected to 21 days of stress resulted in plant recovery and an increase of the stomatal conductance of up to 99% in I. leucantha. However, under extreme stress (50 d) the wild plants did not respond to re‐irrigation, resulting in up to 89% (I. leucantha) plant mortality. The wild species did not produce storage roots, while the I. batatas cultivars produced storage roots. Under 50 days of stress I. batatas had a survival rate between 44% (cv. Tanzania) and 89% (cv. Beauregard). We concluded that the wild genotypes screened may not be a valuable source of germplasm for drought tolerance and that significant levels of drought tolerance may exist in cultivated sweetpotato.

Evaluation of U.S. inbred lines with expired plant variety protection for mid-altitude tropical maize breeding

Maize (Zea mays L.) inbred lines with expired U.S. Plant Variety Protection Act certificates (ex-PVPA) can be an important source of favorable alleles to improve grain yield, root and stalk lodging, drydown, plant architecture, and reduced time to maturity of tropical hybrids. Understanding the heterotic patterns and combining ability of ex-PVPA lines with tropical lines is necessary to design effective breeding strategies using this germplasm. This study evaluated 10 Iowa Stiff Stalk Synthetic (BSSS) and 11 Non-Stiff Stalk Synthetic (NSSS) inbred lines in hybrid combinations with tropical mid-altitude testers in five mid-altitude environments (900–2000 masl) in Mexico and identified six hybrids with grain yield equal or superior to that of the check hybrids. Two NSSS inbred lines: PHR03 and PHN82 had significant (P < 0.01) and positive general combining ability (GCA) effects with inbred lines from CIMMYT’s Tuxpeno heterotic group. Similarly, the BSSS line PHG39 had a significant positive GCA effect (P < 0.05) with non-Tuxpeno lines. The lines PHN82 and PHK29 had positive GCA effects (P < 0.01) under drought stress and could be used as sources of drought tolerance in CIMMYT breeding programs. The mid-altitude lines CML537 and CML539 had positive GCA effects (1.45 and 0.69 t/ha, respectively; P < 0.01) with NSSS lines whereas hybrids of CML384 with BSSS lines yielded 0.64 t/ha (P < 0.01) more than the average of the testcrosses. These results showed that U.S. ex-PVPA lines can increase grain yield of CIMMYT’s tropical mid-altitude hybrids.

PEDIGREE SELECTION IN BREAD WHEAT UNDER WATER DEFICIT FOR YIELD IN TOSHKA CONDITIONS

The present work aimed to study the effect of two cycles of pedigree selection for highly grain yield in two segregating populations of wheat under water stress, during the two winter seasons of 2015/2016 and 2016/2017at Toshka Research Station, Desert Research Center, Aswan, Egypt. The water treatments were 100 and 67% of the irrigation requirements of wheat in Toshka as normal and drought condition, respectively. A transgressive segregation in both populations for all studied traits inducted the suitability of those material for pedigree selections. The genetic advanced for grain yield/plant and its components were greater in population 2 than in population 1 in the first cycle in pedigree selection. Highly significant differences among the selected families for all the studies traits were observed in both populations under normal and drought conditions. After one cycles of selection, the broad sense heritability was very high for most traits and reached 77.79 and 92.02% for grain yield/plant under normal irrigation, while were 87.53 and 93.12% under drought stress in population 1 and population 2, respectively. Two cycles of pedigree selection for grain yield/plant was enough to detect the best families and could be performed in the early segregating generations. It could be concluded that single trait selection was efficient to improve the selection criteria in these populations. These genotypes could be sources for drought tolerance.

Assessment of agro-morphological variability of dry-season sorghum cultivars in Chad as novel sources of drought tolerance

Dry-season sorghum is a type of sorghum whose establishment ends at the end of the rainy season and its development takes place during the dry and cold harmattan period. Its root system is particularly well developed with deep penetration for water withdrawal. This study was conducted to assess the level of genetic diversity present among dry-season sorghum in Chad’s Sudanese zone using phenotypic traits, and to identify new sources of drought tolerance that could be used in sorghum breeding programs. A high variability in qualitative traits was observed except for the botanical race which showed that all cultivars were of durra race. It was also observed that most cultivars had compact panicles (66.67%), mostly black glumes (66.67%), glume hairiness (58.33%) and did not have aristation (91.67%). Most qualitative traits showed a coefficient of variation of less than 30%, and the analysis of the variance showed that at 0.1% probability, there were significant differences between cultivars for all traits except botanical race. It was observed that the potential productivity of dry-season sorghum of this collection was strongly related to their staygreen characteristic; a trait of enormous importance in breeding for postflowering drought tolerance in sorghum. Plant height was highly heritable (91.9%), followed by the peduncle length (90.2%), panicle length (87.5%) and the internodes number (86.5%). Structuring of diversity separated the cultivars into four statistically distinct groups; with group 2 clustering cultivars with panicle productivity, early maturity and high staygreen, and other traits that contribute to the performance of cultivars. The findings will help to enhance the selection and production of dry-season sorghum in Chad and also provide alternative sources for staygreen introgression into the larger sorghum breeding community.

Agronomic performances of aromatic and non-aromatic M1 rice under drought stress

Abstract Flooded rice paddy fields act as a source of greenhouse gas emissions. So, the efforts to increase the drought tolerance of rice represent a much more environmentally friendly solution, and may bring a significant contribution to prevent global warming. The experiment was laid out in a split-plot design with ten replicates. Rice cultivars treated with different levels of γ irradiation and sodium azide (SA) soaking time were allocated in the main plots, and mutagen groups in sub-plots. We use the generalized linear models, as implemented in the GLIMMIX procedure of SAS University Edition, to analyze agronomic performances. These results showed that the genotypes in M1 generation present diversity under the drought stress level of -0.03 MPa, and the best combination between cultivar and mutagen is Inpago Unsoed 1 that was irradiated with γ 100 Gy and then soaked in SA for 2h. These genotypes can be used as a sources of drought tolerance in future rice breeding programmes.

Effect of Drought Stress on Yield Performance of Parental Chickpea Genotypes in Semi-arid Tropics

Chickpea (Cicer arietinum L.) is an important cool season food legumes with indeterminate growth habit. The crop is valued for its nutritive seeds and used as animal feed in many developing countries. The productivity of the crop is constrained by several abiotic stresses, among which drought stress is one of the key determinants of crop performance aaccounting for 40-50% yield reduction globally. The present study was conducted to screen, evaluate and select chickpea genotypes possessing high yield potential under drought stress condition at ASALs (arid and semi-arid lands) of Kenya. The experiment was conducted at Chemeron dry land and Eco-tourism Research station, Egerton University and Kenya Agricultural and Livestock Research Institute (KALRO), Pekerra, Marigat, Baringo County. The genotypes were planted in RCBD (randomized complete block design) in three replicates at a spacing of 30 cm × 10 cm, giving a plant density of approximately 25 plants/m2. Combined analysis of variance revealed existence of highly significant differences among the tested genotypes for most of the agronomic traits. Overall, the highest grain yield was obtained from ICCV 92944 (1,173 kg/ha), ICCV 92318 (1,103 kg/ha) and CAVIR (975 kg/ha), ICCV 92318 (967 kg/ha), ICCV 00108 (956 kg/ha) and ICC 4958 (921 kg/ha): possibly due to its comparatively higher drought (and heat) tolerance, and hence could be used as sources of drought tolerance in further breeding programs. This study was carried out in few drought tolerant sites and further more sites need to be evaluated in addition to other drought and heat screening and optimization of protocols, facilities and analytical approaches to identify better genotypes that respond appropriately to climate change.

Diversity in root growth responses to moisture deficit in young faba bean (Vicia faba L.) plants.

BackgroundSoil moisture deficiency causes yield reduction and instability in faba bean (Vicia faba L.) production. The extent of sensitivity to drought stress varies across accessions originating from diverse moisture regimes of the world. Hence, we conducted successive greenhouse experiments in pots and rhizotrons to explore diversity in root responses to soil water deficit.MethodsA set of 89 accessions from wet and dry growing regions of the world was defined according to the Focused Identification of Germplasm Strategy and screened in a perlite-sand medium under well watered conditions in a greenhouse experiment. Stomatal conductance, canopy temperature, chlorophyll concentration, and root and shoot dry weights were recorded during the fifth week of growth. Eight accessions representing the range of responses were selected for further investigation. Starting five days after germination, they were subjected to a root phenotyping experiment using the automated phenotyping platform GROWSCREEN-Rhizo. The rhizotrons were filled with peat-soil under well watered and water limited conditions. Root architectural traits were recorded five, 12, and 19 days after the treatment (DAT) began.ResultsIn the germplasm survey, accessions from dry regions showed significantly higher values of chlorophyll concentration, shoot and root dry weights than those from wet regions. Root and shoot dry weight as well as seed weight, and chlorophyll concentration were positively correlated with each other. Accession DS70622 combined higher values of root and shoot dry weight than the rest. The experiment in GROWSCREEN-Rhizo showed large differences in root response to water deficit. The accession by treatment interactions in taproot and second order lateral root lengths were significant at 12 and 19 DAT, and the taproot length was reduced up to 57% by drought. The longest and deepest root systems under both treatment conditions were recorded by DS70622 and DS11320, and total root length of DS70622 was three times longer than that of WS99501, the shortest rooted accession. The maximum horizontal distribution of a root system and root surface coverage were positively correlated with taproot and total root lengths and root system depth. DS70622 and WS99501 combined maximum and minimum values of these traits, respectively. Thus, roots of DS70622 and DS11320, from dry regions, showed drought-avoidance characteristics whereas those of WS99501 and Mèlodie/2, from wet regions, showed the opposite.DiscussionThe combination of the germplasm survey and use of GROWSCREEN-Rhizo allowed exploring of adaptive traits and detection of root phenotypic markers for potential drought avoidance. The greater root system depth and root surface coverage, exemplified by DS70622 and DS11320, can now be tested as new sources of drought tolerance.

Drought-Tolerant Brassica rapa Shows Rapid Expression of Gene Networks for General Stress Responses and Programmed Cell Death Under Simulated Drought Stress

Production of oilseed rape/canola (Brassica napus) is increasingly threatened by dry conditions while the demand for vegetable oil is increasing. Brassica rapa is a genetically diverse ancestor of B. napus, and is readily crossed with B. napus. Recently, we reported promising levels of drought tolerance in a wild type of B. rapa which could be a source of drought tolerance for B. napus. We analysed global gene expression by messenger RNA sequencing in seedlings of the drought-tolerant and a drought-sensitive genotype of B. rapa under simulated drought stress and control conditions. A subset of stress-response genes were validated by reverse transcription quantitative PCR. Gene ontology enrichment analysis and pathway enrichment analysis revealed major differences between the two genotypes in the mode and onset of stress responses in the first 12 h of treatment. Drought-tolerant plants reacted uniquely and rapidly by upregulating genes associated with jasmonic acid and salicylic acid metabolism, as well as genes known to cause endoplasmic reticulum stress and induction of programmed cell death. Conversely, active responses in drought-sensitive plants were delayed until 8 or 12 h after stress application. The results may help to identify biomarkers for selection of breeding materials with potentially improved drought tolerance.

GENETIC CONSERVATION, CHARACTERIZATION AND UTILIZATION OF WILD RELATIVES OF FRUIT AND NUT CROPS AT THE USDA GERMPLASM REPOSITORY IN DAVIS, CALIFORNIA

The National Clonal Germplasm Repository (NCGR) in Davis is one among the nine repositories in the National Plant Germplasm System, USDA-ARS, that is responsible for conservation of clonally propagated woody perennial subtropical and temperate fruit and nut crop germplasm. Currently the repository holds over 6500 accessions of germplasm of Actinidia (kiwi fruit), Diospyros (persimmon), Ficus (fig), Juglans (walnuts), Morus (mulberry), Olea (olive), Pistacia (pistachio), Prunus (stonefruits and almond), Punica (pomegranate), Vitis (grape), and other minor genera. Wild relatives are widely represented in these collections with about 91% of the taxa and 43% of the total accessions representing the wild gene pools. Research at the repository is mainly focused on genetic characterization of germplasm using molecular markers and morphological traits to quantify and describe genetic structure and differentiation within and among species and gene pools. Promoting the use of crop wild relatives (CWR) germplasm in genetic improvement of tree fruit and nut crops is our top priority. Presently, at the Davis repository, we are extensively utilizing Prunus and Juglans wild relatives for developing improved rootstocks with resistance to biotic and abiotic stresses. We will review and discuss the results of ongoing programs highlighting the importance of different CWRs as donors of genes for resistance to major soil borne diseases such as crown gall, Phytophthora rots, and nematodes in the rootstock improvement programs. Breeding for drought tolerance is another major thrust for which we are screening CWR germplasm to identify novel sources of drought tolerance to infuse into ongoing rootstock breeding programs.

Gas Exchanges and Biological Nitrogen Fixation in Soybean under Water Restriction

Biological nitrogen fixation (BNF) in soybean is vulnerable to drought; however, there are genotypic variations among soybean cultivars regarding the ability to keep BNF under moderate water restriction. The aim of this study was to evaluate parameters related to gas exchanges and regulation of BNF in soybean genotypes BNF drought-tolerant (R01-581F and R01-416F), or drought-susceptible (CD 215 and BRS 317), submitted to adequate water supply or restriction between 45 and 55 days after emergence. We searched for traits associated with tolerance/susceptibility to drought, which might be useful in the selection of drought-tolerant soybean genotypes. Plant biomass was not affected under water restriction, but the number and dry weight of nodules reduced by 33% and 12%, respectively, in the average of genotypes. Drought-tolerant genotypes were more effective in maintaining gas exchanges under water restriction. Under water restriction, all genotypes increased the concentration of ureides in nodules, but only the susceptible genotypes showed that in leaves. The maintenance of gas exchanges and N metabolism regulation under water restriction in genotype R01-581F suggests that these parameters may be used to characterize soybean genotypes that can be sources of drought tolerance in genetic breeding programs.

Estimation of drought tolerance among maize landraces from mini-core collection

Global climate change, its impact on stable food production in the future and possibilities to overcome the problem are the major priorities for research. Breeding varieties with increase adaptability to changing environments, together with better tolerance/resistance to abiotic stress, pest and diseases are possible solution. Maize is one of the most important crops, with high grain yield reduction induced by drought stress. In the present study twenty-six maize landraces from drought tolerant mini-core collection were tested under optimal, drought, and a combination of drought and high density stresses in the field. Morphological traits, plant height, total number of leaves, leaf length, leaf width, anthesis-silking interval and grain yield were recorded for each entry in two replications in three experiments. Besides, drought tolerant indices were evaluated to test the ability to separate more drought tolerant accessions from those with less stress tolerance. Five stress tolerance indices, including stress tolerance index (STI), mean productivity (MP), geometric mean productivity (GMP), stress susceptibility (SSI), and stress tolerance (TOL) were calculated. Data analyses revealed that STI, MP and GMP had positive and significant correlations with grain yield under all conditions. Three-dimensional diagrams displayed assignment of landraces L25, L1, L14, L3, L26, L15 and L16 to group A, based on the stress tolerance index and achieved grain yield under optimal, drought stress, and a combination of drought and high density stress. A biplot analysis efficiently separated groups of landraces with different level of drought tolerance and grain yield. Based on all obtained results, maize landraces L25, L14, L1 and L3, as the most valuable source of drought tolerance, could be recommended for further use in breeding programs.

SSR analysis of introgression of drought tolerance from the genome of Hordeum spontaneum into cultivated barley (Hordeum vulgare ssp vulgare)

Wild barley (Hordeum vulgare ssp. spontaneum) and landraces are important sources of resistance to biotic and abiotic stresses since they possess wide genetic diversity that may be missing in current elite varieties. In this study, we evaluated a set of 57 barley introgression lines divided in groups depending on the expected levels of introgression (50, 25, and 12.5 %) from one Hordeum spontaneum accessions (Hsp 41-1) and on those (50 and 25 %) from a second (Hsp 41-5); in both cases the 25 % level was represented by two groups depending on the other parent. The two H. spontaneum accessions have been used as the best sources of drought tolerance in the ICARDA barley-breeding program. Graphical genotyping and genetic diversity analysis were used to examine the relative contribution of H. spontaneum and the extent of genetic differences among the 57 lines using 74 microsatellite markers that cover 941 cM of the barley genome. The average proportion of the genome containing H. spontaneum alleles in each group was of 44.5 %, group 1; 24.6 %, group 2; 21.6 %, group 3; 45.4 %, group 4; 19 %, group 5; 15.5 %, group 6 and 11.4 %, group 7. Introgression lines in group 1 and 4, with the highest observed introgression with Hsp 41-1 and Hsp 41-5, showed higher grain yield and better agronomic performance under field conditions in Breda and Khanaser, i.e., the two most stressed environments in which the groups were phenotyped, indicating the usefulness of using H. spontaneum as a source of chromosomal linkage blocks important for improved drought tolerance. However, more extensive genome coverage will be needed to identify the specific chromosomal regions associated with superior performance under extreme drought.

Genetic analysis and phenotypic associations for drought tolerance in Hordeum spontaneum introgression lines using SSR and SNP markers

Associations between markers and drought related traits were investigated on a set of 57 advanced barley breeding lines, carrying various levels of introgression from Hordeum spontaneum lines 41-1 and 41-5, the best sources of drought tolerance in the ICARDA barley breeding program, using 74 simple sequences repeats (SSR) and 20 single nucleotide polymorphism markers. The 57 lines were evaluated for grain yield and drought related traits for three years (2003/04, 2004/05, 2005/06) in nine Mediterranean low rainfall environments. A high level of polymorphism was found with SSR markers, and the mean polymorphism information content and gene diversity values were 0.67 and 0.71, respectively. The number of alleles per locus varied from 2 to 11, with an average of 5.8 alleles per marker. Considering all the 57 lines, the linkage disequilibrium (LD) analysis was significant at a comparison-wise P < 0.01 level in nearly 9 % of the SSR marker pairs used and a decay of LD was observed to a value of r2 < 0.2 at a genetic distance of 40 cM. The association analysis revealed a total of 147 significant marker–trait associations for grain yield and drought related traits. A total of 72 (49 %) marker–trait associations showed favorable effects of the exotic germplasm where the H. spontaneum lines contributed to an improvement of the trait under drought stress conditions. The number of significant marker–trait associations per trait were: 12 for growth habit; 2 for growth vigor; 11 for peduncle extrusion; 5 for number of grains per spike; 20 for peduncle length; 16 for days to heading; 20 for plant height; 8 for spike length; 17 for thousand kernel weight; 30 for grain yield; 4 for harvest index and 2 for biological yield. The phenotypic variation explained by individual marker–trait associations ranged from 7.6 % to 36.2 %. The identification of genomic regions associated with grain yield and drought related traits is useful for the genetic improvement of cultivars better adapted to drought stress environments. Thus, the present study is encouraging in identifying significant marker–trait associations through LD based association mapping analysis, which could complement and augment previous quantitative trait loci information for the potential use of Marker Assisted Selection for drought.

Development of a Mesoamerican intra-genepool genetic map for quantitative trait loci detection in a drought tolerant × susceptible common bean (Phaseolus vulgaris L.) cross

Drought is a major constraint to common bean (Phaseolus vulgaris L.) production, especially in developing countries where irrigation for the crop is infrequent. The Mesoamerican genepool is the most widely grown subdivision of common beans that include small red, small cream and black seeded varieties. The objective of this study was to develop a reliable genetic map for a Mesoamerican × Mesoamerican drought tolerant × susceptible cross and to use this map to analyze the inheritance of yield traits under drought and fully irrigated conditions over 3 years of experiments. The source of drought tolerance used in the cross was the cream-seeded advanced line BAT477 crossed with the small red variety DOR364 and the population was made up of recombinant inbred lines in the F5 generation. Quantitative trait loci were detected by composite interval mapping for the traits of overall seed yield, yield per day, 100 seed weight, days to flowering and days to maturity for each field environment consisting of two treatments (irrigated and rainfed) and lattice design experiments with three repetitions for a total of six environments. The genetic map based on amplified fragment length polymorphism and random amplified polymorphic DNA markers was anchored with 60 simple sequence repeat (SSR) markers and had a total map length of 1,087.5 cM across 11 linkage groups covering the whole common bean genome with saturation of one marker every 5.9 cM. Gaps for the genetic map existed on linkage groups b03, b09 and b11 but overall there were only nine gaps larger than 15 cM. All traits were inherited quantitatively, with the greatest number for seed weight followed by yield per day, yield per se, days to flowering and days to maturity. The relevance of these results for breeding common beans is discussed in particular in the light of crop improvement for drought tolerance in the Mesoamerican genepool.