Common beans (Phaseolus vulgaris L.) originated in the New World and are the grain legume of greatest production for direct human consumption. Common bean production is subject to frequent droughts in highland Mexico, in the Pacific coast of Central America, in northeast Brazil, and in eastern and southern Africa from Ethiopia to South Africa. This article reviews efforts to improve common bean for drought tolerance, referring to genetic diversity for drought response, the physiology of drought tolerance mechanisms, and breeding strategies. Different races of common bean respond differently to drought, with race Durango of highland Mexico being a major source of genes. Sister species of P. vulgaris likewise have unique traits, especially P. acutifolius which is well adapted to dryland conditions. Diverse sources of tolerance may have different mechanisms of plant response, implying the need for different methods of phenotyping to recognize the relevant traits. Practical considerations of field management are discussed including: trial planning; water management; and field preparation.

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Phenotyping common beans for adaptation to drought.

Legumes are well recognized for their nutritional and health benefits as well as for their impact in the sustainability of agricultural systems. The threatening scenario imposed by climate change highlights the need for concerted research approaches in order to develop crops that are able to cope with environmental stresses, while increasing yield and quality. During the last decade, some physiological components and molecular players underlying abiotic stress responses of a broad range of legume species have been elucidated. Plant physiology approaches provided general outlines of plant responses, identifying stress tolerance-related traits or elite cultivars. A thorough identification of candidate genes and quantitative trait loci (QTLs) associated with these traits followed. Model legumes like Medicago truncatula, Lotus japonicus, and more recently, Glycine max provided valuable translational approaches for dissecting legume responses to abiotic stresses. The challenge now focuses on the translation of...

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Abiotic Stress Responses in Legumes: Strategies Used to Cope with Environmental Challenges

Drought stress is the major limitation of common bean (Phaseolus vulgaris L.) grown in subsistence farming systems worldwide. The objective of this study was to use single nucleotide polymorphism (SNP) markers from the BARCBean6K_3 Beadchip to identify quantitative trait loci (QTL) associated with traits related to drought tolerance in common bean. An intergene pool recombinant inbred line (RIL) population from a cross of drought tolerant line SEA5 and CAL96 cultivar was evaluated in Rwanda for 3 yr under drought stress and nonstress and in Colombia for 1 yr under drought stress. Traits evaluated included the numbers of days to flower, maturity, and seed fill; harvest index and pod harvest index; yield and yield components including number of pods per plant, seeds per pod, 100 seed weight (SW), and seed yield per day. Harvest indices, and SW were stable regardless of water treatment while number of pods per plant, seeds per pod, and yield were significantly reduced by drought. A linkage map of the RIL population spanning 1351 cM was constructed using 2122 SNP markers. The map covered all eleven bean chromosomes with an average distance of 0.64 cM between markers. A total of 14 QTL for performance under drought were consistently identified in different environments. Quantitative trait loci associated with phenology and SW traits mapped near previously reported QTL. Linkage between SW and yield QTL SY3.3SC was observed on Pv03 and could be used to simultaneously select for seed yield and size in intergene pool crosses of common bean.

Quantitative Trait Loci Associated with Drought Tolerance in Common Bean

Common bean (Phaseolus vulgaris L.) is the most important food legume in the diet of poor people in the tropics. Drought causes severe yield loss in this crop. Identification of traits associated with drought resistance contributes to improving the process of generating bean genotypes adapted to these conditions. Field studies were conducted at the International Center for Tropical Agriculture (CIAT), Palmira, Colombia, to determine the relationship between grain yield and different parameters such as effective use of water (EUW), canopy biomass, and dry partitioning indices (pod partitioning index, harvest index, and pod harvest index) in elite lines selected for drought resistance over the past decade. Carbon isotope discrimination (CID) was used for estimation of water use efficiency (WUE). The main objectives were: (i) to identify specific morpho-physiological traits that contribute to improved resistance to drought in lines developed over several cycles of breeding and that could be useful as selection criteria in breeding; and (ii) to identify genotypes with desirable traits that could serve as parents in the corresponding breeding programs. A set of 36 bean genotypes belonging to the Middle American gene pool were evaluated under field conditions with two levels of water supply (irrigated and drought) over two seasons. Eight bean lines (NCB 280, NCB 226, SEN 56, SCR 2, SCR 16, SMC 141, RCB 593, and BFS 67) were identified as resistant to drought stress. Resistance to terminal drought stress was positively associated with EUW combined with increased dry matter partitioned to pod and seed production and negatively associated with days to flowering and days to physiological maturity. Differences in genotypic response were observed between grain CID and grain yield under irrigated and drought stress. Based on phenotypic differences in CID, leaf stomatal conductance, canopy biomass, and grain yield under drought stress, the lines tested were classified into two groups, water savers and water spenders. Pod harvest index could be a useful selection criterion in breeding programs to select for drought resistance in common bean.

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Effective Use of Water and Increased Dry Matter Partitioned to Grain Contribute to Yield of Common Bean Improved for Drought Resistance

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 studies were conducted over two seasons at Centro Internacional de Agricultura Tropical (CIAT), Palmira, Colombia to (i) evaluate phenotypic differences in drought resistance; and (ii) identify adaptive traits that can be used in on-going breeding programmes of common bean for developing drought resistant genotypes. A total of 36 genotypes, including elite inbred and interspecific lines and landraces of common bean and tepary bean were evaluated under field conditions with two levels of water supply (irrigated and rainfed). Results showed that two accessions of tepary bean, P. acutifolius (G 40159 and G 40068) and two elite lines (RAB 650, SEA 23) of common bean were outstanding in their adaptation to terminal drought stress. The superior performance of these genotypes under drought stress was associated with their ability to mobilise photosynthates from leaves and stems to developing grain. Tepary bean was superior to common bean in combinig several desirable traits that contribute to greater level of adaptation to terminal drought stress. Canopy biomass, pod partitioning index, stem biomass reduction and pod harvest index could serve as useful traits to improve the efficiency of breeding programmes to select superior genotypes of common bean under terminal drought stress. Keywords: Abiotic stress, harvest index, water stress African Crop Science Journal , Vol. 21, No. 4, pp. 265 - 281

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Can tepary bean be a model for improvement of drought resistance in common bean

Interspecific lines obtained from crosses between common bean (Phaseolus vulgaris L.) and other species from its secondary gene pool have a tendency for excessive vegetative growth and low grain yield. Contrariwise, drought-adapted common bean lines have been observed to produce high yields despite low shoot biomass production. This was attributed to greater remobilization of photosynthates to grain development. The objective of the present study was to investigate whether F2-families derived from crosses between an interspecific line and drought-adapted P. vulgaris lines have improved ability to remobilize greater proportion of photosynthate from shoot biomass to grain yield and subsequently obtain higher yield potential. Seven F2-progenies derived from crosses of an interspecific hybrid line of P. vulgaris × Phaseolus dumosus with seven drought-adapted lines reflecting a range of photosynthate remobilization and partitioning were evaluated under irrigated and rainfed field conditions along with their eight parent lines and one drought-tolerant check at the International Center of Tropical Agriculture (CIAT) at Palmira, Colombia. Although no single parent trait led to higher yield potential in progenies, the mean yield potential of the progenies, as well as mean yield under drought was significantly higher than yields of the interspecific parent, indicating that crosses with drought-adapted bean lines with greater plant efficiency constitute a promising breeding approach for yield improvement of interspecific crosses in both drought stressed and favorable environments.

https://www.academicjournals.org/article/article1380030288_Klaedtke et al.pdf

Photosynthate remobilization capacity from drought-adapted common bean (Phaseolus vulgaris L.) lines can improve yield potential of interspecific populations within the secondary gene pool

Common bean is an important staple crop in the tropics of Africa, Asia and the Americas. Particularly smallholder farmers rely on bean as a source for calories, protein and micronutrients. Drought is a major production constraint for common bean, a situation that will be aggravated with current climate change scenarios. In this context, new tools designed to understand the genetic basis governing the phenotypic responses to abiotic stress are required to improve transfer of desirable traits into cultivated beans. A multiparent advanced generation intercross (MAGIC) population of common bean was generated from eight Mesoamerican breeding lines representing the phenotypic and genotypic diversity of the CIAT Mesoamerican breeding program. This population was assessed under drought conditions in two field trials for yield, 100 seed weight, iron and zinc accumulation, phenology and pod harvest index. Transgressive segregation was observed for most of these traits. Yield was positively correlated with yield components and pod harvest index (PHI), and negative correlations were found with phenology traits and micromineral contents. Founder haplotypes in the population were identified using Genotyping by Sequencing (GBS). No major population structure was observed in the population. Whole Genome Sequencing (WGS) data from the founder lines was used to impute genotyping data for GWAS. Genetic mapping was carried out with two methods, using association mapping with GWAS, and linkage mapping with haplotype-based interval screening. Thirteen high confidence QTL were identified using both methods and several QTL hotspots were found controlling multiple traits. A major QTL hotspot located on chromosome Pv01 for phenology traits and yield was identified. Further hotspots affecting several traits were observed on chromosomes Pv03 and Pv08. A major QTL for seed Fe content was contributed by MIB778, the founder line with highest micromineral accumulation. Based on imputed WGS data, candidate genes are reported for the identified major QTL, and sequence changes were identified that could cause the phenotypic variation. This work demonstrates the importance of this common bean MAGIC population for genetic mapping of agronomic traits, to identify trait associations for molecular breeding tool design and as a new genetic resource for the bean research community.

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Alberto Guerrero

Papers

Photosynthate remobilization capacity from drought-adapted common bean (Phaseolus vulgaris L.) lines can improve yield potential of interspecific populations within the secondary gene pool

Genetic mapping for agronomic traits in a MAGIC population of common bean ( Phaseolus vulgaris L.) under drought conditions

Replication Data for: Genetic mapping for agronomic traits in a MAGIC population of common bean (Phaseolus vulgaris L.) under drought conditions