Show simple item record Physiological traits associated with drought resistance in Andean and Mesoamerican genotypes of common bean (Phaseolus vulgaris L.) dc.contributor.author Polania, Jose Arnulfo dc.contributor.author Rao, Idupulapati M.

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Drought is the major abiotic stress factor limiting yield of common bean (Phaseolus vulgaris L.) in smallholder systems in Latin America and eastern and southern Africa; where it is a main source of protein in the daily diet. Identification of shoot and root traits associated with drought resistance contributes to improving the process of designing bean genotypes adapted to drought. Field and greenhouse studies were conducted at the International Center for Tropical Agriculture (CIAT), Palmira, Colombia to determine the relationship between grain yield and different shoot and root traits using a recombinant inbred lines (RILs) population (MD23–24 × SEA 5) of common bean. The main objectives of this study were to identify: (i) specific shoot and root morpho-physiological traits that contribute to improved resistance to drought and that could be useful as selection criteria in breeding beans for drought resistance; and (ii) superior genotypes with desirable shoot and root traits that could serve as parents in breeding programs that are aimed at improving drought resistance. A set of 121 bean genotypes (111 RILs, 2 parents, 8 checks) belonging to the Mesoamerican gene pool and one cowpea variety were evaluated under field conditions with two levels of water supply (irrigated and rainfed) over three seasons. To complement field studies, a greenhouse study was conducted using plastic cylinders with soil inserted into PVC pipes, to determine the relationship between grain yield obtained under field conditions with different root traits measured under greenhouse conditions. Resistance to drought stress was positively associated with a deeper and vigorous root system, better shoot growth, and superior mobilization of photosynthates to pod and seed production. The drought resistant lines differed in their root characteristics, some of them with a vigorous and deeper root system while others with a moderate to shallow root system. Among the shoot traits measured, pod harvest index, and seed number per area could serve as useful selection criteria for assessing sink strength and for genetic improvement of drought resistance in common bean.

The progress in identification of genotypes with roots showing greater ability to penetrate compacted soils under moisture stress and understanding the physiological basis and morphological expression of the characteristics associated is fundamental to improving crop's tolerance to drought and to increase productivity under individual and combined stress conditions. Our objectives were to: (i) determine genotypic differences in root penetration ability of common bean (Phaseolus vulgaris L.) using two methods (compacted soil layers and wax-petrolatum layers) to simulate soil compaction; and (ii) identify the morpho-physiological characteristics associated with the ability to penetrate compacted layers under well-watered and intermittent drought conditions in a greenhouse environment. Six common bean genotypes of different origin (Andean, Mesoamerican and interspecific) were tested in two trials. In the first trial, we evaluated genotypic differences in morpho-physiological characteristics that were associated with the root's ability to penetrate compacted soil layers of 1.2, 1.4, and 1.6 g cm −3 bulk densities. In the second trial, we used another method to determine genotypic differences in root's ability to penetrate wax-petrolatum layers of low, medium, and high mechanical impedance. The conditions for root growth were severely restricted by compaction and aggravated by drought stress. The medium level of mechanical impedance of wax petrolatum layer method showed the best results to evaluate bean genotypes for soil compaction tolerance. Among the six genotypes tested, ALB 91 (an interspecific line) was identified as the one with the greatest root penetration ability compared with A774 which showed the lowest root penetration ability under both well-watered and drought conditions.

Tepary bean (Phaseolus acutifolius A. Gray) is more heat and drought tolerant than common bean (P. vulgaris L.). Four hundred mutant lines of two tepary accessions (G40068 and G40159) were generated by ethyl methane sulfonate (EMS) treatment. In preliminary studies of the M5 mutant lines under abiotic stress, three mutant lines (CMT 38, CMT 109, CMT 187) were selected from six mutated lines based on morpho-physiological traits and superior yield and advanced to the M6 generation. The M6 mutant lines were uniform and genetically stable. These mutant lines and their original (M0) parents were evaluated for heat and drought tolerance under greenhouse conditions. Their performance was evaluated for morpho-physiological attributes, seed yield and yield components. Under high temperature and drought conditions, the CMT 38 mutant (M6 line) and its original tepary (M0) accession (G40068) showed greater values of pod biomass, pod number and 100-seed biomass than the other lines tested. The CMT 109 and CMT 187 mutant lines and their G40159 original accession (M0) also showed the highest value of seed number under high temperature and drought conditions. This suggests that the previous screening performed during the population advancement of these mutant lines, based on morphological traits like growth habit, was not detrimental to the yield variables evaluated here. Under combined heat and drought conditions, different parameters could be incorporated into tepary breeding programmes, as selection criteria to screen genotypes for tolerance to heat and drought stress. These parameters included: chlorophyll (SPAD) readings, seed biomass, 100-seed biomass and seed number because they explain the observed variance in the principal component analysis. Two additional traits (root biomass and stem diameter) were also identified as useful attributes, based on univariate analysis. The mutant lines evaluated here offer potential for further improvement of tepary bean to high temperature and drought

Heat stress is a major limitation to grain yield in common bean (Phaseolus vulgaris L.). Tepary bean (Phaseolus acutifolius A. Gray) is better adapted to heat stress than common bean. Ten tepary bean accessions, four common bean genotypes and four interspecific lines involving P. vulgaris and P. acutufolius, P. coccineus and P. dumosus were evaluated for tolerance to heat stress conditions induced under greenhouse conditions and these were compared to plants grown under ambient temperatures. The high temperature treatment was 29 ±5 °C during the day and was >24 °C (up to 27 °C) during the night, while the ambient temperature (AT) treatment was 25 ±5 °C during the day and 19± 2 °C at night. The genotypic differences were evaluated for morpho-physiological characteristics of shoot and root and also yield components. The Genotype and Genotype × Temperature interactions were significant for all shoot and root morpho-physiological characteristics evaluated. Higher temperature (HT) significantly affected leaf photosynthetic efficiency, total chlorophyll content, and stomatal conductance. The effect was positive or negative, depending on the genotypes. Tepary accessions showed reduced total chlorophyll content, while common bean genotypes and the interspecific lines were less affected. Tepary accessions also showed reduced stomatal conductance, but increased leaf photosynthetic efficiency under HT. Common bean genotypes increased stomatal conductance and decreased leaf photosynthetic efficiency. High temperature decreased total root length, specific root length and pod biomass compared to ambient conditions, but there was no marked effect on pollen viability of the tested genotypes. The superior adaptation of tepary germplasm accessions to high temperature is attributed to their ability to regulate stomatal opening and photosynthetic efficiency, together with a superior ability to remobilize photosynthates from older leaves to pods during physiological maturity

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