Evaluation of traits and drought tolerance in common bean (Phaseolus vulgaris L.) genotypes under well-watered and drought stress conditions

IntroductionPulse crops with 18-32% protein are the most important source of grain for human food. Protein of food legumes due to the presence of essential amino acids such as Lysine, have high nutritional value. Common beans are half of the beans used in the world, its grains rich in protein and carbohydrates. Common bean is very sensitive to weather conditions and soil quality and its performance even in short periods of stress. About two-thirds of the land under cultivation in Iran is in semi-arid areas, so the varieties with resistance to drought stress are the most important objectives of the breeding programs. Genetic diversity is the base for the selection of genotypes with desirable traits. In addition genetic resources have the fundamental role for agricultural development, as a source of useful genes for resistance to biotic and abiotic stresses and the development of genetic adaptation to environmental changes considered that the proper utilization of these varieties can be produced new and more desirable plants.
Materials & MethodsIn order to evaluate genotypic and phenotypic variation and determine the relationship between grain yield with other traits in 35 common bean genotypes under normal and drought stress conditions, an experimental design was carried out in a randomized complete block design under two conditions in 2013 at the research field of college of Agriculture and natural resource of University of Tehran in Karaj state with latitude 35° and 56 minutes north and longitude 50° and 58 minutes east and 1112.5 m height above sea level. Treatments consisted of 33 common bean genotypes with three Khomein, Daneshkadeh and Goli Cultivars as control, were selected from the collections of College of Agriculture, University of Tehran, Karaj. Based on 30 years of data, mean annual precipitation of 243 mm and the test run of 47.7 mm rainfall during the growing season was over. Planting was done manually. Each plot consisted of three rows of two meters in length and with a spacing of 50 cm and 10 cm seeds space on the row and depth of planting was about five centimeters. Irrigation took place similar to both conditions at flowering stage, for seven days (Equivalent to 70 mm evaporation) and after the vegetative growth and loss of the risk sufficient to remove the bushes. Irrigation of water stress piece was performed each 11 days (Equivalent to 110 mm evaporation). Harvest was performed when 90% of plants were matured and the seven plants in compliance with marginal effect of each plot were collected to measure traits and then by using the mean yield genotypes per plot in non-stress (Ypi) and stress conditions (Ysi), drought tolerance indices including, Mean Productivity, Geometric Mean Productivity, Harmonic Mean Productivity, Stress Tolerance Index, Stress Susceptibility Index, Tolerance Index, Yield Index, Yield Stability Index, Stress Intensity and yield reduction rate were calculated for each genotype.
Results & DiscussionResults showed that among genotypes in the studied traits there were significant differences which displayed genetic variation among the genotypes. Based on the average of genotypes yield in normal conditions the highest and lowest seed yield pertained genotypes 27 and 12, respectively, and in the stress related to genotypes 32 and 12, respectively. According to the results of phenotypic correlations, stepwise regression, and path analysis in both normal and stress conditions, the traits of seed and pod weight, biological yield, number of seeds per plant, and number of seed per pod were the most important and effective traits affecting yield. The highest diversity was observed for these traits; therefore the selection of these traits can ideally improve the yield. Based on factor analysis, five factors were selected that the total variation were explained 83.76 and 80.79 percent under normal and drought stress conditions, respectively. The first and second factors were named yield and yield component factors. Geometric Mean Productivity, Harmonic Mean and Stress Tolerance Index, indices had the highest significant correlation with yield in both conditions, hence, were introduced as the best indices for screening tolerant genotypes. Based on biplot graph, genotypes 25, 27 and 28 were identified as tolerant genotypes with high yield, whereas genotypes 7, 10, 22 and 23 as drought-sensitive genotypes. Based on indicators STI, GMP, GMP, HRM and performance in normal and stress conditions, using Ward method genotypes were classified in three clusters 21 genotypes in first class, 3 genotypes in cluster II and 11 genotypes were in Cluster III and tolerant genotypes with the highest distance from sensitive genotypes (cluster I) in the third cluster.
ConclusionThus, according to genetic distance can be genotypes in breeding programs to produce hybrids with high yield and drought tolerance can be used.