Study of genetic parameters and relationships between agronomic and physiological traits in Kabuli type chickpea genotypes under drought stress

Chickpea is one of the most important protein producing crops in the world and drought is the greatest limiting factor for its growth. In addition, chickpea plays crucial role in soil fertility because of the nitrogen fixation in its roots. The chickpea is mostly grown in semi-arid and arid zones or in the rain fed condition. Hence, more than 90% of chickpea growing area is drought prone. Under such conditions, usually the last part of reproductive phase of chickpea, faces water deficiency. Generally terminal drought stress is responsible for reduction in yield and biomass as well as physiological traits such as CO2 assimilation, stomatal conductance, transpiration rate, membrane stability index (MSI) and water use efficiency (WUE). In this condition, stress avoidance ability, tolerance or stress escape is essential for drought resistance. Significant genetic variation exists in chickpea germplasms for terminal drought stress. Nowadays, different breeding methods used for improving chickpea drought tolerance such as Marker assisted selection, omics and mutation breeding. Besides these techniques, enough information about traits affected by drought stress, their genetic parameters and relationships with economic yield is necessary for breeding programs.
 

According to estimation of genetic variation, heritability and relationships between agronomic, morphological and physiological traits, 64 Kabuli type chickpea genotypes were sown under two normal and terminal drought conditions in two-separated 8×8 lattice design in Shahid Bahonar University of Kerman during 2015-2016 growing season. Normal irrigation applied until flowering stage. Water withdrawing was done at 50% of flowering stage. Agronomic traits such as days to secondary branch, days to flowering, days to maturity, plant height, leaflet numbers, seed yield, yield components, harvest index, seed filling period, seed filling rate measured. Chlorophyll content measured by the SPAD chlorophyll meter. Stomatal conductance and net photosynthesis were measured by CI-340 Handheld Photosynthesis System apparatus from Bio-Science Company. Data was analyzed by SPSS ver. 22. Estimation of genetic parameters and path analysis were performed for all significant traits in both normal and terminal drought stress.
 

Analysis of variance for genotypes determined significant differences for day to secondary branch, day to flowering, day to pod setting, 100 seed weight and seed filling period in normal condition. Genotypes showed significant difference for all traits except number of seeds per pod, biological yield, seed filling rate and the SPAD index in stress condition. According to the results of genetic parameter estimation for normal condition the highest amount of CVg was belonged to seed filling period, leaflet number and 100 seed weight, which were 11.1, 9.13 and 8.4, respectively. The highest amount of heritability in normal condition also was belonged to days to flowering and days to secondary branch, which were 68.47 and 68.44, respectively. The highest amount of CVg obtained in terminal drought condition for stomatal conductance and net photosynthesis, were 33.14 and 31.76 respectively. Stomatal limitation and reduction in photosynthesis are the most important factors for loss of yield during stress condition. Therefore, the usage of mentioned genetic diversity may improve future breeding program for drought condition. However, marker assisted selection methods might be helpful, according to moderate heritability of these traits (29.58 and 24.08, respectively). Result of path analysis in normal condition determined that seed-filing period had the most magnitude direct effect (0.527) and the large indirect effect (0.365) via number of seeds per plant on seed yield. The highest amount of direct effect (0.702) on seed yield belonged to rate of filling in drought condition as well. It seems that during terminal progressive drought stress, the ability of filling the seed rapidly is the key trait for tolerant genotypes according to limitation in the seeds filling period.
 

Terminal drought stress is one of two reasonable factors reducing chickpea yield. The result of analysis of variance for genotypes indicated significant differences for days to secondary branch, days to flowering, days to pod setting, 100 seed weight and seed filling period in normal condition. In addition to mentioned traits, significant difference was achieved for days to maturity, seed yield, and number of pods per plant, harvest index, net photosynthesis and stomatal conductance. The highest amount of CVg belonged to seed filling period, leaflet number and 100 seed weight. However, highest CVg belonged to stomatal conductance and net photosynthesis in drought stress condition. In practice, relatively high genetic variation for these traits might be a new insight for improving drought tolerance in chickpea. The high direct and indirect effects of seed filling rate on seed yield in path analysis suggested a strong relationship between these characters. Moreover, the magnitudes of both direct and indirect effect of seed filling rate via number of seed per plant were increased during stress condition. According to the results, some physiological traits such as stomatal conductance, net photosynthesis and seed filling rate might be valuable in future breeding programs.