Investigation of photosynthetic and yield traits and the relationship between them in lentil genotypes under rainfed conditions

Considering the development of cultivation and production of legumes and the importance of genetic studies in plant breeding, identifying the genetic potential of these plants is very important. Knowledge of genetic diversity and relationships between genotypes is important for understanding available genetic variability and the potential to use it in breeding programs. According to previous studies on lentils, it was found that improving the yield potential per unit area can be one of the important criteria for increasing the production of this plant. Increasing the yield per unit area is possible mainly by modifying and creating high-yielding cultivars, improving the characteristics and increasing the quantitative and qualitative potentials. Breeders and plant physiologists believe that in order to be more productive in improving compatible cultivars in areas with limited water resources, recognizing the agronomic traits affecting grain yield under stress conditions will be of great importance; Therefore, indirect selection based on physiological traits has been proposed as a complement to the selection of cultivars with high yield potential. Considering the different reactions of photosynthetic indices under stress conditions, it is important to know the genotypic diversity of photosynthetic indices under culture conditions and their relationship with grain yield. Despite numerous studies on the role of physiological traits in drought tolerance in crops, recent studies on lentils, especially in Iran, are limited. This study was designed and carried out with the aim of determining genotypes with desirable physiological and yield traits and the relationship between these traits and photosynthesis under rainfed conditions.

In order to study the photosynthetic and yield parameters of lentil plant in rainfed conditions, selected advanced lentil lines with control cultivars were studied in a randomized complete block design with 3 replications in Khodabandeh dryland research station in Zanjan Province in two cropping seasons 2018 to 2020. Physiological traits included photosynthesis per unit leaf area, stomatal conductance, transpiration rate, photosynthetic activated radiation, sub stumatal CO2, leaf temperature, photosynthetic water use efficiency, mesophilic conductivity and water use efficiency. Plant height, 100-seed weight, number of pods and yield (kg/ha) were also measured for each genotype in each plot. Analysis of variance and comparison of means were performed using Duncan's test at 5% probability level. Finally, correlation analysis and stepwise regression analysis were performed with the variables of photosynthesis rate and total yield.

The results showed that there was a significant difference in photosynthetic active radiation, leaf temperature, photosynthetic water use efficiency, mesophilic conductivity, water use efficiency, 100-grain weight and yield between two years of experiment. The studied genotypes showed significant differences in leaf temperature, photosynthesis, plant height, 100-seed weight and yield, which indicated the high genetic diversity of these genotypes in terms of these traits. The interaction effect of genotype per year was not significant in all studied traits, which shows that the trend of changes in these traits between genotypes during the two years was the same. Among the studied genotypes, G5 genotype is a genotype with superior agronomic characteristics that can be recommended as a cultivar with high yield potential. Photosynthesis rate showed a significant negative correlation with leaf temperature and significant positive correlation with transpiration rate, stomatal conductance, mesophilic conductivity, water use efficiency and 100-grain weight. 100-seed weight showed a significant negative correlation with leaf temperature and a significant positive correlation with stomatal conductance, photosynthesis, mesophilic conductivity and water use efficiency. These results show that drought and lack of water in the soil have the greatest effect on reducing photosynthesis and plant yield at different phenological stages (seedling, flowering and podding) of the plant. Finally, regression analysis showed that stomatal conductance and sub stumatal CO2 explained the changes in photosynthesis.

The results showed that for lentils, two traits of stomatal conductance and sub stumatal CO2 concentration may explain the changes in photosynthesis. Genetic diversity is very important for crop breeding and higher diversity of genotypes provides a better chance of producing a variety of desirable cultivars. The observed genetic diversity in traits can help select superior genotypes based on phenotypic expression and can be used in breeding programs to improve economically important traits. Finally, among the studied genotypes, G5 genotype was found to be a genotype with superior agronomic characteristics that could be recommended to the farmers to improve lentil yield.