Relationships between some agronomic traits related to yield in Chickpea genotypes (Cicer arietinum L.) under Aschochyta blight stress conditions

Chickpea (Cicer arietinum) is an edible legume grown widely for its nutritious seed, which is rich in protein, minerals, vitamins, and dietary fiber and is the third most important food legume of the world after common bean and pea. Ascochyta blight, caused by Ascochyta rabiei, is one of the most important diseases of chickpea that limits its cultivation and production in most parts of the world, including Iran. The use of resistant cultivars is the most effective and economical strategy for management of Ascochyta blight. Therefore, identifying the genetic resources of resistance in chickpea germplasms against Ascochyta blight is very important in designing breeding programs. Furthermore genetic diversity in chickpea collection can be used in breeding program for selection of genotype with desirable agronomic traits. Studying relationships between agronomic traits under disease stress conditions would assist breeders to identify the effective traits and use proper selection intensity in their breeding programs. 

In order to assess the resistance to Ascochyta blight, and the relationship of some yield related traits and relative resistance to Ascochyta blight disease, research was conducted with 77 advanced chickpea genotypes received from ICARDA in a randomized complete block design with three replications at the Agricultural Research Station of Gonbad-e-Kavous in 2017. Plants were inoculated by applying uniformly scattered infected chickpea debris after seedling emergence. The degree of susceptibility and resistance to disease of each line was determined using 1-9 rating scale and area under disease progress curve was also calculated. Various phonological and morphological traits including yield and yield components were measured. 

According to the results of ANOVA, there was a significant difference among genotypes for all traits (p< 0.01) which revealed genetic variation among them. Genotype of 76 and 55 with an average of 118.67 and 14.81 kilograms grain per hectare had the highest and lowest yield, respectively. The results of phenotypic correlation under disease-stress condition showed that plant height had the highest correlation (-0.586, p< 0.01) with Ascochyta blight progress. AUDPC was also correlated to grain yield negatively. Genotypes 13, 27, 29, and 34 which belong to the most sensitive group to the disease, had the lowest grain yield and the resistant genotype of 34, had the highest grain yield. AUDPC had also negative correlation (p< 0.01) with plant height and height of the first pod from ground. There was a positive correlation at 1% probability level between AUDPC and days to 50% flowering and days to physiological maturity revealed that as the disease progresses, those two factors become longer. Genotypes 34 and 35 which had the longest days to physiological maturity were belonging to disease sensitive group. Stepwise regression analysis introduced AUDPC, number of two seed pods and plant height with 42% justify changes as the most effective traits. According to the results of stepwise regression, plant height had the highest effect on grain yield. The results of Path analysis showed that plant height had the most direct effect on grain yield (0.357) and the most indirect effect was related to AUDPC via plant height (-0.1151). Therefore, plant height can be used as a superior trait in indirect selection programs. Based on agronomic traits under disease stress conditions, cluster analysis set the genotypes into two groups using the square Euclidian distance and Ward method. The genotypes of first cluster, had the highest average in plant height, height of the first pod from ground, number of two seed pods, grain yield and 100-grain weight compared to the other one. The second group was earliness and had higher days to 50% flowering, days to physiological maturity and grain filling period. According to the results of cluster analysis for disease parameter based on the square Euclidian distance and Ward method, the genotypes classified in three clusters including tolerant, sensitive, and resistant where 25, 37, and 15 genotypes were placed in resistant, tolerant, and susceptible groups, respectively. The sensitive group had less grain yield than the others. Genotype 26 was highly susceptible and genotypes 6, 22, 43 and 65 were identified as highly resistant. 

The findings of this study showed that management of Ascochyta blight is essential to provide increased and stable yields where conditions are suitable for the disease. According to the results, the studied chickpea germplasm, are valuable resources, in addition to possess new traits provide high diversity for breeders to improve the new varieties and can be employed as resistant sources in chickpea breeding programs to develop resistant cultivars to Ascochyta blight.