Genetic Study and Temporal Dynamics of the Reaction to Ascochyta rabiei Epidemic in Improved Lines and Cultivars of Chickpea (Cicer arietinum L.)

Abstract

Ascochyta blight is the most devastating worldwide disease of chickpea (Cicer arietinum L.). It is caused by Ascochyta rabiei (teleomorph: Didymella rabiei) an airborne pathogenic fungus which is common in rainy climates and warm temperatures. Despite the efforts deployed by genetic improvement to develop highly resistant varieties, a total resistance to Ascochyta blight is lacking in chickpea. From 2015 to 2019 season, a study was carried out to develop highly resistant lines at the experimental station of the National Agronomical Institute of Tunis (INAT).

In this genetic program, four crosses were realized: Nour x ILC154986, Nour x ILC154445, Béja1x ILC155064, and Béja1x ILC154449. Nour and Béja1 varieties were respectively tolerant and susceptible to Ascochyta blight and were used as female parents. The genetic study showed a total of six genes controlling the resistance to Ascochyta blight. The disease progress was analyzed under inoculation in the field on seven dates, and the plant infection rate r was recorded on the parental cultivars and the lines developed from crosses. The temporal progress of the disease was studied by using statistical and mathematical tools. A logistic model was tested and then applied to describe the Ascochyta rabiei progress over time in the field. The fitting adequacy of the logistic model was estimated by the determination coefficient R² which value exceeded 0.98 and justified this selection. The logistic curves analysis showed a slow blighting and an infection progress decrease of lines issued from Béja1 x desi1 and Nour x Kabuli1 crosses. These lines obtained by transgressive segregation in the Nour x Kabuli1 and Beja1 x Desi2 populations can develop a stable resistance and prevent its overcoming.