Biological control of Ascochyta blight and improvement of chickpea growth parameters by the application of arbuscular mycorrhiza and plant growth promoting rhizobacteria

Ascochyta blight disease of chickpea plants caused by Ascochyta rabiei is one of the important agents that reduce the yield of this crop around the world. In this study, the effect of separate and combined application of two arbuscular mycorrhizal fungi (AMF) including Glomus versiform and Glomus fasciculatum, and four plant growth promoting rhizobacteria (PGPR) including Bacillus subtilis BS, Bacillus velezensis JPS19, Bacillus pumilus INR7 and Alcaligenes faecalis 1624 for controlling the Ascochyta blight of chickpeas was investigated under greenhouse conditions. The fungicide chlorothalonil, which was used for comparison, was the most effective in reducing the disease. All biological treatments reduced the severity of the disease compared to the diseased control, and most of them enhanced the growth parameters (wet and dry weight of roots, wet and dry weight, and the length of foliage) in the presence of the pathogen, except for root length. Compared to the separate application of AMF, some PGPR+AMF combined treatments had a synergistic effect on disease inhibition, enhanced growth, or root mycorrhizal colonization rate, but this effect was not present in all combinations. There was no direct relationship between the amount of mycorrhizal colonization and the reduction of Ascochyta blight; In general, the use of AMF and PGPR, separately and in combination, was effective in reducing the Ascochyta blight disease and enhancing the growth of chickpeas, but the efficiency of the combined inoculation was not always synergistic and depended on the bacterial and mycorrhizal strains used.