Increase in defense response of biocontrol agents for reduction of Cercospora leaf spot of greengram (Vigna radiata L.)

Abstract

In addition to the prevalent practice of seed inoculation with nitrogen fixing bacteria, several other biological control agents are also applied to green gram in the form of seed treatment particularly for organic cultivation of green gram. To study the effect of such seed inoculation treatments with biological agents on reduction of cercospora leaf spot disease as well as its component characters, a field experiment was conducted during summer season, 2015 at the organic plot of the Instructional Cum Research (ICR) Farm of Assam Agricultural University (AAU), Jorhat. Seeds of green gram variety Pratap (SG-1) were treated with microbial formulations of Rhizobium, Bacillus megaterium, Trichoderma harzianum, Trichoderma viride and their combinations. The seven treatments consisted of-Rhizobium (T1), Trichoderma harzianum (T2), Trichoderma viride (T3), Bacillus megaterium (T4), Trichoderma harzianum + Trichoderma viride + Bacillus megaterium (T5), Rhizobium + Trichoderma harzianum + Trichoderma viride + Bacillus megaterium (T6) and Control (T7). The experiment was laid out in Randomised Block Design with four replications. The unit plot size was 1.5 m x 3 m with a row to row spacing of 30 cm and 10 cm between plants. Seeds treated with combined inoculation of Rhizobium @ 4 g + Bacillus megaterium @ 5ml/1000 ml of water + Trichoderma harzianum @ 5ml/1000 ml of water + Trichoderma viride @ 5ml/1000 ml of water (T6) recorded significantly higher response in terms of reduction of percentage of disease occurance. These results, thus, indicated that the combined inoculation treatment of Rhizobium with other biological agents improves vigour characteristics, seed yield as well as increasing the efficiency of defense response mechanism thereby reducing the occurance of cercospora leaf spot in green gram.