Biological control of mustard blight caused by Alternaria brassicae using plant growth promoting bacteria

Indian mustard (Brassica juncea) is an important oilseed crop in India. Among various diseases infecting mustard crop, Alternaria leaf spot also known as Alternaria blight is incited by fungus Alternaria brassicae, which majorly affects the crop production leading to a yield loss of up to 70 %. The disease is controlled by application of different fungicides prior to winter rains but it is costly and also cause pollution in the environment. This investigation was designed to explore the potential of rhizosphere bacteria to use as bio control agents for suppression of the disease. Total of sixteen bacterial isolates were isolated from the rhizosphere of mustard, tomato and brinjal and they were screened for their antagonistic activity against A. brassicae in vitro and in vivo conditions. Out of sixteen isolates, two bacterial isolates (B3 and B12) showed maximum inhibition (35 % and 38.6 % respectively) against the pathogen and also displayed high degree of secondary metabolite formation. These two bacterial isolates molecularly characterized as Pseudomonas fluorescens were further tested in green house and field conditions through seed bacterization treatment for disease suppression. Mustard seeds were treated with the bacterial solution overnight and were sown in pots and fields the next day. It was found that the disease incidence percentage of B3 and B12 was 32 % and 35 % respectively compared to control with 62.8 %. The results of the above study were highly significant in evaluation of PGPR against A. brassicae.