Efficiency of Bioproduct from Bacillus subtilis Isolate 20W1 to Control Alternaria brassicicola a Causal Agent of Chinese Kale Leaf Spot

Abstract

Alternaria brassicicola can cause leaf spot symptoms at every growth stages of Chinese kale. Biological control is an alternative technique to reduce chemical usage. However, a limiting factor for biological control is the un-survival of antagonists on plant leaf surface. Bacillus bacteria can be a promising antagonist to A. brassicicola, which has a special ability in producing endospores that could tolerance and grew well in field condition. During October 2011 – September 2013, 135 isolates of Bacillus spp. isolated from soil, manure, and planting materials, were evaluated for the ability to inhibit growth of A. brassicicola using dual culture technique. Five isolates effectively inhibited mycelia growth of A. brassicicola, namely 20W1 20W5 20W4 20W12 and 17G18. These isolates were then tested for the disease control in the screen house by spraying of its cell suspension prior to the inoculation of the pathogen. We found that all isolates could effectively reduce Chinese kale leaf spot disease to 46.77%, 52.81%, 59.99%, 60.45% and 71.31% respectively compared to 73.79% of the disease in onantagonist spraying treatment. Field trial at Ta Maka District, Kanchanaburi province also showed results as similar as in screening house experiment. Those 5 isolates of Bacillus spp. were formulated into powder formulation and tested again at the same field. The results showed that all isolates could significantly control the disease better than a non-antagonist spraying
treatment. Isolate of B. subtilis 20W1 was the most effective antagonist which reduced the disease to 32.88%. Efficacy trial of the 20W1 isolate at 20-30 g/20 L of water showed the disease control at the same level as using mancozeb 80% WP at 40 g/20 L of water and significantly controlled the disease when applied at 40-50 g/20 L of water. In conclusion, B. subtilis 20W1 is a new potential isolate which can be developed to the bio-fungicide for a commercial scale.