Efficacy of some Bacillus antagonist for controlling Alternaria brassicicola, causal agent of Chinese kale leaf spot
Abstract: Efficacy tests of Bacillus antagonists were investigated under laboratory, net houseand field trials. In the laboratory, one hundred and thirty five isolates of Bacillus sp. isolated fromsoil, manual and planting material, were tested on a A. brassicicola fungus for growth inhibitioncharacter by dual plate technique. The results revealed that 90 isolates could inhibit theA. brassicicola mycerial growth on PDA medium and 5 isolates showed high effectiveness. Inscreen house test, spraying with cell suspension of the 5 Bacillus sp. isolates showed that all ofthem could reduce leaf spot symptom on Chinese kale when compared to water sprayingtreatment. Among them, isolate 20W12 showed the highest effectiveness in controlling Chinesekale leaf spot. Under field condition, cell suspension spraying test were conducted during dryperiod (December, 2010 to February, 2011) and rainy period (June to August, 2011) atKanchanaburi province. Eight treatments with 4 replications in RCBD; spraying with each of 5cell suspension of Bacillus sp. isolates, A. brassicicola inoculation (C+), water spraying (C-) andspraying with solution of 40 grams of mancozeb 80% WP in 20 liters of water, on 35 days oldChinese kale plants, 48 hours before and 48 hours after A. brassicicola inoculation were used.During January to March, 2012, the 5 Bacillus sp. isolates in the form of wettable powdersuspension were conducted at the same field as previous trials. The results showed that in dryperiod, 5 isolates of Bacillus sp. cell suspension could reduce the disease better than waterspraying treatment, but they have no statistical difference when compared to mancozeb treatment.These 3 isolates which showed the highest efficacy in dry period were 17G18 20W5 20W1 and inrainy period were 20W4 20W1 and 20W12. The results from applying with wettable powderformulation of isolates 20W1 20W5 and 17G18 showed highly effective. Identification of those 5Bacillus isolates by API technique revealed that 20W5 20W12 20W4 and 20W1 were B. subtilisand 17G18 was B. licheniformis.