Screening and Test of Biocontrol Agents Against Vanilla Root Rot
Root rot of vanilla caused by Fusarium oxysporum f. sp. vanillae and F. Solani is the most serious disease of vanilla widely distributed in vanilla plantations in China.Three strains of Trichoderma spp. and two strains of Bacillus subtilis and one strain of Pseudomonas fluorescens were assayed to test their biocontrol potentiality against the pathogens in vitro. Of all the strains,only strains OBS-2 and 1. 936 of Bacillus subtil is showed significantly inhibiting activity on the above pathogens in dual culture. In greenhouse pot trials,dipping of vanilla cuttings roots with the OBS-2 solution +application of OBS-2 bagasse preparations or OBS-2 rice stem preparations gave a 82.1% or 93.7% biocontrol effect at 30 days after treatment. Similar treatment with strain 1.936 produced a 54.1% or 45.1% biocontrol effect. Presoaking of roots of vanilla cuttings with the solution of Fusarium oxysporum f. sp. niveum 940304 yieded a 41.3% biocontrol effect at 30 days after treatment. In the field trials,soaking of vanilla cuttings roots with solution of OBS-2 and applying with OBS-2 baggasse preparations resulted in a 59.7% biocontrol effect while similar treatment with strain 1.936 only gave a 38.8% biocontrol effect,and presoaking of roots of vanilla cuttings with strain 940304 showed a 41.7%biocontrol effect at 38 days after treatment. Results showed that the native isolated strain OBS-2 of Bacillus subtilis is superior to the strain 1.936 provided from Beijing in the biocontrol potentiality.