EFFECT OF NUTRIENT AMENDMENTS ON SUPPRESSIVENESS OF ANTAGONISTIC MICROORGANISMS TO PLANT PATHOGENS
SD SHIH and JW HUANG
Department of Plant Pathology, National Chung Hsing University, Taichung, Taiwan
Background and objectives
Each species of microorganism may respond differently to a specific nutrient amendment. Thus nutrient amendment may affect growth and survival of some plant pathogens, yet stimulate the growth and survival of other microbial populations, including antibiotic-producing bacteria, actinomycetes, and fungi . The success of biocontrol may be greatly affected by formulation of the antagonists. Formulation can also influence shelf life, and survival of the biocontrol agents. One way to enhance performance of the antagonists may be through manipulation of nutrients present in production of microbial formulations . The objectives of this study are to promote selectively antagonistic microbial populations from agricultural wastes by use of specific nutrient additives and to explore the eitect of nutrient sources on those antagonistic microbes.
Results and conclusions
A formulated medium (SSC-05 medium) consisting of spent forest mushroom compost and carbonized rice hull was amended with 0 to 500 p.p.m. of allyl alcohol, glycerol, methanol and propionaldehyde or with 0-2% (w/w) of lettuce, soybean, radish and alfalfa seed meals, respectively. In the SSC-05 medium, proliferation of bacterial populations, especially Bacillus spp., was significantly stimulated by allyl alcohol, methanol, lettuce seed meal or alfalfa seed meal 2 weeks after treatment at 24-28°C. However, population density of actinomycetes, especially Streptomyces spp., was only enhanced by amendment with alfalfa seed meal. Among the microorganisms isolated from amended SSC-05 medium, Bacillus pumilus (strain PMB-102), B. thermoglucosidasius (strain PMB-207), S. misiononsis (strain PMS- 101) and Streptomyces padanus (strain PMS-702) were most effective to inhibit growth of Botrytis elliptica, Fusarium proliferatum, F. oxysporum f.sp. cubense race 4, F. oxysporum f.sp. lactucum, F. oxysporum f.sp. niveum, F. oxysporum f.sp. raphani, Microdochium panattonianum, Colletotrichum gloeosporioidcs, Pestalotiopsis eriobotryfolia and Acremonium diospyri in potato dextrose agar plates. Twenty-nine nutrient sources and six media were used to determine the relationship of the nutritional status of the antagonists and biocontrol efficacy. Monosodium glutamate and cassava meal were more effective to enhance antagonistic ability of B. pumilus (strain PMB-102) and B. thermoglucosidasius (strain PMB-207) to B. elliptica and M. panattonianum. The soybean meal-glucose broth (SMG broth) consisting of 5.0 g soybean meal, 5.0 g glucose, 0.4g CaCO3 and 1 litre distilled water at pH 7.9-8.1 greatly stimulated the effect of S. padanus (strain PMS-702) on suppressing spore germination and mycelial growth of F. o.xysporum f.sp. cubense race 4. Our data suggest that it may be possible to enhance the level of biocontrol through manipulation of nutrient sources used for production of the antagonists.
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