Their relative abundance and interaction is poorly understood, but there is evidence that high populations of microbes such as Trichoderma spp. and Pseudomonas spp. can reduce disease risk.
In the past, it was difficult to identify and quantify "rhizosphere" microbial communities. Recently, a novel molecular method known as terminal restriction fragment length polymorphism (T-RFLP) permitted simultaneous identification and relative quantification of micro-organisms in a single test.
T-RFLP detects pathogenic and saprophytic microbes including both culturable and non-culturable organisms. It was used in HDC project PC 281 to investigate the occurrence and relative levels of major pathogenic and non-pathogenic micro-organisms associated with roots of tomato crops in different media. The data was examined to determine whether it could be used to predict the risk of root disease.
T-RFLP analysis indicated more than 100 species of fungi and bacteria associated with tomato roots. Growing media type had a large effect on fungal population diversity, being least in nutrient film and greatest in the soil. Fungal diversity increased progressively with time in rockwool, nutrient film and coir crops, but decreased in soil crops.
Plant health and root rot at the end of the season was not found to be associated with fungal or bacterial diversity indices determined in cropping. In plants with obvious root mat disease or Pythium root rot, fungal and bacterial species richness was greater, possibly a result of secondary colonisation by micro-organisms.
Horticultural Development Company
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