The effect of fungicide selected Pseudomonas spp. on plant growth
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Studies conducted in cucumber (Cucumis sativa L.) and Leatherleaf fern (Rumohra adiantoformis [Forst.] Ching) were 1. Pseudomonas spp. modifies cucumber (Cucumis sativa L.) growth; 2. The effect of Pseudomonas spp. on cucumber (Cucumis sativa L.) at different inoculum levels; and 3. Fungicide promoted Pseudomonas spp. and their long-term effects on Leather leaf fern yield. The leatherleaf fern industry has experienced significant yield reduction and frond distortion in ferneries previously treated with the fungicide Benlate 50 DF. Previous research showed that Benlate 50 DF promoted Pseudomonas spp. which was detrimental to plant growth. Current studies found that the Pseudomonas spp. found in leatherleaf fern significantly reduced shoot and root growth of cucumber seedlings used as an indicator plant. This effect on plant growth was related to higher concentrations of the Pseudomonas spp., isolated from the rhizosphere of leatherleaf fern, being present in the root zone of the cucumber plant. The effect of deleterious bacteria at different inoculum density on cucumber growth was determined. Results showed that inoculum density determined the plant reaction to Pseudomonas spp. inoculation. Bacteria did not affect plant growth at high dilution levels whereas inoculation reduced plant growth at low dilution levels. Evaluation of two leatherleaf ferneries, one treated numerous times with Benlate 50 DF and the other untreated, determined that the Pseudomonas spp. causing growth problems in the cucumber bioassay were present at higher levels in the rhizosphere and endophytically in the leatherleaf plants previously treated with Benlate 50 DF. This elevated level of Pseudomonas spp. found in the Benlate 50 DF treated fernery was a long-term change in the microbial population as the last application of Benlate 50 DF was over 11 years ago. The Pseudomonas spp. elevated were identified as producers of the growth regulator IAA which has been reported in the literature to cause yield reduction and distortion in the leaves of plants when present at higher concentrations. Results from these studies confirmed the promotion of deleterious microbes from the use of Benlate 50 DF and this elevation in numbers present in the rhizosphere and endophytically was a long-term effect resulting from the use of this fungicide.