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Agrobacterium Concentrations and Severity of Bronze Wilt Symptoms in Cotton Cultivars Treated with Fungal Biocontrol Agents at Planting

Alois A. Bell

ABSTRACT

The fungi, Trichoderma virens (Isolates GV4 and GV6), Trichoderma koningii x T. virens fusant #12, Gliocladium catenulatum, Gliocladium roseum, Fusarium oxysporum,and Fusarium solani were tested for their ability to colonize roots, to affect Agrobacterium tumefaciens colonization and bronze wilt severity and to affect yield. The fungi were tested with both ‘Paymaster 1220 BG/RR’ and ‘Stoneville 373’ cultivars grown with low and optimal phosphorus fertilization and with and without inoculation of soil with Agrobacterium tumefaciens isolate 25A. Stable concentrations of all fungi developed in roots within a few weeks after planting, indicating the potential for season-long effects on rhizoplane populations of other microorganisms. Some of the rhizoplane inhabiting fungi, especially Fusarium species, significantly increased yields suppressed establishment of Agrobacterium from infested seed and decreased bronze wilt severity when phosphorus levels were low. The treatments, however, were not effective when A. tumefaciens isolate 25A was added to soils. Under conditions of optimal phosphorus availability Gliocladium and Fusarium species often caused yield losses and increased Agrobacterium concentrations in roots. T. virens isolates GV4 and GV6 did not significantly affect yield, Agrobacterium concentrations or bronze wilt severity. The rhizoplane inhabiting fungi do not appear to be desirable for controlling Agrobacterium root rot or bronze wilt under recommended cultivar practices.





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Document last modified 04/27/04