Suppression of Diaporthe phaseolorum f. sp. meridionalis in soybean stems by Chaetomium globosum

The effect of two isolates of Chaetomium globosum (CgA-1, a producer and CgNA, a non-producer of antibiotic in vitro ) on the sporulation of pycnidia and survival of Diaporthe phaseolorum f. sp. meridionalis ( Dpm ) in soybean stems was determined under conditions of intermittent wetting and drying. Dpm -colonized stems placed on the surface of field soil or of quartz gravel were exposed to a 12- or 24-h wet period followed by a 48-h drying period until a cumulative wetness duration of 120, 240 or 480 h was attained. Both isolates reduced the pycnidia sporulation index to zero within 120 h of cumulative wetness duration if the wet period was 24 h. With a 12-h wet period the sporulation index decreased gradually, to between 4 and 8% after 480 h of cumulative wetness. In general, on the soil surface and with a 12-h wet period, CgA-1 reduced sporulation more efficiently than CgNA whereas with a 24-h wet period there was no difference between the isolates. Recovery of Dpm from C. globosum -treated stems decreased gradually with increase in wet period and cumulative wetness duration. The recovery rate from stems treated with isolate CgA-1 was always significantly less than that from stems treated with CgNA. In glasshouse experiments, disease incidence and the proportion of the stem length colonized by Dpm at the V₆ growth stage was reduced significantly when soybean seeds treated with ascospores of C. globosum were sown in Dpm -infested soil. Incorporation of bran inoculum of either of the isolates in the upper soil layer dramatically reduced disease incidence. Isolate CgA-1 reduced the disease more efficiently than CgNA.