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

Abstract

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 pyenidia 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 thai 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.