Effect of Temperatures on Inhibitory Effect of Lesion Development in the Branch Blight (Stigmina mori (Nomura) Shirata et Takahashi) by Bark-wounding of Mulberry Shoots

Abstract

The basal parts 20cm long taken from 1-year-old shoots of cv Ichinose were inoculated with Stigmina mori mycelia after making a wound (1.5×1.5mm) on the bark, then incubated at 2.5 to 30C for various durations. Size of lesions on the inner surface of bark was measured, using the equation; lesion size=√length(mm)×width(mm). The lesion could develop at 2.5 to 15C, with the optimum temperature of 10C. No development of lesion occurred at 20C where fungal growth was the highest on PDA medium. At 10C, lesion size (Y) increased with days after inoculation (X); Y=2.7X-4.3. No further development of lesion was observed even if shoots, which had been kept at 25C for 1 day after inoculation, were transfered to 10C. When shoots were wounded, kept at 5C for 2 days or at 20C for 1 day, then inoculated, majority of shoots failed to develop the lesion. This inhibitory effect was limited to 2-5mm from the wound. Whereas, inhibitory effect on fungal growth in shoots disappeared completely when shoots were stored at -60C for 60min or at 60C for 10min in water bath before inoculation. Shoots having wounds and treated with 2 or 10ppm blasticidin S (BcS) were kept at 20C and, after various intervals, inoculated with mycelia on wounds, then incubated at 10-15C. Lesion developed in BcS-treated shoots, but failed to develop in non-treated ones. When shoots were wounded, incubated at 5 or 20C for 0 to 24hr, treated with 10ppm BcS for 30min, then incubated at 10-15C for 4 days. Effect of BcS on lesion development was observed 12 and 4hr after wounding at 5 and 20C, respectively, indicating that a defence activity of wounded tissues began to appear under these conditions. The defense activity reached maximum about 24 and 8-12hr after wounding at 5 and 20C, respectively.