A study on integrated control of soilborne diseases of scarlet runner bean

Scarlet runner bean (Phaseolus coccineus L.) is a twining perennial vine that is grown worldwide as an annual for its showy flowers and edible pods. A high quality large seed cultivar "Hitachi-ohguro" of this plant was recently bred by Plant Biotechnology Institute in Ibaraki Prefecture, Japan. Since this cultivar was commercially produced in 2003, four severe soilborne diseases have been occurred. In this paper, identifications and control measures were discussed based on our previous reports. Several new findings on the control measures were also implemented. The four soilborne pathogens including Sclerotium rolfsii Saccardo, Rhizoctonia solani Kühn AG1, Pythium myriotylum Drechsler, and P. aphanidermatum Fitzpatrick were found to be associating the diseases and were described as newly recorded pathogens on this plant. P. aphanidermatum was the most devastating pathogen among of them. Field examinations were conducted during every summer from 2003 to 2010, and demonstrated that the disease control was succeeded with less cost by combinations of several control measures including 1) crop rotations with Dioscorea batatas Decaisne, 2) seedling protection by using a paper pots, 3) mulching using a sunlight reflecting plastic film, 4) piling soil up around the base of the plant as it grows, 5) seedling treatments by azoxystrobin and metalaxyl M, 6) application of a phosphorous acid-based fertilizer, and 7) a commercial biocontrol agent. Among of these control measures, the 1), 2) and 3) were necessary, less cost and environmentally friendly to prevent the diseases. These disease control effects would be due to the diverse soil microbial populations and their vitality. Because high microbial diversity was observed in the controlled soils by analysis of the soil microbial diversity vitality value (SMDVV) and a soil dilution plating technique.