Incidence of Phomopsis phaseoli (Desm.) Sacc. in crops and seed of soybean in New South Wales

Abstract

The pod and stem blight and seed decay fungus Phomopsis phaseoli was detected in soybean crops in coastal districts of New South Wales as a symptomless infection in the lowest petioles at flowering. Up to 90% of petioles from a second year crop yielded the fungus compared with 17% from a first year crop. Similar effects of paddock history were evident during pod fill when 43% of pods from a first year crop were infected compared with 76% in a second year crop. Visible symptoms of infection only appeared after crops reached harvest maturity. Crops in the North West of the state were infected at a much lower level. As in coastal districts the highest levels of infection occurred in fields which had been sown previously to soybeans. Only negligible levels of infection were detected in crops grown in the Riverina district. Only seed from coastal crops carried significant infection with P. phaseoli. The level of infection varied within and between seasons and was determined by prevailing climatic factors, especially atmospheric humidity and rainfall during pod fill and after maturity. Humidity and rainfall are greater for coastal than for inland districts, but prevailing temperatures in coastal and inland districts are only slightly different.