EFFECT OF PHYTOPHTHORA ROOT AND STEM ROT ON THE RESPONSE OF FIELD-GROWN SOYBEAN TO SATURATED SOIL CULTURE

Phytophthora root and stem rot, caused by Phytophthora megasperma Drechs. f. sp. glycinea Kuan & Erwin, is an important disease of soybean in several major growing areas across the world. Susceptible genotypes can be completely devastated, but cultivars with a high level of field resistance are available. Although high soil moisture is known to predispose to infection by Phytophthora, in the absence of this disease soybean is relatively tolerant to soil waterlogging, and has been shown to respond positively to continuous watering in the Saturated Soil Culture (SSC) system. The impact of Phytophthora on plants grown in SSC was investigated at two sites in south-east Queensland. At both sites, there were no differences between plants grown in SSC and conventional furrow-irrigated treatments in the rate or ultimate extent of disease development: susceptible cultivars succumbed to the disease, while cultivars with field resistance remained free of symptoms. A fungicidal seed dressing improved emergence and reduced initial disease infection, and improved seed yield in some cultivars. It was concluded that Phytophthora root and stem rot is not a limitation to the use of Saturated Soil Culture in soybean providing resistant cultivars are available.