Incidence of root and hypocotyl diseases in lupin crops in Western Australia between 1986 and 2005

Abstract

Three separate surveys were carried out in commercial lupin crops in the major lupin growing region of Western Australia in 1986, 1990, and 2004–05. In total, 333 sites were sampled and plants assessed for the incidence and cause of root and hypocotyl rots. Measurements were made of plant density and sowing depth at all sites. In all surveys, root rot was more common than hypocotyl rot. Root rot occurred in more than 95% of sites in each survey; however, a greater proportion of sites had high levels of root rot in early surveys. The incidence of root rot within sites decreased from an average of 34.9% in 1986 to 10.2% in 2004–05. Hypocotyl rot incidence varied among surveys, incidence of infected paddocks, and within-paddock incidence was greatest in the 1990 survey. Hypocotyl rot incidence was lowest in the 2004–05 survey. Rhizoctonia solani and Pleiochaeta setosa were commonly isolated from root lesions and R. solani was the predominant pathogen isolated from hypocotyl lesions. Analysis of the R. solani isolates by pectic zymogram showed that the ZG3 strain was most regularly isolated from roots and hypocotyls. This series of surveys indicates that the incidence of root rots in commercial lupin paddocks in Western Australia has decreased dramatically over the past 20 years; however, root rot still occurs in most paddocks regardless of soil type, location, crop rotation, and management systems.