Both incidence and severity of white rust disease reflect host resistance in Brassica juncea germplasm from Australia, China and India C.X. Li a , K. Sivasithamparam b , G. Walton c , P. Fels c , M.J. Barbetti a,c, * a School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia b School of Earth and Geographical Sciences, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia c Department of Agriculture and Food Western Australia, Baron-Hay Court, South Perth, WA 6151, Australia Received 7 May 2007; received in revised form 5 October 2007; accepted 6 October 2007 Abstract White rust (Albugo candida) is a highly destructive disease of oilseed Brassicas such as Brassica juncea and B. rapa, and has caused serious yield losses in Australia, China and India on both species. The first commercial B. juncea varieties are now being deployed in Australia, but their response to Australian strains of A. candida is yet to be defined under Australian field conditions. To identify useful sources of host resistance for Australia, China and India, in B. juncea, three field trials were undertaken in Western Australia. Forty-four B. juncea genotypes, viz. 22 from India, 12 from Australia and 10 from China, were tested. Varying levels of host resistance to Australian strains of A. candida (race 2) were identified among the genotypes from the three countries. Genotypes CBJ-001, CBJ-003 and CBJ-004 from China consistently showed high levels of resistance to A. candida on leaves across the three trials. Overall, the genotypes from China showed the best resistance, followed by the genotypes from Australia, with those from India being the most susceptible. The most susceptible genotypes were RL1359, RH30 and Seetha from India. It is noteworthy that both the incidence and severity of disease reflected varying levels of host resistance in the germplasm from the three countries, irrespective of whether screening was undertaken in the field using natural or artificial inoculation. Differentiation of resistance among these genotypes was similar to that we reported previously for artificially-inoculated seedlings or adult plants under glasshouse conditions, indicating that a choice of options is available to plant breeders to reliably differentiate host resistance among genotypes to white rust in B. juncea. # 2007 Elsevier B.V. All rights reserved. Keywords: Brassica juncea; Germplasm; Albugo candida; White rust; Resistance; Screening 1. Introduction White rust, caused by Albugo candida, is a common disease of many economically important cruciferous vegetables and oilseed crops. Significant yield losses from this disease have been reported on the oilseeds B. rapa and B. juncea and, to a lesser extent, on susceptible lines of B. napus (Harper and Pittman, 1974; Verma and Petrie, 1980; Barbetti, 1981; Fan et al., 1983; Mukherjee et al., 2001). It has been estimated that combined infection of leaf and inflorescence causes yield losses of up to 60% or more in India (Lakra and Saharan, 1989), and losses of up to 20% in Australia (Barbetti, 1981; Barbetti and Carter, 1986). To date, more than 10 distinct biological races of A. candida have been identified and classified based on host specificity (Pound and Williams, 1963; Petrie, 1975; Hill et al., 1988). Race 2 is known to affect B. juncea (Petrie, 1994; Verma et al., 1999; Rimmer et al., 2000) and is confirmed to be present on B. juncea in Australia (Gurung et al., 2007). This disease appears as both local and systemic infections (Walker, 1957). Localized infections are shown as scattered zoosporangial pustules on cotyledons, leaves and/or stems, while systemic infection occurs in developing stems and pods and shows as deformed inflorescences commonly referred to as ‘‘stagheads’’ (Verma and Petrie, 1980). While a number of chemicals and cultural means have been suggested for control this disease (Verma and Petrie, 1979; Barbetti, 1981, 1988a, b), the most efficient and cost effective www.elsevier.com/locate/fcr Available online at www.sciencedirect.com Field Crops Research 106 (2008) 1–8 * Corresponding author at: School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling High- way, Crawley, WA 6009, Australia. Tel.: +61 8 64883924; fax: +61 8 64887077. E-mail address: mbarbett@cyllene.uwa.edu.au (M.J. Barbetti). 0378-4290/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2007.10.003