Expression and relationships of resistance to white rust (Albugo candida) at cotyledonary, seedling, and flowering stages in Brassica juncea germplasm from Australia, China, and India

Abstract

White rust (Albugo candida) is a highly destructive disease of oilseed Brassicas such as Brassica juncea and B. rapa. Most commercial B. juncea or B. rapa varieties are highly susceptible and yield losses from combined infection of leaves and inflorescences can be up to 20% or 60% in Australia and India, respectively. In Australia, canola-quality B. juncea has been developed to extend oilseed Brassica production into lower rainfall areas, with the first commercial B. juncea canola-quality variety planned for release in 2006. It is essential to identify useful sources of host resistance in B. juncea as breeding and/or selection of material for resistance is the most cost-effective method of delivering control for farmers. Three experiments were undertaken under controlled-environmental conditions to identify the best methods of characterising host resistance and to identify sources of resistance in B. juncea germplasm from Australia, China, and India. Forty-four B. juncea genotypes, viz. 22 from India, 12 from Australia, and 10 from China, were tested. Four Chinese genotypes (CBJ-001, CBJ-002, CBJ-003, CBJ-004) and one Australian genotype (JR049) consistently showed high resistance to A. candida across the different plant growth stages against a pathotype prevailing in Australia. Similarly, the most susceptible genotypes (viz. Indian genotypes RH781, RL1359, RH819) were extremely susceptible irrespective of the plant growth stage. Overall, although disease severity on cotyledons and leaves at the different growth stages was significantly and positively correlated, there was, however, no significant correlation between the number of stagheads and any of the other disease parameters measured. Our study demonstrates that controlled-environmental conditions are suitable for rapid identification of resistant genotypes and that genotypes with high levels of resistance can be reliably identified at the cotyledonary, seedling, or flowering stages.

Pre-inoculation with Hyaloperonospora parasitica reduces incubation period and increases severity of disease caused by Albugo candida in a Brassica juncea variety resistant to downy mildew

“…Brassica juncea variety RH 819, known to be highly susceptible to race 2 V of A. candida (Kaur et al 2008;Li et al 2007) but resistant to isolate UWA DM-53 of H. parasitica (based on previous preliminary trials; data not presented), was selected for this study. Two experiments were undertaken, and for both, seeds of variety RH 819 were sown 1 cm deep into steam-treated potting mix (composted pine bark:cocoa peat:river sand, 2:1:1) in 8-cm-diameter plastic pots in a controlled-environment room maintaining 13°C/18°C night/day temperatures, with a 16-h photoperiod at a light intensity of 520 E/m 2 /s, at the University of Western Australia, Perth, Western Australia.…”

Host Range and Phylogenetic Relationships ofAlbugo candidafrom Cruciferous Hosts in Western Australia, with Special Reference toBrassica juncea

“…The concentration of the zoosporangial suspension was adjusted using a hemaeytometer to 10' zoosporangia ml"' before application to cotyledons (33). Ten days after sowing, fully expanded cotyledons were inoculated by a drop-inoculation technique where a single lO-pl drop of the zoosporangial suspension was spotted onto the adaxial surface of each of the two lobes of eaeh cotyledon (33).…”

“…The concentration of the zoosporangial suspension was adjusted using a hemaeytometer to 10' zoosporangia ml"' before application to cotyledons (33). Ten days after sowing, fully expanded cotyledons were inoculated by a drop-inoculation technique where a single lO-pl drop of the zoosporangial suspension was spotted onto the adaxial surface of each of the two lobes of eaeh cotyledon (33). Plants were then subjected to 4 days of enhanced humidity (>98% relative humidity) in a high-humidity chamber consisting of a sealed clear plastic container, where the inside of the lid was sprayed with DI water and 1 cm of free water maintained in the bottom of the container.…”

“…White rust is an important disease of cruciferous crops in Australia, including Western Australia (W.A. ; [4][5][6][7][8][32][33][34]36). It is of particular significance to Brassica júncea, because canola-quality B. júncea is being developed in Australia to extend oilseed Brassica spp.…”

Proteome analysis of the Albugo candida–Brassica juncea pathosystem reveals that the timing of the expression of defence-related genes is a crucial determinant of pathogenesis

“…The combined infection of leaves and inflorescences causes yield losses of 20–60% (Barbetti, 1981; Bernier, 1972; Lakra and Saharan, 1989). As deployment of host resistance offers the most cost-effective and reliable means of managing this disease, studies have been undertaken to identify sources of resistance (Li et al , 2007 a , b , 2008). In particular, the recent identification of race 2V of A. candida in Australia (Kaur et al , 2008), has opened the way for investigation into the mechanism(s) associated with host resistance against this highly virulent pathogen race.…”