Development of high-throughput methods to screen disease caused by Rhizoctonia solani AG 2-1 in oilseed rape

Background: Rhizoctonia solani (Kühn) is a soil-borne, necrotrophic fungus causing damping off, root rot and stem canker in many cultivated plants worldwide. Oilseed rape (OSR, Brassica napus) is the primary host for anastomosis group (AG) 2-1 of R. solani causing pre- and post-emergence damping-off resulting in death of seedlings and impaired crop establishment. Presently, there are no known resistant OSR genotypes and the main methods for disease control are fungicide seed treatments and cultural practices. The identification of sources of resistance for crop breeding is essential for sustainable management of the disease. However, a high-throughput, reliable screening method for resistance traits is required. The aim of this work was to develop a low cost, rapid screening method for disease phenotyping and identification of resistance traits. Results: Four growth systems were developed and tested: (1) nutrient media plates, (2) compost trays, (3) light expanded clay aggregate (LECA) trays, and (4) a hydroponic pouch and wick system. Seedlings were inoculated with virulent AG 2-1 to cause damping-off disease and grown for a period of 4–10 days. Visual disease assessments were carried out or disease was estimated through image analysis using ImageJ. Conclusion: Inoculation of LECA was the most suitable method for phenotyping disease caused by R. solani AG 2-1 as it enabled the detection of differences in disease severity among OSR genotypes within a short time period whilst allowing measurements to be conducted on whole plants. This system is expected to facilitate identification of resistant germplasm

Brassica napus plants infected by Leptosphaeria maculans after the third to fifth leaf growth stage in south-eastern Australia do not develop blackleg stem canker

The original publication can be found at www.springerlink.comBlackleg (Phoma stem canker) caused by Leptosphaeria maculans is the most damaging disease of Brassica napus (canola, rapeseed, colza) worldwide and is controlled by sowing blackleg resistant cultivars and crop management strategies that reduce exposure to inoculum and fungicide application. In experiments in south-eastern Australia, canola cultivars inoculated after the three to five leaf growth stage did not develop stem canker. Although mature canola plants are known to be less susceptible to blackleg than seedlings, this highlights for the first time the specific importance of protecting seedlings up to the three to five leaf growth stage in Australia. This would typically correspond to a period of four to six weeks after emergence. Canola plants are likely to be significantly less vulnerable to infection after this growth stage. However, this timing may vary due to the influence of environmental conditions.S.J. Marcroft, M.R. Sosnowski, E.S. Scott, M.D. Ramsey, P.A. Salisbury, B.J. Howlet

World-wide importance of phoma stem canker (Leptosphaeria maculans and L-Biglobosa) on oilseed rape (Brassica napus)

Phoma stem canker is an internationally important disease of oilseed rape (Brassica napus, canola, rapeseed), causing serious losses in Europe, Australia and North America. UK losses of Euro56M per season are estimated using national disease survey data and a yield loss formula. Phoma stem canker pathogen populations comprise two main species, Leptosphaeria maculans, associated with damaging stem base cankers, and Leptosphaeria biglobosa, often associated with less damaging upper stem lesions. Both major gene and quantitative trait loci mediated resistance to L. maculans have been identified in B. napus, but little is known about resistance to L. biglobosa. Leptosphaeria maculans, which has spread into areas in North America and eastern Europe where only L. biglobosa was previously identified, now poses a threat to large areas of oilseed rape production in Asia. Epidemics are initiated by air-borne ascospores; major gene resistance to initial infection by L. maculans operates in the leaf lamina of B. napus. It is not clear whether the quantitative trait loci involved in the resistance to the pathogen that can be assessed only at the end of the season operate in the leaf petioles or stems. In countries where serious phoma stem canker epidemics occur, a minimum standard for resistance to L. maculans is included in national systems for registration of cultivars. This review provides a background to a series of papers on improving strategies for managing B. napus resistance to L. maculans, which is a model system for studying genetic interactions between hemi-biotrophic pathogens and their hostsPeer reviewe