Comparison of inoculation methods for selection of plants resistant to Leptosphaeria maculans in Brassica napus

Abstract

The relationship between ratings following four inoculation techniques and field ratings and the usefulness of these techniques for screening large populations was determined. Plants of Brassica napus ’Westar,’ ’Wesroona’, ’Topas’, ’Hanna’ and ’R8314’ were inoculated with L. maculans using four techniques: cotyledon inoculation with cotyledon rating, leaf inoculation with leaf and stem rating, stem inoculation with stem rating and inoculation using infested oat kernels with stem rating. Plants from each combination of cultivar and technique were self-pollinated for evaluation of disease rating in the field. The highest precision was obtained with cotyledon rating following cotyledon inoculation. The correlation coefficient between the rating of inoculated plants and the field rating of their progeny ranged from 0.50** for oat kernel inoculation to 0.72** for cotyledon inoculation. Considerable variation for field rating was associated with each rating following artificial inoculation. Selection of resistant plants using low cotyledon reaction was a more efficient technique than leaf or stem inoculation; it was rapid, required less labour and space and correlated well with the field ratings. Key words: Leptosphaeria maculans, Brassica napus, blackleg, oilseed rape, inoculation methods, canola