COMPARISON OF INOCULATION METHODS FOR SELECTION OF PLANTS RESISTANT TO LEPTOSPHAERIA-MACULANS IN BRASSICA-NAPUS

The relationship between ratings following four inoculation techniques and field ratings and the usefulness of these techniques for screenin g large populations was determined. Plants of Brassica napus 'Westar,' 'Wesroona', 'Topas', 'Hanna' and 'R8314' were inoculated with L. macu lans using four techniques: cotyledon inoculation with cotyledon ratin g, leaf inoculation with leaf and stem rating, stem inoculation with s tem rating and inoculation using infested oat kernels with stem rating . Plants from each combination of cultivar and technique were self-pol linated for evaluation of disease rating in the field. The highest pre cision was obtained with cotyledon rating following cotyledon inoculat ion. The correlation coefficient between the rating of inoculated plan ts and the field rating of their progeny ranged from 0.50* for oat ke rnel inoculation to 0.72* for cotyledon inoculation. Considerable var iation for field rating was associated with each rating following arti ficial 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.