Evaluation of Sclerotinia Stem Rot Resistance in Oilseed Brassica napus Using a Petiole Inoculation Technique Under Greenhouse Conditions

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Abstract
A petiole inoculation technique was adapted for evaluating resistance of oilseed Brassica napus seedlings to Sclerotinia sclerotiorum. In the first of four experiments, four isolates of S. sclerotiorum were tested, two originating from soybean and two from B. napus. In all, 10 to 47 B. napus accessions were inoculated in the seedling stage and responses to isolates were evaluated using days to wilt (DW) and a lesion phenotype index (LP). There were no significant differences in virulence among the four isolates for DW and only slight differences for LP. However, significant differences (P < 0.0001) were observed among the B. napus accessions for DW and LP in this experiment and in subsequent experiments using one isolate. The responses of accessions were consistent among experiments and among evaluation criteria. Higher levels of resistance were found among winter-type than spring-type accessions, and among rapeseed-quality compared with canola-quality accessions. The most resistant accessions id... White mold, caused by Sclerotinia sclerotiorum, is one of the most destructive diseases of Brassica spp. No completely resistant germ plasm has been identified, and no standard screening method has been reported. To establish a reliable screening method and identify resistant sources of oilseed Brassica napus (canola), we adapted a petiole inoculation technique developed for soybean to B. napus. In this study, we conducted several experiments under greenhouse conditions involving different isolates and a large number of B. napus accessions with different growth habits and seed qualities. We found that there were no significant differences among S. sclerotiorum isolates from soybean and B. napus species. We also found that the accessions exhibited a range of responses, and the responses were consistent among experiments and evaluation methods. The most resistant accessions showed consistently higher levels of resistance at both seedling and flowering stages. These results indicated that this inoculation me...
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