Investigating quantitative resistance to Leptosphaeria maculans (Phoma stem canker) in Brassica napus (oilseed rape) in controlled conditions

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Abstract: Operation of quantitative resistance to Leptosphaeria maculans in Brassica napus at the seedling stage was investigated in controlled environments using doubled haploid (DH) lines A30 (very susceptible, without quantitative resistance) and C119 (with good level of quantitative resistance). These two DH lines were derived from the cross Darmour-bzh Ă—Yudal. Quantitative resistance to L. maculans at the seedling stage was investigated at two stages; growth of pathogen in leaf petioles before it reaches the stem and growth in stem tissues to form stem canker symptoms. Two types of inoculum (ascospores and conidia), two inoculation methods (leaf lamina inoculation and petiole inoculation) and different assessment methods (assess visible disease symptoms; trace symptomless pathogen growth using reporter gene GFP; quantify pathogen DNA) were used to study the quantitative resistance to L. maculans in controlled conditions. For leaf lamina inoculation, significant differences were observed between DH lines A30 and C119 in the rate of growth of GFP-expressing L. maculans and the amount of L. maculans DNA in leaf petioles. For leaf petiole inoculation, significant differences were observed between A30 and C119 in severity of stem canker and the amount of L. maculans DNA in stem tissues. These results indicate that it is possible to investigate quantitative resistance to L. maculans at the seedling stage.

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