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Lectin genes in canola (Brassica napus) confer resistance to Sclerotinia sclerotiorum

Lone Buchwaldt: Agriculture and Agri-Food Canada

<div><em>Sclerotinia sclerotiorum</em> is an unspecialized fungal pathogen of many broad leaved crops. It causes yield loss in canola worldwide by attacking the stems leading to plant wilt. A gene expression study showed differential upregulation of two lectin genes, concanavalin and curculin, 48 hr after stem inoculation of disease tolerant cultivar Zhongyou (ZY) 821 (China) compared to a susceptible line. Both genes were cloned from ZY821 and DNA sequences were aligned with the reference genomes <em>B. napus</em> (AACC), <em>B. rapa</em> (AA) and <em>B. oleracea</em> (CC) to select gene copies with amino acid variation unique to ZY821. Genes coding curculin on chromosome C6 and concanavalin on C1 were selected for separate transformation into susceptible <em>B. napus</em> DH12075 under control of the constitutive CaMV35S gene promoter. Lines with single gene inserts in a homozygous state were identified in T<sub>1</sub>-T<sub>3</sub> generations. These lines were screened for resistance by inoculating the main stem with a mycelium plug of <em>S. sclerotiorum</em> followed by measurement of lesions length 7, 14 and 21 days later. Resistant lines showed 80% and 50% reduction of lesions and no plant wilt. Mapping of sclerotinia QTL in a bi-parental DH population derived from ZY821 confirmed QTLs associated with the same lectin alleles on C1 and C6. Both lectin proteins have transmembrane domains. Other domains likely recognize and bind to fungal hyphae and may therefore trigger cell defence. Lectins are known to be abundant in <em>B. napus</em> xylem tissue, and may explain why sclerotinia was unable to cause wilt in the transformed plants.</div>