Reaction of wild crucifers to Leptosphaeria maculans, the causal agent of blackleg of crucifers

Cotyledons, leaves, and stems of the wild crucifers Arabidopsis thaliana, D iplotaxis muralis, Diplotaxis tenuifolia, and Raphanus raphanistrum and cot yledons and leaves of Sisymbrium loeselii were inoculated with pycnidiospor es of an aggressive isolate of Leptosphaeria maculans, the cause of blackle g of crucifers. All species except R. raphanistrum expressed a high level o f resistance to L. maculans; the resistance was characterized by rapid cell death, tissue browning, and lignin deposition. In R. raphanistrum, the rea ction of cotyledons and leaves ranged from a hypersensitive-like response t o extensive tissue collapse and necrosis comparable to that observed in sus ceptible Brassica napus cv. Westar; stem tissue of R. raphanistrum, however , was highly resistant to L. maculans. The fungus was recovered from necrot ic cotyledon and leaf tissue of all the wild crucifers 10 and 20 days posti noculation, respectively, and from stem tissue of D. muralis around the poi nt of inoculation 40 days postinoculation.