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

Cotyledons, leaves, and stems of the wild crucifers Arabidopsis thaliana, Diplotaxis muralis, Diplotaxis tenuifolia, and Raphanus raphanistrum and cotyledons and leaves of Sisymbrium loeselii were inoculated with pycnidiospores of an aggressive isolate of Leptosphaeria maculans, the cause of blackleg of crucifers. All species except R. raphanistrum expressed a high level of resistance to L. maculans; the resistance was characterized by rapid cell death, tissue browning, and lignin deposition. In R. raphanistrum, the reaction of cotyledons and leaves ranged from a hypersensitive-like response to extensive tissue collapse and necrosis comparable to that observed in susceptible Brassica napus cv. Westar; stem tissue of R. raphanistrum, however, was highly resistant to L. maculans. The fungus was recovered from necrotic cotyledon and leaf tissue of all the wild crucifers 10 and 20 days postinoculation, respectively, and from stem tissue of D. muralis around the point of inoculation 40 days postinoculation.