Disease Note.

Occurrence of leptosphaeria maculans on Mustards in Brittany, France. I. Somda, INRA, Station de Pathologie Vegetale, Domaine de la Motte, B.P. 29, F 35650, Le Rheu, France. H. Brun, INRA, Station de Pathologie Vegetale, Domaine de la Motte, B.P. 29, F 35650, Le Rheu, France. Plant Dis. 79:754. Accepted for publication 18 May 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0754C.

Mustards, such as Brassica juncea (L.) Czernj. & Coss. and B. nigra (L.) W. Koch, usually develop a hypersensitive reaction at the cotyledon stage to infection by Leptosphaeria maculans (Desmaz.) Ces. & De Not. (anamorph Phoma lingam (Tode: Fr.) Desmaz.), the cause of blackleg of crucifers. Brassica juncea cv. Picra and B. nigra cv. Junius, sown with other crucifers in experimental fields in Brittany, were surveyed for blackleg canker occurrence from October 1992 to June 1993. Rare, tiny leaf lesions were observed on Picra in March 1993, while Junius remained symptomless. Although no external, typical stem or canker symptoms were found, blackening of stem tissues and fungal pseudolhe-cia were observed on both mustard species. Isolations from blackened stems and pseudothecia yielded ca. 200 isolates, which sporulated on V8-juice agar and were identified as P. lingam based on conidium morphology and size. In (he autumn of 1993, a few pseudothecia, identical to those developed on susceptible oilseed rape (B. napus L. var. oleifera (Metzger) Sink.) were observed on both mustard species, and produced asci and ascospores morphologically identical to typical L maculans. Single ascospore lines and pyenidiospore mass isolates established from Picra produced a yellow to brown-red pigment on malt agar, whereas ascospore isolates recovered on Junius failed to produce such a pigment. The pathogenicity of isolates obtained from Picra was evaluated with a cotyledon test on sets of B. juncea and B. napus cultivars. The majority of isolates were highly virulent on both species. Analysis of variability for glucose phosphate isomerase activity yielded two different, one-banded patterns, one corresponding to each of the two groups of isolates, obtained from Picra and Junius, respectively. To our knowledge, this is the first report of L. maculans occurrence on mustards.