PATHOGENICITY OF 3 ISOLATES OF LEPTOSPHAERIA-MACULANS ON BRASSICA SPECIES AND OTHER CRUCIFERS

Three isolates of Leptosphaeria maculans, LEROY, WR5, and UNITY (highly, moderately, and weakly virulent, respectively, on Brassica napus cv. Westar), were used to inoculate cotyledons of 17 crucifer cultivars/strains and seedling leaves of two cereals. B. oleracea was the most susceptible to all of the isolates, followed by cultivars of B. napus,, and B. campestris. Lesions caused by LEROY and WR5 on B. oleracea, B. napus, and B. campestris were characterized by extensive tissue collapse and the presence of pycnidia. Lesions on other combinations of host and isolate were usually limited to the blackening of tissue around the point of inoculation. None of the isolates caused lesions on Descurainia sophia, Capsella bursa-pastoris, or on the cereals. In another study, the leaves of 3-week-old crucifers were inoculated with each of the isolates. Basal stem lesions and internal blackening of stem and root tissues were observed for many combinations of crucifer and isolate. All isolates of L. maculans were recovered from the basal stems and roots of all inoculated crucifers except D. sophia, C. bursa-pastoris, and Thlaspi arvense; however, the weakly virulent isolate was also recovered from T. arvense. The isolates were sometimes recovered from symptomless basal stem and root tissue of inoculated crucifers. © 1990 Taylor & Francis Group, LLC.