Survey of some of ascospore characteristics of rapeseed blackleg disease for differentiating Leptosphaeria maculans and L. biglobosa in some areas of Mazandaran and Golestan provinces

Ascospore dimensions of eight populations of Leptosphaeria maculans and L. biglobosa, causal agents of rapeseed blackleg disease, isolated from debris of rapeseed (Brassica napus) and wild mustard (Sinapis arvensis) were evaluated in Mazandaran and Golestan provinces. Results of ANOVA indicated significant differences in the dimensions of ascospores of the different populations. The greatest length and width of sexual spores were 87.5 and 12.5 micrometer, respectively. Variations in the range of Length and width of ascospores in the studied populations was measured, 46.25 and 7.5 micrometer, respectively also these variations were 6.25 and 2.5 micrometers greater than the dimensions of ascospores reported by other studies in the world. The length of sexual spores isolated from stem debris of mustard was much bigger than those of canola. Germination percentage of most studied populations was more than reported in other studies, so likely the most of studied populations of different regions belong to non aggressive group. Sexual spores of aggressive types have greater number of germ tubes, shorter in length, twisted and originate from the middle cells. While in the nonaggressive type the germ tubes grow out of end cells and are not twisted. With regard to morphological characteristics of sexual spore germ tube and also cotyledon test characteristics, field symptoms, pigment production and colony growth rate it was determined that ascospores of the studied populations from Dasht-e-Naz of Sari, Kohikheil and Fazel Abad were of the aggressive type (L. maculans) and most of population in Lala, Mazarustaq and Talookola areas belonged to nonaggressive type (L. biglobosa). There was no correlation between germ tube characteristics of fungus populations on mustard and their pathogenicity.