Distribution, Virulence and Diversity of Leptosphaeria maculans and Leptoshaeria biglobusa at Major Brassica Growing Areas of Ethiopia

A study was conducted to investigate the virulence and diversity of blackleg in major brassica growing areas of Ethiopia. The highest blackleg severity was recorded at Holeta on station canola type cultivar with severity range of 3.5% to 25.6%. The rest visited fields were free from black leg disease. Most of the fields were found covered with Brassica carinata which is under species has BB genome which confers resistance to blackleg. A total of 48 fungal isolates were recovered from leaves and steam of Brassica species. 52% of the isolate goes to L. biglobusa followed by L. maculans 31.25%. Morphological characteristics of the isolates were studied on a PDA medium at 25 ± 1°C: Colonies were found circular in shape after 5 days, and were observed in isolates: BLHH-1, BLHH-2, BLHH-3, BHLL-4, LM-1, LM-2, LB-1, and LB-2. Mycelia were loose, colored white to white smoke. Some of them form colonies with irregular round shape and lobular edges. The pycnidia of the fungus were black, globose to subglobose in shape, the single-celled conidia, hyaline and fusiform with diameters of 4–5 × 1.5–2 μm. From the result slow growth was observed on L. maculans isolate with high sporulation, whereas faster growth rate was observed on L. biglobosa with low sporulation. For the purpose of isolates separation, based on pigment formation on liquid Czapek agar, it was observed that after 30 days isolates LM-1, LM-2, LB-1 and LB-2 where produce yellow-brown pigment which indicate places isolates in a group of non-aggressive strains in conformity with the L. biglobosa. Isolate BLHH-1, BLHH-2, BLHH-3 and BLHH-4 which did not produce pigment; the situation indicates the aggressiveness of the isolate and which is under group L. maculans. Blackleg were found less distributed in major growing areas of Ethiopia, however L. maculans and L. biglobosa were confirmed their presence based on morphological and cultural characteristics. So in line with resistance variety development other management options need to be address to make rapeseed return to production.