**1. Introduction**

Blackleg disease caused by the heterothallic ascomycete fungus *Leptosphaeria maculans*(Desm.) Ces. et de Not. (anamorph: *Phoma lingam* Tode ex Fr.), is the major disease of Brassica crops such as turnip rape *(Brassica rapa* L. syn. *B. campestris;* 2n = 2x = 20, genome AA), cabbage (*B. oleracea* L.; 2n = 2x = 18, genome CC), rapeseed (syn. canola or oilseed rape *B. napus* L.; 2n = 4x = 38, genome AACC), and *B. juncea* L. (Indian or brown mustard; 2n = 4x = 36, genome AABB) grown in temperate regions of the world. It was recorded for the first time on stems of red cabbage [1]. *B. napus* originated as a result of natural interspecific hybridization and genome doubling between the monogenomic diploid species, *B. rapa* and *B. oleracea,* in southern Europe approximately 10,000–100,000 years ago [2, 3]. However, it was selected and grown as an oilseed crop only 300-500 years ago [4, 5]. *B. napus* originally evolved as a spring or semi-winter type under the Mediterranean climates, and spread rapidly from southern to northern Europe after the development of winter *B. napus* varieties [6]. Both spring and winter types are affected by blackleg disease, particularly in Australia, Europe and North America. Currently *B. napus* is the world's third most important oilseed crop, grown on an area of over 23 million hectares and produce almost 53.3 million tonnes annually [7]. Increase in *B. napus* production has been attributed to the development and release of high yielding superior varieties including hybrids having traits such as high oil content, improved protein quality and herbicide resistance for better crop management.

Among the bacterial, fungal, viral and phytoplasmic-like diseases, blackleg is the most important global disease of *B. napus* crops and causes annual yield losses of more than \$900 million in Europe, North America and Australia [8-10]. *L. maculans* has an ability to kill plants even at the seedling stage, infecting cotyledons, leaves, stems, roots and pods. Under epiphy‐ totic conditions,thisdisease cancauseyieldlossesofupto90per cent[11 - 13].Therefore, control of blackleg disease has been one of the major objectives of many *B. napus* breeding programs.

© 2013 Raman et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Raman et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **2. Symptoms**

Blackleg disease causes two distinct symptoms; leaf lesions and stem canker. Outbreak of the fungus is characterised by dirty-whitish spots on leaves with small dark fruiting bodies (pycnidia). Black lesions are generally also seen on the leaves and deep brown lesions with a dark margin can be seen on the base of stem [11]. In severe epidemic conditions fungus girdles the stem at the crown, leading to lodging of the plant and possible severance of the stem. Typical lesions of blackleg can also occur on pods. Pod infection may leads to premature pod shatter and seed infection.
