Vegetables and oil seeds Brassica are most important crops worldwide where the crops suffer different diseases. Alternaria spot/blight is severe seed-borne fungal disease. By the disease more than 90% of various Brassica seeds are infected by the disease where upto 30% yield loss has been reported specially in oil seed brassica in Bangladesh and 35-40% in India. Existing of various sources of inoculum and wide range in spore dispersal with uncertainty of the level of disease, the disease is very difficult to manage although several protective fungicides are effective in controlling the disease which is not environmentally friendly. For controlling the disease, host resistance is recognized as one of the most economic and effective control measure. In this book we discussed about our developed methods of different stages of plantlet for searching resistance against the disease. We tried to explain about the resistance of plant and its inheritance in molecular level through our research works. We do hope that the information given in this book will be helpful those who are working or will work in this field.