Abstract
A Systematic survey was conducted in alfalfa fields in the middle zones of Iraq during June to November, 2001 and 2002, to detect the occurrence and distribution of alfalfa wilt disease and identification the causal agents in each field. Results revealed that the disease symptoms were very clear in most of alfalfa fields in the area. High disease incidence 37.5 and 23.3% were detected in Baghdad and Wasit respectively. Some soil borne pathogens were isolated and purified from alfalfa root samples. Fusarium solani , Fusarium oxysporum and Verticillium alboatrum were the most frequent among the isolated fungi,Mean while Pythium sp and Pencillium sp . were with low frequency. Furthermore, three Corynebacterium isolates were isolated from the infected alfalfa plants with high frequency and purified. Results revealed that Verticilium alboatrum and Corynebacterium 1 caused 49% and 45% pre-emergency damping off alfalfa seedlings respectively and also killed 100% and 95% of alfalfa plants after one month respectively when compared with the control, followed by isolate 3 of Corynebacterium and F. oxysporum 1 which killed 44 and 34% of the seedlings pre –emergency and 30 , 45% post-emergency respectively. According to these results we can consider that Verticillium alboatrum, F. oxysporum and Corynebacterium isolates are the principle causes of alfalfa wilt disease separately or in combination in alfalfa fields in the middle zone of Iraq.
