Evaluation of Wheat Root Colonization Pattern to Be Employed in Biocontrol of Take-all Disease Caused by Fluorescent Pseudomonads

Fluorescent pseudomonads are known as some most beneficial biocontrol agents for controlling root disease because of producing a broad spectrum of antibiotics and their effective root colonization at the right time and at the right place. In this regard، the colonization patterns of four Pseudomonas fluorescence strains were investigated in 5، 12، and 21 days following sowing bacterial coated seeds in 800 gr pots، containing garden soil mixed with 8% inoculum of Gaeumannomyces graminis var. tritici (Ggt) the agent of take-all disease. Bacterial population was determined through a counting of colony forming units (cfu) at upper، middle، as well as lower parts of wheat root. The statistical relation between colonization pattern of root and the index of take-all disease was found out، studied and analyzed. The results indicated that bacterial populations are varied within different times and at different zones of the root. During the first stage of sampling the bacterial population was higher in the upper and middle parts، whereas within third time the bacterial population decreased in upper and middle parts while being increased at the lower parts of the root. The relationship between colonization pattern and disease index revealed that bacterial population significantly affect the reducing of disease intensity. The most effective bacterial population، in reducing disease intensity، was observed for mass colonization at the root apex (r2 = 0. 99. 6). It can be concluded that better and greater potential for colonization of root apex by the four tested strains is in close relationship with their ability to control take-all disease، this playing a key role in successful control of the disease by these strains.