study of antagonistic mechanisms of bacillus spp. in biocontrol of cucumber root and foot rot caused by pythium ultimum and p. aphanidermatum

abstract a total of 270 bacillus strains were isolated from bulk soil and rhizospheric of cucumber in the tonekabon fields (mazandaran province). antifungal activity of bacillus strains was evaluated against pythium aphanidermatum and p. ultimum using dual culture method. 13 strains with more than 10 mm inhibition zone were selected for further study. morphological, physiological, biochemical and protein pattern study of the strains showed that they are belong to bacillus subtilis (b2, b3, b4, b5, b6, b7), b. marinus (b1, b13) b. licheniformis (b9, b8), b. circulans (b10, b12), and bacillus sp.(b11). antifungal activity of the liquid and volatile metabolites of the strains of bacillus spp. on pythium spp. as well as, their potential to produce antibiotic surfactin and enzymes protease and cellulose were studied as antagonistic mechanisms of the bacterial strains. results indicated very different comportment of strains against two pythium species. more important variation was noted for liquid and volatile metabolites of strains on the mycelial growth of pythium strains b12, b11, b7, b3 and b9, b8, b6, b3 inhibited 100% mycellial growth of p. ultimum respectively. while b14 (liquid metabolites) and b11 (volatile metabolites). showed very weak inhibitory effect (13.7, 4.44. % ). in greenhouse experiment all strains were able to control of the diseases intensity of seedlings in different rates. strains b7, b8, b13, and b14 were more efficient, they reduced the rate of rotted roots caused by both pythium species between 75 to 100%. strains b7 and b13 demonstrated also important growth promoting effect on the cucumber seedlings. they increased the seedling wet weight of the varieties superdominos and french net- wet at the rate of 85.6 and 44.4% related to control respectively. the correlation between antagonistic mechanism index, evaluated in vitro, and biocontrol potential of strains in greenhouse indicated, that there is a good correlation between inhibitory effect of liquid metabolite on mycelia growth of pythium species and their biocontrol potential index. the correlation index were -0.67 and -0.45 for p. aphanidermatum and p. ultimum respectively. there was a high and significant correlation between the effect of strains on seedling growth and the root rot index in greenhouse. the correlation index was -0.93 and -0.79 for p. aphanidermatum and p. ultimum respectively.