Author(s):

A Muthukumar and T Suthinraj

Abstract: Eight native <em>Pseudomonas</em> species (I₁ to I₈) and one introduced <em>P. fluorescens</em> (I₉)were evaluated to test the antagonism against <em>Sclerotium rolfsii </em>unde<em>r in vitro </em>conditions. Of the eight antagonists tested, isolate-I₇ (PFP) recorded the maximum inhibition zone of 13.33 mm and a minimum of 23.00 mm mycelial growth of <em>S. rolfsii </em>accounting for 74.25 per cent reduction in the mycelial growth over control (89.33 mm) and it was on par with I₉ (PFC). This was followed by isolate-I₄(PFK). The least mycelial growth inhibition was observed with the isolate-I₃(BSE). Biochemical tests were conducted for all the isolates. All the isolates produced similar result with regard to gram staining and KOH test (I₁, I_4, I_6,­ I₇, and I₈) showed negative, whereas fluorescent pigment test showed positive results. The<em> </em>isolates-I₂, I₃, I₅, showed positive in gram staining and KOH test, whereas fluorescent pigment showed negative results. Generally all the isolates showed positive results in motility test. The eight bacterial isolates tested in this experiment showed variation with colony type, colour, growth type and reaction to UV light. The effect of different concentration of culture filtrate of bacterial isolates on the mycelial growth of <em>S. rolfsii</em> under <em>in vitro</em> conditions revealed that the culture filtrate of the isolate-I₇ totally inhibited the mycelial growth of <em>S. rolfsii</em> at 15% concentration under <em>in vitro</em> conditions followed by the isolate-I_4.. Studies on the effect of antagonist under pot culture condition revealed that the combined application of <em>P. fluorescens </em>(PFP) through seedling dip (SD) and soil application (SA)<em> </em>recorded the minimum incidence of collar rot (13.66 per cent). The maximum disease incidence was recorded in inoculated control treatment (93.33 per cent).

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