Abstract:
As agriculture forms a major part of economy in Sri Lanka and plant diseases are
responsible for large economic losses, more attention is required on plant disease control. In this
investigation sesame {Sesamum indicum L.) has been selected because of its importance as a oil
seed crop and is vulnerable to number of diseases including more serious soil borne diseases. The
pathogen selected was Rhizoctonia so/ani which is a causative agent of seedling damping off. The
attention was focused on biological control. As soil borne pathogens have to encounter,
rhizosphere microorganisms before entering into roots, the most appropriate site for selecting
biological control agents in the rhizosphere.
Therefore rhizosphere microorganisms have been isolated using different culture media and
identified as far as possible. The common species were for the characterized by electrotyping. As
it known that different varieties of a host species can harbor different rhizosphere organisms, three
varieties of sesame were used as hosts. The evolution of rhizosphere microflora with age was also
followed.
When tested in vitro antagonism in dual culture plates, several Bacillus subtilis and
Pseudomonasfluorescens electrotypes were successful. However only P. fluorescens electrotype
s2 was effective in controlling the disease in pot experiments. The importance of electrotyping in
screening for biocontrol agents against other rhizosphere organisms and use of as many different
culture media as possible is stressed.
