Abstract:
The present investigation was undertaken to assess the effects of plant
protection chemicals on the important fungal pathogens and phylloplane
microflora of rice. An attempt has been made to identify potential biological
control agents to combat sheath blight disease causing havoc to rice
cultivation in Kerala.
Both under pot culture conditions and during the course of field trials
at two locations viz., Adoor and Karamana, Kerala, the fungicide carboxin
was found to be the best treatment for reducing the incidence and intensity of
sheath blight and sheath rot diseases of rice. The fungicide was found to be
the least harmful to the epiphytic microflora of the rice plant. In some
instances the population of phylloplane antagonists of R. solani, including
Trichoderma harzianum, T. viride, Penicillium oxalicum and Aspergillus
aculeatus were found to be enhanced by the application of carboxin.
The total disease incidence and yield loss were significantly reduced by
the application of edifenphos. The rice variety Karthika was found to be
significantly tolerant to sheath blight and sheath rot compared with the rice
variety Jyothy.
The fungicides carboxin and mancozeb at 500ppm did not inhibit the
growth of the phylloplane antagonists of R. solani viz., Trichoderma
harzianum and T. viride under in vitro conditions.
Several micro-organisms isolated from the rice phylloplane were found
to exhibit in vitro antagonism towards R. solani. These include Aspergillus
aculeatus,
A.
niger,
Chaetomium
globosum,
Penicillium
oxalicum,
Trichodema harzianum, T. viride, several bacteria and a few basidiomycetous
yeasts.
The phylloplane antagonists, Trichoderma harzianum, T. viride and
Penicillium oxalicum were found to readily parasitise R. solani hyphae
leading to coiling, penetration followed by disintegration and death of the
mycohost.
When these antagonists were cultured on bran and tried for their
efficacy as potential biocontrol agents of R. solani, it was found that these
fungi could significantly reduce the incidence and intensity of sheath blight of
rice, though this was not comparable with the effect of the fungicide carboxin.
