Effect of plant protection chemicals on foliar pathogens and Phylloplane microflora of rice

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.