Studies on infection of certain paddy varieties by pyricularia oryzae cav and its control

Abstract

(1) Collection of infected samples of rice plants was made from major rice growing areas of old Sibsagar district, viz., Nazira, Teok, Dergaon, Karangaon, Joysagar, Jhanji, Titabar in the year 1985. The varieties of rice included were Joha, Monohar sali, IR8, Pusa, Aijung, Bora and Benibhog. (2) 66 isolates of fungi were obtained from different infected parts, viz., leaves, nodes, panicles and grains of rice plants and the fungus Pyricularia oryzae Cav. was found to be responsible for this disease of rice plants which was found widely prevalent in all these seven localities. Strain differentiation was made basing on morphological and physiological characters and also on degree of virulence. 4 different strains of Pyricularia oryzae Cav., viz., quotAsquot, quotBsquot, quotCsquot and quotDsquot were obtained but only 3 strains (Bs, Cs and Ds) showed sufficient virulence. The strain quotDsquot was found to be the most virulent among them, whereas the strain, quotAsquot was found to be the least virulent. (3) Test of resistance was carried out with 7 varieties of rice of which quotPankajquot was found to be the most resistant. The variety quotSaketquot was found to be the most susceptible against Pyricularia oryzae Cav. (4) Study on fungai physiology of the virulent strains showed variation in growth characters in different nutrients and host extract media. Among the solid media the host extract agar medium provides as the best medium for growth and sporulation. Among the synthetic media, Czapek dox liquid medium was found to be the most favourable for growth and sporulation. Among the synthetic and non-synthetic media, the best was found to be the non-synthetic medium (Rice powder agar medium). On the other hand, among the synthetic medium, quotmedium Equot (glucose, KH2PO4, MgSO4, Asparagine, thiamine hydrochloride, Biotin and double distilled H2O) showed the maximum vegetative growth and sporulation. (5) Evidences also showed that external stimuli, viz., temperature, pH, relative humidity had much influence on growth and sporulation of these strains of Pyricularia...