Brown spot disease of rice in Egypt
1989
El-Kazzas, M.K. | Osman, Z.H. (Tanta Univ., Kafr- El- Sheikh (Egypt). Faculty of Agriculture)
The most conspicuous symptom of brown spot disease in rice is brown oval spots with grey centers on leaves and glumen. Neck and uppermost internodes are also blighted, but symptoms resemble neck rot infection caused by blast fungus. Various aspects of the disease were studied, including yield loss as related to stage of infection, influence of environmental factors on disease development, and interaction between blast and brown spot pathogens. Artificial inoculation of rice plants with Cochliobolus miyabeanus, the causal organism, at flowering and milky stages reduced yield the most, but almost no yield reduction was observed from inoculation at maturity stage. Relative humidity, dew period, and number of trapped spores showed positive correlation with disease development. Means of day-night relative humidity as well as daytime trapped spores appeared to be closely associated with disease development. Disease incidence significantly increased on both leaves and grain when plants were not supplied with nitrogen fertilizer, compared with plants that received 40 or 80 kg N/feddan. The rate of 40 kg N/feddan was optimal, giving the lowest disease index and highest grain yield. Neither phosphorus (at 0 and 15 kg P/feddan) nor potassium (at 0 and 24 kg/feddan) showed any effect either on disease development or grain yield. A study of the interaction between H. oryzae and P. oryzae revealed that the lowest number of blast lesions after 48 h was induced on seedlings preinoculated with H. oryzae, rather than with P. oryzae. Brown spots decreased with prolonged time between successive inoculations up to 6d. Inoculation with a mixture of H. oryzae and P. oryzae significantly decreased the number of blast lesions, brown spot was not influenced at all.
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