Virulence of corn rust (Puccina polysora Underw.) on maize cultivars
1989
Sutathip Sangkul
Germinability was best maintaining at 25 deg C. The germination percentage of uredospores on 1 % water agar was at higher level than that of Czapek agar. Germination rates on both water and Czapek agar were similar as they dropped rapidly at 30 deg C. A detached leaves method for producting germ tube of corn rust. The germinability was determined by whole leaves clearing method and performed best maintained at 25 deg C and the uredospore germ tube of P. polysora penetrated directly through the host cell surface only in susceptible cultivars, but no developing of pustule formation could by clearly seen. The detached leaves method was suitable for several host plants, its application for seedling maize leave was still not effective resulting from the leave, it did not retard senescence for longer incubation period and the germ tube formation on the maize leave was not shown so clearly as on the slide culture. The lowest concentration of infection level was 100,000 spore/ml. The temperature at 25 deg C and the pustules of P. polysora were produced apparently within 9-10 days after inoculation. After the temperature was increased up to 30 deg C, the infection intensity of corn rust of seedling maize cultivars showed decreasing of pustule numbers since the higher temperature could prevent or greatly reduce infection and survival of corn rust uredospores. Investigations on the morphology of uredospore on infected seedling maize by scanning electron microscope appeared that their characteristics were similar to those of uredospores in nature field. Southern corn rust in late season rather than those in early rainy season, but they still had low infection in dry season. Their symptoms appeared at a lower leaves under wind direction and the late-planted corn had been more severly infected.
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