Among six isolates of Ustilago maydis from different localities, the Beni-Sueif isolate was the most virulent pathogenic followed by isolates of Qalubiya, Fayoum, Gharbiya, Giza and Kafr El-Sheikh. Pathogenicity of an isolate seems to be correlated with germinability of its teliospores. Sporidia caused higher disease severity than teliospores.
Cultivation of garlic, sugar beet, oat, lupine, faba bean or lentil in pots caused considerable decline in viability of teliospore or buried in soil. Root exudates of these plants exhibited similar effect in vitro. The chickpea, barley and wheat as well as their root exudates caused the lowest suppressive effect on viability of teliospores. Viability of teliospores was decreased to some extent when kept for 4-5 months in fallow irrigated or non-irrigated soils.
The reaction of tested maize accessions against artificial infection with common smut was considerably variable. The maize accession TWC-Baraka was the most resistant during 1998 and 1999 seasons followed by the accessions TWC-322 and the SC-129 meanwhile, the local varieties Giza-2 and Boushi, and the hybrids TWC.320, TWC.324, TWC.321, and DC Dahab were the most susceptible.
The plant oils eucalyptus, clove, cinnamon, peppermint, and anise at 750 and 1000 ppm and clove and anise oils at 500 ppm caused 100% inhibition of the in vitro fungal growth. The promising effect of these oils at different concentrations gave good results in controlling common smut disease and increasing corn grain yield under stress of artificial infection under greenhouse and field conditions. The best results were obtained when maize plants were injected with oil simultaneously with pathogen inoculation. Spraying plants with plant oils 48 h before or after pathogen inoculation was partially effective.
Additional key word: common smut, U. maydis, isolates, teliospores, viability, root exudates, preceding crops, varietal resistance, disease control.
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