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Longevity of Teliospores of Ustilago scitaminea in Soil. J. W. Hoy, Associate Professor, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803. Zheng Jiaxie, L. B. Grelen, and J. P. Geaghan. Former Visiting Scientist, Research Associate, Department of Plant Pathology and Crop Physiology, and Associate Professor, Department of Experimental Statistics, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803. Plant Dis. 77:393-397. Accepted for publication 1 December 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0393.

Longevity of teliospores of Ustilago scitaminea, the causal agent of sugarcane smut, was studied in soils collected from fields with or without a sugarcane cropping history. Few viable spores (1%) were detected after 4 wk in contact with saturated soil, and none were detected after 6 wk. When teliospores were mixed in nonsterile soils adjusted to three moisture levels, the number of viable spores decreased rapidly after 14 wk. Viable spore numbers consistently decreased most rapidly in the wettest soil, but spore longevity was similar for all three moisture levels in each soil. In three experiments, longevity of spores was limited to 79 wk in soils containing moisture. The number of viable spores also decreased rapidly with time in sterile soils with different moisture contents, and longevity was limited to 47 wk. Variation was observed for different spore collections mixed in air-dried soils maintained at ambient relative humidity. When spores mixed in three air-dried soils were kept under desiccation, the percentage of viable spores did not begin to decrease until after 18 wk. Spores from six locations lost viability after being maintained free of soil for 23 wk at ambient relative humidity. In comparison, germination percentages after 23 wk for the same spore collections maintained under desiccation ranged from 17 to 55%. The results indicate that teliospores of U. scitaminea are not long-lived in soil when moisture is present. This represents a limiting factor for the increase of sugarcane smut under subtropical climate conditions in Louisiana, because soilborne inoculum will not persist through the winter and be present when sugarcane is tillering during the spring.