Inoculation Techniques for Identifying Resistance in Sorghum Genotypes to Sorghum Ergot
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Seven inoculation methods were tested at multiple field sites with different climates in Texas and Mexico to determine the technique most suitable for routine screening of sorghum (Sorghum bicolor (L.) Moench) germplasm for resistance to Claviceps africana (causal agent of sorghum ergot). A single spray or sponge inoculation before flower initiation followed by bagging of the panicles for seven days was the most reliable technique for identifying ergot-resistant sorghum genotypes. This method ensures that unfertilized ovules and infection sites were exposed to the pathogen at the time of greatest vulnerability, thereby reducing the influence of flowering characteristics. This method is repeatable and rapid, thus providing a useful procedure for germplasm evaluation. Disease symptoms on sorghum genotypes are expressed within a reasonably short period. Compared with the other methods, inoculated and bagged panicles resulted in a significantly higher percentage of ergot-infected florets in all environments. Across sorghum lines, no significant increases in ergot severity were observed between inoculated nonbagged, inoculated and misted, and water-sprayed control panicles. In all environments, percent ergot severity per panicle across treatments generally increased from 10 to 15 days after inoculation with negligible increases in disease severity after 15 days. This suggests that ergot assessments after inoculation can be concluded within 15 days. None of the genotypes tested was completely resistant to sorghum ergot. However, NC+8R18, NC+7W97, and the two sister-lines of IS8525 (IS8525J and IS8525D) exhibited more resistance to ergot than the other sorghum lines tested. 2005 by The Haworth Press, Inc. All rights reserved.
