Submitted to: Journal of New Seeds
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/15/2004
Publication Date: 5/5/2005
Citation: Prom, L.K., Erpelding, J.E., Isakeit, T., Montes, N. 2005. Inoculation techniques for identifying resistance in sorghum genotypes to sorghum ergot. Journal of New Seeds. 7(1):9-22. Interpretive Summary: In the United States, sorghum ergot, a new disease, poses a serious threat to sorghum production, especially in hybrid seed production fields. The disease causes major losses in yield and grain quality. The best method for controlling the disease is the use of resistant lines. Currently, there are no resistant sorghum lines, and this may be due to the lack of a suitable method that can be used to identify good resistant sources. Therefore, this study was conducted to identify the best method of inoculation that can be routinely used for screening sorghum lines for ergot resistance. Our studies have shown that spray or sponge inoculation followed by bagging the sorghum seed heads for 7 days is the best method for identifying ergot resistant sorghum lines. This method was shown to be reliable in different locations in Texas and Mexico. In addition, by using this method, results can be obtained in 10 to 15 days after treatment of the sorghum plants. Spray and sponge inoculation followed by bagging of the sorghum seed heads can now be used to identify sorghum lines that are resistant to ergot. This in turn will lead to higher yields and profits for growers in the United States.
Technical Abstract: Seven artificial 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 germplasm for resistance to Claviceps africana (causal agent of sorghum ergot). The results indicate that a single spray or sponge inoculation before anthesis 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 are 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 to 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 increased from 10 to 15 days after inoculation with negligible increases in disease severity after 15 days. This suggests that ergot assessments after artificial inoculation can be concluded within 15 days. Non of the genotypes tested were completely resistant to sorghum ergot. However, NC+8R18, NC+7W97, and the two sister-lines of IS8525 (IS8525J and IS8525D) were more tolerant to ergot than the other sorghum lines tested.