Update on sugarcane aphid genetics, management in sweet sorghum, and breeding for resistance

Authors: Knoll, Joseph - Joe; Harris-Shultz, Karen; Ni, Xinzhi

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 4/2/2019
Publication Date: 10/21/2019
Citation: Knoll, J.E., Harris-Shultz, K.R., Ni, X. 2019. Update on sugarcane aphid genetics, management in sweet sorghum, and breeding for resistance. In: Lima, I., Eggleston, G, and Clayton, C. (eds.) Advances in Sugar Crops Processing and Conversion, May 15-18, 2018, New Orleans, LA. pp. 172-186.

Interpretive Summary: Since 2013 the sugarcane aphid (Melanaphis sacchari) has become a significant pest of all types of sorghum in the United States. Because sweet sorghum is used to produce an edible syrup, very few pesticides are labeled for use on this crop, so alternative strategies are needed to manage sugarcane aphids in sweet sorghum. This paper highlights some of the recent research carried out by the USDA-ARS at Tifton, GA as part of the sugarcane aphid Areawide Pest Management project, as it pertains to sweet sorghum. Each year since 2015, sugarcane aphids were collected from across the southern states. Their DNA was analyzed in order to monitor their genetic diversity. The sugarcane aphids infesting sorghum and Johnsongrass (a weedy relative of sorghum) in the United States were found to be largely genetically identical, constituting what is known as a ‘superclone.’ Although sugarcane aphids have been an occasional pest of sugarcane in Louisiana and Florida for many years, this superclone has not been observed in North America prior to the outbreak on sorghum in 2013. Because sugarcane aphids must migrate north each year to infest sorghum, a planting date study was conducted to determine if cultural practices, such as late or early planting, could minimize sugarcane aphid damage in sweet sorghum in Tifton. For three years, sweet sorghum was planted in April, May, and June within the same field. Sugarcane aphids arrived in mid-late June and built to very high numbers in the first two plantings, until the population ‘crashed’ apparently due to naturally occurring fungal disease. The third planting thus escaped major damage. We observed this same result all three years, which suggests this could be exploited for managing sugarcane aphid in small sweet sorghum fields. Further study is needed to determine the causal fungus and to determine the conditions which trigger an aphid population collapse. Our long-term strategy is to develop new sweet sorghum cultivars with genetic resistance to the sugarcane aphid. Several sources of resistance have been identified, and efforts to breed sugarcane aphid resistant sweet sorghum are continuing.

Technical Abstract: Since 2013 the sugarcane aphid (Melanaphis sacchari) has become a significant pest of all types of sorghum in the United States. Options for controlling this insect with pesticides are very limited for sweet sorghum producers. This paper highlights some of the recent research carried out by the USDA-ARS at Tifton, GA as part of the sugarcane aphid Areawide Pest Management project, as it pertains to sweet sorghum. Monitoring of the genetic diversity of the sugarcane aphid population in the United States has been completed each year since 2015. The sugarcane aphids infesting sorghum and Johnsongrass in the United States were found to be largely genetically identical, and thus constitute a superclone. Because sugarcane aphids must usually migrate northerly each year, a planting date study was conducted to determine if cultural practices, such as late or early planting, could minimize sugarcane aphid damage in sweet sorghum in Tifton. Sorghum was planted in April, May, or June within the same field. Sugarcane aphids arrived in mid-late June, and built to very high numbers in the first two plantings, until the population ‘crashed’ apparently due to naturally occurring epizootics of entomopathogens. The third planting thus escaped major damage. We have observed this same result for three years, which suggests this could be exploited for managing sugarcane aphid in small sweet sorghum fields. Our long-term strategy is to develop new sweet sorghum cultivars with genetic resistance to the sugarcane aphid. Several sources of resistance have been identified, and efforts to breed sugarcane aphid resistant sweet sorghum are continuing.