Evaluation of the USDA sweetpotato [Ipomoea batatas (L.) Lam.] germplasm collection for tolerance to the herbicide clomazone

Sweetpotato [Ipomoea batatas (L.) Lam.], is an important food crop worldwide. Weed management is consistently ranked among the top priorities of the sweetpotato industry in the United States (U.S.). Unfortunately, weed management of sweetpotato in the U.S. can be challenging as there are few herbicides labeled for use on the crop. Clomazone is one of the most widely used herbicides on sweetpotato in the U.S. and is effective in controlling several annual broadleaf weed and grass species and there is interest in developing germplasm that is tolerant to the herbicide. There is a lack of information concerning clomazone tolerance for sweetpotato plant introductions (PIs) that are contained within the germplasm collection of the USDA, ARS, Plant Genetic Resources Conservation Unit. The present study evaluated 564 sweetpotato PIs for tolerance to clomazone under a recommended rate in a field plot, with the objective of identifying sources of tolerance to clomazone. Clomazone injury ratings [1 = no chlorosis, 3 = minor chlorosis (< 20% leaf area), 7 = moderate chlorosis (20–50%), 9 = severe chlorosis (> 50%)] of the 564 sweetpotato PIs indicated that the majority (N = 497 PIs) had either no chlorosis or minor damage. There is ample phenotypic diversity for periderm (skin) and stele (flesh) color and dry matter present within the clomazone tolerant PIs. Additionally, there is sufficient genetic diversity present, as 108 PIs have been characterized and assigned to four genetic clusters with another 81 PIs having high levels of mixed ancestry. The results reported here provide critical baseline data for future studies of resistance and practical breeding for tolerance to clomazone.