Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: February 23, 2010
Publication Date: April 1, 2010
Citation: Harrison Jr, H.F., Kousik, C.S., Levi, A. 2010. Tolerance to the Herbicide Clomazone in Watermelon Plant Introductions. HortScience. 45:510. Technical Abstract: The pre-emergence herbicide clomazone (trade name: Command 3ME), is widely used in watermelon production in the US for suppression of annual grasses and broadleaf weeds growing in between plastic beds. Exposure of young watermelon plants to clomazone can cause moderate or severe injury that is expressed as bleaching of leaves and growing tips. Even moderate injury results in delayed growth and development. Most commercial watermelon varieties are susceptible to clomazone injury. The objectives of the current study were to determine if clomazone tolerance could be identified in watermelon plant introductions (PI). We initially evaluated 123 PI’s and identified several that were tolerant to clomazone. The tolerant PI’s were not injured by clomazone at 1.5 mg ai/kg dry soil. Watermelon cultivars were moderately or severely injured by this concentration. Based on the initial screen; 67 PI’s were selected for reevaluation. Twelve were rated <2 on a 1-10 rating scale (1=no injury, 10=plant dead). Of these, three Citrullus lanatus var. citroides PI’s (PI 482324, PI500354, PI532624) were not injured. PI271773 and PI244017 (C. lanatus var. citroides) and the variety Charleston Gray were very susceptible to clomazone injury. Variability among individual plants within PI’s was also observed. In a subsequent concentration response experiment, PI482324 and PI500354 were injured less at 3 mg a.i/kg dry soil; than PI244017 and Charleston Grey were injured more at 0.75 mg/kg. Two field experiments further confirmed the tolerance of PI500354 and PI482324 to clomazone (1.5 pt/acre, 0.5 lb a.i.) compared to the susceptible lines PI271773, PI244017, and Charleston Grey which were significantly more injured. We have selfed (S3) the most tolerant or susceptible plants selected from these PI’s in order to obtain genetically homogenous lines for genetic studies.