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Title: Identification of citrullus lanatus germplasm lines tolerant to clomazone herbicide

item Harrison Jr, Howard
item Kousik, Chandrasekar - Shaker
item Levi, Amnon

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2011
Publication Date: 5/1/2011
Citation: Harrison Jr, H.F., Kousik, C.S., Levi, A. 2011. Identification of citrullus lanatus germplasm lines tolerant to clomazone herbicide. HortScience. 46(5):684-687.

Interpretive Summary: Command 3ME herbicide (clomazone) controls a number of annual grass and broadleaf weeds that are important pests in watermelon fields and is used extensively by watermelon growers. However, watermelons are not highly tolerant to the herbicide, and it may cause damage to the crop. As a result, recommended clomazone use rates are lower for watermelon than for other crops. The objective of this study was to search for watermelon lines that are more tolerant to clomazone. A genetically diverse collection of watermelon varieties and lines was evaluated in greenhouse and field studies to determine for tolerance to clomazone. Two wild watermelon lines from Africa, PI 500354 and PI 482324, were highly tolerant to clomazone in all studies. These lines may be useful in watermelon breeding to increase the tolerance of commercial watermelon varieties. Clomazone tolerant varieties would allow growers to use the herbicide more effectively and reduce the risk of injury to the crop.

Technical Abstract: Clomazone herbicide is registered for use in watermelon; however, crop tolerance is marginal and the recommended use rates (0.07 to 0.1 kg ai ha-1) are lower for watermelon than for some other crops. In a greenhouse germplasm evaluation experiment including 56 germplasm accessions and watermelon cultivars, three Citrullus lanatus var. citroides plant introduction accessions (PI 482324, PI 5003540 and PI 532624) were not injured by clomazone; whereas, most of the other lines were moderately or severely injured. A greenhouse concentration response curve experiment demonstrated that the clomazone concentration required to cause moderate injury or growth reduction to the highly tolerant PI 500354 was approximately three to five times the concentration that caused similar injury to the susceptible PI 244017. Subsequent field experiments demonstrated that two tolerant accessions (PI 500354 and PI 482324) were injured less by clomazone and recovered more rapidly from clomazone injury than two susceptible accessions (PI 244017 and PI 271773) and two watermelon cultivars (Charleston Gray and Crimson Sweet). Tolerant germplasm lines like PI 482324 and PI 500354 may be useful as sources of clomazone tolerance in watermelon breeding.