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Title: Citrullus Germplasm Lines Vary in Clomazone Herbicide Tolerance

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

Submitted to: Cucurbitaceae Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/5/2010
Publication Date: 10/14/2010
Citation: Harrison Jr, H.F., Kousik, C.S., Levi, A. 2010. Citrullus Germplasm Lines Vary in Clomazone Herbicide Tolerance. Cucurbitaceae Proceedings. p. 31-34.

Interpretive Summary: N/A

Technical Abstract: Differences between Citrullus germplasm lines in clomazone injury were first observed when the herbicide was used for weed control in fields containing germplasm lines of watermelon breeding project at the U.S. Vegetable Laboratory, Charleston, SC. The objectives of this investigation were to assess clomazone tolerance in a collection of Citrullus germplasm and quantify differences in tolerance between susceptible and tolerant accessions. An initial greenhouse screening experiment evaluated 123 Citrullus accessions. Most accessions were moderately or severely injured by clomazone at 1.5 mg/kg potting medium. Three Citrullus lanatus var. citroides accessions (PI 482319, PI 482324, and PI 500354) were not injured by clomazone in the screening experiment. Other citroides accessions were severely injured. Variability among individual plants within some accessions (apparent genetic segregation) also was observed. A second greenhouse experiment was used to establish concentration response curves for the tolerant citroides accession PI 500354, the susceptible citroides accession PI 244017, and the inbred watermelon cultivar Charleston Gray. Regression analysis of the data from the greenhouse response curve experiment indicated that the concentrations that caused a 30% reduction in shoot weight were approximately 1.2, 3.0, and 6.2 mg/kg for PI 244017, Charleston Gray and PI 500354, respectively. The concentrations that caused a moderate injury rating of 3 were 1.0, 1.4, and 3.1 mg/kg for PI 244017, Charleston Gray, and PI 500354, respectively. The clomazone tolerance of PI 500354 in comparison to PI 244017 and Charleston Gray was confirmed in a field experiment. PI 500354 exhibited moderate injury and recovered rapidly from post-transplanting application of clomazone at 0.26 kg/ha in the field. PI 244017 and Charleston Gray plants were severely injured or killed by this treatment which is almost four times the recommended rate for watermelons on sandy soils.