2013 Annual Report
1a.Objectives (from AD-416):
1. Identify or develop tolerant germplasm lines, study the inheritance of tolerance, and utilize genetic differences in herbicide tolerance to improve crop safety and enhance weed management in watermelons and sweetpotato.
2. Develop vegetable crop production systems that utilize competitive crop genotypes and innovative cultural practices to reduce the impact of weeds.
1b.Approach (from AD-416):
Develop watermelon germplasm lines with enhanced tolerance to clomazone herbicide using a conventional plant breeding strategy, study the inheritance of clomazone tolerance, and identify or develop tolerant lines for use in watermelon breeding and as rootstocks for grafted watermelon production. Assess watermelon germplasm for differences in halosulfuron methyl tolerance, and investigate the feasibility of developing tolerant cultivars using conventional plant breeding approaches. Identify sweetpotato clones that differ in clomazone and flumioxazin tolerance, use a recurrent mass selection breeding approach to generate clones with high levels of tolerance and good horticultural characteristics, and make them available for use by sweetpotato breeders. Assess the competitive advantage against weeds of sweetpotato genotypes with more vigorous growth habits in comparison to less competitive conventional cultivars, identify competitive genotypes with good horticultural quality, and evaluate them as component in integrated weed management systems for conventional and organic growers. Evaluate weed management practices utilizing competitive southernpea cultivars as a component in integrated weed management systems for conventional and organic growers. Investigate the impact of poultry and swine litter biochar soil amendment on southernpea and weed growth and on herbicide activity.
A greenhouse study to determine the inheritance of clomazone tolerance in wild watermelon lines was completed; preliminary assessment of the data suggests that tolerance is a dominant trait and may be influenced by maternal genes; wild watermelon lines with genetically uniform clomazone tolerance were developed using recurrent selection, and greenhouse and field trials were conducted to confirm their high levels of tolerance. A backcross breeding project to transfer clomazone tolerance from citron melon into watermelon cultivars was continued. Halosulfuron methyl tolerant watermelon lines selected in a field screening experiment were re-evaluated for tolerance in a greenhouse experiment. A greenhouse experiment was used to identify clomazone tolerant sweetpotato seedlings derived from a crossing block last year. Nine lines selected from the experiment were included in a crossing block set up to generate highly tolerant plants for the next cycle to breed sweetpotato lines with increased tolerance. A field experiment was completed to determine the competitiveness of 13 sweetpotato lines against weeds. A field experiment to assess the competitiveness of determinate, semi-determinate and non-determinate cowpea varieties against weeds and their response to weed interference was completed. A field investigation was conducted in collaboration with the location nematologist to determine the effect of nematode resistant and susceptible cover crop cowpea varieties on nematodes and weeds in subsequent rotational crops. Field and greenhouse experiments to assess clomazone tolerance in a collection of 46 broccoli varieties were completed. Most of the varieties were adequately tolerant to allow safe use of the herbicide.
Broccoli varieties were shown to be tolerant to clomazone herbicide. Clomazone herbicide is registered for use in cabbage, and a petition for broccoli registration has been submitted to the Environmental Protection Agency by the specialty crops pesticide registration project (IR-4) because the herbicide is needed to supplement weed management options for the expanding eastern U.S. broccoli production. ARS researchers at Charleston, SC, compared the relative tolerance of broccoli and cabbage cultivars to assure that broccoli tolerance is adequate for safe use of the herbicide. A secondary objective was to identify susceptible varieties that can be avoided so that crop loss caused by clomazone injury can be minimized. Initial field and greenhouse studies demonstrated that the range in tolerance was comparable for the two crop types. Subsequently, 46 broccoli varieties were evaluated for tolerance in field and greenhouse experiments. None of the broccoli varieties were more susceptible than the most susceptible cabbage variety; however, two varieties showed greater sensitivity than others indicating that clomazone should be used cautiously if the tolerance of the variety planted is not known. This research demonstrates that the tolerance of most broccoli cultivars is adequate to safely use clomazone for weed management; this information will be very useful to broccoli producers hoping to make use of this herbicide.
Harrison Jr, H.F., Farnham, M.W. 2013. Differences in tolerance of broccoli and cabbage cultivars to clomazone herbicide. HortTechnology. 23(1):6-11.