Project Number: 5348-21000-026-01
Project Type: Specific Cooperative Agreement

Start Date: Sep 17, 2007
End Date: Jan 31, 2009

Objective:
Management approaches to limit damage and/or control bacterial wilt have relied upon crop rotation, certified seed, seed treatment with an antibiotic like streptomycin, and the use of resistant cultivars. Unfortunately, since the 1970s, breeding improvement programs have not continued to include bacterial wilt when it was virtually eliminated by the widespread use of resistant cultivars developed for regions where the disease has been a serious threat. During the last 30 years, the disease has not posed a threat to major bean production areas until its recent resurgence. Reasons for this resurgence could include contaminated seed sources, long-term survival of the pathogen on other susceptible hosts including weeds, pathogenic changes in related strains that were presumed to be host-specific (e.g., sugarbeet), and the apparent lack of resistance in most cultivars in market types such as great northern, yellow, pinto, navy, black and light red kidney that have been released for commercial production during the last 20 to 30 years. Research is urgently needed to identify sources of genetic resistance against recent strains of the bacterium to provide breeders with options for the improvement of future cultivars and to make recommendations to producers in areas where bacterial wilt is a problem.

Approach:
Inoculation Procedure ¿ Specific yellow and orange isolates will be selected later this fall by H. Schwartz after completion of ongoing pathogenicity comparisons of a subset of nearly 100 isolates made from various market types of beans in Nebraska and Colorado during 2004-2006. Hsieh et al. (2005) recently evaluated Canadian cultivars and breeding lines for resistance to a yellow and orange variant of bacterial wilt, and observed reaction differences between entries. Recent workers have not found a purple isolate as reported in 1967 by Schuster and Sayre (1967); and we do not have access to a purple isolate at this time. The accessions and other candidate germplasm will be screened using the cotyledonary node inoculation method of Rickard and Walker (1965). Seven to 8 seeds will be sown 2.5 cm deep into potting mix in a 15-cm wide plastic pot and thinned to 5 emerged seedlings prior to inoculation. The point of a sterile dissecting needle bearing inoculum will be inserted into the stem at the cotyledonary node of 7 to 10 day old seedlings. The inoculated plants and checks (susceptible US 1140 or UI 59 and resistant Emerson or Star, depending upon seed availability of these older materials) will be incubated in a greenhouse with a daily temperature of 28oC/ 22oC - 16 hr day/8 hr night photoperiod with watering as needed. Statistical Protocol ¿ Two pots of 5 plants each will serve as 1 of 3 replicates for inoculation individually with the yellow or orange isolate of Bacterial Wilt. Ten plants each of a resistant check (e.g., Emerson or Star) and susceptible check (e.g., US 1140 or UI 59) will be included with each two month-long series which will consist of one Bacterial Wilt isolate, approximately 100 entries, each with 3 reps, taken from planting to emergence to inoculation to final evaluation 4 weeks later. Approximately 200 entries will be evaluated over a 4-6 month period per isolate; requiring a total of 9-12 months to evaluate all entries for reactions to both Bacterial Wilt isolates. Disease Evaluation ¿ Disease development will then be recorded weekly (1, 2, 3 and 4 weeks post inoculation) according to a modification of Hseih et al. (2005): 1 = no wilt or discoloration, 2 = wilt or discoloration on one of the primary leaves, 3 = wilt or discoloration on both primary leaves with no symptoms on the 1st trifoliolate leaf, and 4 = wilt or discoloration on the 1st trifoliolate leaf. Data will be reported as an average severity for the 10 plants per rep. Documents SCA with Colorado State University. Formerly 5348-21000-020-15S(5/08).