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United States Department of Agriculture

Agricultural Research Service

Research Project: Control of Powdery Scab and Black Dot Through Resistance Breeding and Pathogen Management Strategies (WSU-Johnson)


2010 Annual Report

1a. Objectives (from AD-416)
Screen potato germplasm resistance for resistance to major pests and pathogens. Test management strategies and their interaction with different levels of host resistance.

1b. Approach (from AD-416)
Plant various genotypes of potato in affected fields infested with major pests and pathogens. Score resistance reactions. Where appropriate find linkages between resistance and molecular markers. Test management strategies and study interactions with different levels of resistance in potato breeding lines and cultivars. Documents SCA with WSU. Formerly 5354-21220-002-24S (5/08).

3. Progress Report
The influence of soil-borne inoculum concentrations of Colletotrichum coccodes (C. coccodes) on the severity of black dot was studied in two trials in the greenhouse. The soil was infested with 0, 0.5, 1.7, 5, and 8.3 grams of inoculum per 1-liter. The study supported the hypothesis that soil-borne inoculum of C. coccodes has a higher disease causing potential than tuber-borne inoculum. The study also indicated that soil-borne inoculum of C. coccodes has a low disease threshold. A small level of inoculum in the soil is sufficient to cause high damage. For the purpose of evaluating differences in germplasm with respect to resistance to black dot, a labor saving technique, has been developed. Green stems are cut from the plant and allowed to air dry. During the drying the sclerotia appear and advance up the stem. The distance that the sclerotia reach is negatively correlated with resistance. This trait was also negatively correlated with weight of tubers greater than or equal to 14 ounces. A molecular marker (STS) that was closely linked with root resistance to Columbia root knot nematode may be linked with resistance to black dot fungus. Black dot affected the total root weight in pot tests. Resistant clones had five times the total root mass as the two susceptible cultivars. It was notable that the susceptible cultivars’ root system mostly lacked root laterals, while the resistant clone has abundant laterals. The total measured root length was greater in the resistant clone than in the susceptible cultivars. Oversight of the Specific Cooperative Agreement was carried out by telephone conversations, in-person meetings, and sharing of data by email between the ADODR and Washington State University's lead researcher. This project provides pathology support for the Main CRIS's objectives of determining the genetics of resistance to black dot and powdery scab

4. Accomplishments

Last Modified: 06/24/2017
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