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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)

Location: Vegetable and Forage Crops Production Research

2008 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.


3.Progress Report

Little success has been attained with application of fungicides or other products to controll powdery scab. Severity of powdery scab on roots and tubers treated with Phostrol did not differ significantly (P > 0.05) than those from plants not treated with Phostrol. However, roots and tubers of Shepody from the section of the field treated with Moncut had substantially lower levels of powdery scab than roots and tubers not treated with Moncut. Mean gall index for roots was 1.8 for plants treated with Moncut and 3.3 for the non-treated control. Area of tubers with lesions was 5 % for those treated with Moncut and 9 % for the non-treated control. Incidence of tubers with lesions was 62% from plants treated with Moncut and 85% for the non-treated control. Powdery scab was also substantially less in plots treated with Moncut in a previous test. Moncut may be beneficial in reducing the effects of powdery scab on potato in the Columbia Basin.

The influence of tuber and soil-borne inocula of Colletotrichum coccodes on black dot severity was studied in four consecutive years in the greenhouse. Potato tubers were either inoculated or not inoculated with a conidial suspension of C. coccodes, and were grown in soil infested or not infested with sclerotia. Sclerotial densities on roots and crowns, and sclerotial height on stem were greater (P<0.05) on potatoes grown in infested soil or from infected tubers in infested soil than on potatoes grown from infected tubers, or from non-inoculated control plants in three of four years. More (P<0.05) progeny tubers were infected with C. coccodes when plants were grown from infected tubers in non-infested soil than when plants were grown in infested soil in only one of three years. Total yield in two of four trials was significantly (P<0.05) or notably (P=0.059) lower when plants were grown in infested soil from infected or non-infected tubers than when plants were grown in non-infested soil from infected tubers. The influence of soil-borne inoculum concentrations of 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 levels of damage. This research falls within NP 301 Component 3: Genetic Improvement of Crops. 3c: Germplasm Enhancement/Release of Improved Genetic Resources.

Oversight of the Specific Cooperative Agreement was carried out by telephone conversations, in-person meetings, and sharing of data by email between the ADODOR and Washington State University's lead researcher.


Last Modified: 7/25/2014
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