Determining the Host-range and Developing Seed-treatment for Managing Bacterial Spot on Pumpkin

Determining the Host-range and Developing Seed-treatment for Managing Bacterial Spot on Pumpkin

Summary

Pumpkin is a high-value crop grown throughout the United States (US). Approximately 1.5 billion pounds of pumpkins are produced in the US every year and Illinois with about 25,000 acres ranks first in pumpkin production in the US. More than 90% of processing pumpkin are grown and processed in Illinois. Bacterial spot, caused by Xanthomonas cucurbitae has become one of the most economically important diseases on pumpkins and a serious threat to the industry. Leaf spots and fruit lesions and rot are major symptoms of this disease, causing up to more than 75% yield losses. In the past five years, the disease has become more prevalent in Illinois and other Midwestern states and many growers complain about the yield losses and of lack of effective disease management measures. Developing effective management of bacterial spot of pumpkin has not been feasible because of lack of sufficient information on the etiology of the disease, especially on the host-range and seed-borne aspect of the pathogen. This is proposal for a two-year project to generate necessary information on the etiology of bacterial spot of pumpkin and develop effective methods for management of the disease. The specific objectives of this research are to: (1) identify the host-range of X. cucurbitae; (2) determine the importance of seed-borne aspect of the pathogen; and (3) develop management of the disease, emphasizing effective seed-treatments and cropping rotations. Result of this study will be presented to growers, industry personnel, extension educators, students, and scientists at the local, statewide, regional, and national meetings. The results also will be published in the newsletters, websites and refereed-journals.

Objectives/Performance Targets

This is proposal for a two-year project to generate necessary information on the etiology of bacterial spot of pumpkin and develop effective methods for management of the disease. The specific objectives of this research are to: (1) identify the host-range of X. cucurbitae; (2) determine the importance of seed-borne aspect of the pathogen; and (3) develop management of the disease, emphasizing effective seed-treatments and cropping rotations.

Accomplishments/Milestones

This study assessed host range of X. cucurbitae. Fifty plant species, including crops and weeds, in the families Amaranthaceae, Brassicaceae, Chenopodiaceae, Cucurbitaceae, Gramineae, Leguminosae, Liliaceae, Malvaceae, Purtulaceae, Solanaceae, and Umbelliferae were tested in a greenhouse for their susceptibility to X. cucurbitae. Bacterial suspensions were prepared from 3-day old X. cucurbitae cultured on Luria-Bertani (LB). Leaves of 3- to 4-week old plants were inoculated with 108 CFU/ml bacterial suspensions. Inoculated plants were maintained in a greenhouse at 24-28°C for up to 30 days. Development of symptoms (water-soaked and necrotic lesions) on the leaves was recorded daily. Also, cucumber fruit were inoculated by spraying the bacterial suspension (108 CFU/ml) onto the fruit. All of the plant species in Cucurbitaceae family developed symptoms and X. cucurbitae was isolated from the lesions 20 days after inoculations. None of the species from other plant families developed symptoms. In another study, susceptibility of 89 USDA accessions of pumpkin and squash (Cucurbitae pepo) to X. cucurbitae was assessed in a greenhouse. There was significant (P = 0.001) difference in disease severity of leaves among the accessions. In 2012, nine USDA accessions and 17 commercially grown cultivars of pumpkin were tested for their susceptibility to X. cucurbitae in an irrigated field. Seeds were sown on 18 May, in a greenhouse and 18-day-old seedlings were transplanted on 6 June. A mixture of bacterial suspensions (108 CFU/ml) of five isolates of X. cucurbitae was sprayed onto leaves on 31 July (at vining growth stage). Another spray-inoculation with a bacterial suspension (108 CFU/ml) of five isolates of X. cucurbitae onto leaves and fruit was carried out on 24 August (at fruit ripening). Severity of bacterial lesions on leaves was assessed on 10 August (10 days after the first inoculation) and on fruit on 7 September (2 weeks after the second inoculation). Disease severity on leaves was significantly (P = 0.001) different among the accessions and cultivars tested. Disease severity on fruit was not significantly (P = 0.1) different among the accessions and cultivars.

Impacts and Contributions/Outcomes

Now, we know the host-range of Xanthomonas cucurbitae. After determining survival of the pathogen in the field, we will be able to have effective crop rotation for management of bacterial spot of pumpkin.