Developing Effective Treatments for Eradication of Xanthomonas cucurbitae in Pumpkin Seed

View the project final report

• 2015 annual report

Commodities

• Vegetables: cucurbits

Practices

• Pest Management: chemical control

Bacterial spot, caused by Xanthomonas cucurbitae, has become a serious threat to the pumpkin industry in Illinois and other Midwest states of the United States. X. cucurbitae infects leaves and fruits, causing up to 100% yield losses. X. cucurbitae is considered as a seedborne pathogen and planting pathogen-free seed is an important step in management of the disease. This study was conducted to develop a reliable seed treatment to eradicate the pathogen in the seeds. We evaluated hot-water, hydrochloric acid, and sodium hypochlorite for eradication of X. cucurbitae in naturally-infected and artificially-infested pumpkin seeds. Hot-water treatment at 55°C for 15 min and hydrochloric acid treatment at 0.5% concentration for 40 min eradicated X. cucurbitae in pumpkin seeds without any significant adverse effect on either seed germination or seedling vigor.

Introduction:

Bacterial spot, caused by Xanthomonas cucurbitae, has become a serious threat to pumpkin industry in Illinois and other Midwest states of the United States. The pathogen was first reported in 1926 on ‘Hubbard’ squash in New York. Subsequently, the disease was reported in other cucurbit growing areas in Asia, Australia, Europe, and North America on cucumber, pumpkin, squash, and watermelon.

This pathogen can infect both leaves and fruit. Infected leaves develop small, round to angular, and yellow to beige lesions surrounded by a yellow halo. On some pumpkin cultivars, the lesions may appear more angular, similar to the lesions caused by angular leaf spot, caused by Pseudomonas lachrymens. Lesions may coalesce to cover large parts of the leaves. The lesions on fruit begin as small (1-3 mm in diameter), circular, and slightly sunken with a beige center and brown halo. The lesion may reach 10-15 mm in diameter. Infected fruits are colonized by the opportunistic fungi and bacteria, resulting in decay of fruits.

During 2011-2013, field surveys were conducted in Illinois, Indiana, Iowa, Kansas, Michigan, Missouri, Nebraska, Ohio, and Wisconsin to assess incidence and severity of the bacterial spot in pumpkin and squash. During four weeks of the harvest, 111, 132, and 126 fields in 2011, 2012, and 2013, respectively, were visited. Symptomatic fruit were observed in 95 (86%), 117 (89%), and 113 (90%) of the fields visited, with overall 34, 23, and 19% fruit infected, in 2011, 2012 and 2013, respectively. In some of the fields, more than 90% of fruits were affected.

X. cucurbitae is considered as a seedborne pathogen and planting pathogen-free seed is an important step in management of the disease. Seed-borne inoculi plays an important role in spreading seed-borne diseases, especially in long-distances.

The objective of this study was to develop a reliable seed treatment to eradicate Xanthomonas cucurbitae in pumpkin seeds.