Fusarium and Verticillium Wilts in Potato

Fusarium and Verticillium Wilts are common in most potato production areas; Verticillium wilt is more likely to cause serious reductions in tuber size and yield. Species of Fusarium also cause dry rot, an important post-harvest disease of potato.

Vascular wilts are characterized by leaf yellowing, often in a one-sided manner that proceeds up the stem. Before wilting, upper leaves have a light, green to grey appearance. Leaf yellowing, necrosis, flagging, and stem death follow. The vascular (water conducting) system exhibits a brown discoloration. Fusarium dry rot occurs at wound sites as shallow brown lesions which enlarge and wrinkle in concentric rings. The underlying tissue becomes desiccated and brown. Dry rot lesions may be invaded by soft-rotting bacteria.

Verticillium Wilt is caused by one of two soilborne fungi-V. dahliae and V. albo-atrum. V. dahliae prefers warmer temperatures and survives by the production of microsclerotia, while V. albo-atrum produces dark, resting mycelia. The two pathogens can be introduced into new fields, by wind, the movement of soil on equipment, and on infected seed tubers. They can persist in the soil for 5-10 years in the absence of a susceptible host and have wide host ranges. Verticillium Wilt can interact with other pathogens such as plant parasitic nematodes, bacteria, or other fungi to cause increased losses to disease.

Three species of Fusarium can cause wilt disease on potato- F. avanaceum, F. oxysporum, and F. solani f. sp. eumartii.  The predominant species will vary with region. The pathogens are soilborne and can persist there for several years. Dry rot is caused by F. solani and F. sambucinum. Sources of inoculum are contaminated seed tubers and infested soil. Fusarium species are often spread during cutting and planting due to the large number of spores liberated from infected tubers. Wounds caused by insects, rodents, and other diseases are subject to dry rot and dry rot also is spread during harvest.

Management:

• Plant resistant or tolerant cultivars. No potato cultivars are immune.
• Avoid injury to tubers and provide conditions that promote wound healing before storage.
• Post harvest applications of registered fungicides can provide disease control in storage.
• Start with disease-free seed tubers or treat seed with registered fungicides.
• Plant when soil moisture and temperature are favorable for rapid growth and emergence.
• Provide adequate nitrogen, phosphorous, and potassium.
• Avoid moisture stress or overwatering.
• Practice long crop rotations to reduce soil populations of the pathogens.
• Incorporation of green manures has shown some promise in reducing losses due to Verticillium Wilt.
• Soil fumigation can provide disease control but treatments are costly and require specialized equipment and technical expertise. Populations of these pathogens quickly return to pre-fumigation levels.