Potato Progress

Volume 22 Number 2

‍Potato Fusarium dry rot pathogen diversity in the Northwest

Christy L. Christian and Kasia M. Duellman

University of Idaho – Idaho Falls Research & Extension Center

Corresponding author contact information: Kasia M. Duellman (kduellman@uidaho.edu)

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Introduction

Fusarium dry rot of potato is a fungal disease of tubers that can develop in storage. When the disease occurs during seed preparation or after planting, it is commonly called Fusarium seed decay. Several different species in the genus Fusarium can cause the disease. Though most potato varieties are susceptible to infection, the degree of susceptibility may differ among potato varieties. The most reliable management strategy is to minimize wounds any time potatoes are handled. Commercially available fungicide seed potato treatments also effectively minimize disease. 

The information presented here is one outcome of research sponsored by the Northwest Potato Research Consortium and the Idaho Potato Commission. It highlights the importance of knowing which dry rot pathogen is predominant in a potato production operation and how this information can help inform potato variety selection.

‍Pathogen diversity

In the Northwest, a recent survey with collaborators from University of Idaho, Oregon State University, and Washington State University showed that Fusarium sambucinum and Fusarium oxysporum were the two most prevalent species associated with Fusarium dry rot in the region. Other species found in the region that were shown to cause dry rot include F. avenaceum, F. cerealis, F. culmorum, F. graminearum, and F. redolens, among others (Table 1). The different species that cause dry rot can look very different when they are in pure culture (Figure 1). Laboratory tests can determine which pathogen is causing dry rot.

‍Potato varieties and their relative susceptibility to different Fusarium dry rot pathogens

To demonstrate how potato varieties may vary in their response to Fusarium dry rot, we challenged seven different potato varieties with four different species of Fusarium (Table 2). We found that Fusarium sambucinum generally produced larger lesions on most of the potato varieties we tested, forming the typical dry, crumbly dark brown phase of the disease (Figure 2). The isolate of Fusarium oxysporum that we used was most aggressive on the variety ‘Dark Red Norland’ compared to the other six potato varieties (Figure 3).  

‍Fusarium oxysporum usually showed the “wet phase” of the disease, where the lesion, or a portion of it, has not yet dried up, is still firm, and (in this case) is a medium-brown color (Figure 3). The “wet phase” can occur with other species that cause dry rot, and sometimes it appears black or dark brown; it is often considered an early stage of the disease before the lesion dries and takes on the more characteristic crumbly texture. The remaining two types of dry rot pathogens that we tested against the seven potato varieties, Fusarium culmorum and Fusarium redolens, were far less aggressive on all seven potato varieties compared to Fusarium sambucinum and Fusarium oxysporum (Figures 4 and 5). The symptoms of other dry rot pathogens on selected potato varieties are shown in Figures 6-10. 

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