Fusarium spp. Causing Dry Rot of Seed Potato Tubers in Michigan and Their Sensitivity to Fungicides

Abstract

A survey of seed potato tubers in Michigan seed production storage facilities was carried out during 2009 and 2010. Fusarium spp. associated with tuber dry rot symptoms were identified to species and tested for sensitivity to difenoconazole, fludioxonil, and thiabendazole. Symptomatic tubers (n = 370) were collected from a total of 51 seed lots, from which 228 isolates of Fusarium were recovered and identified to 11 species. Fusarium oxysporum was the most commonly isolated species (30.3%), followed by F. equiseti (19.3%). F. sambucinum and F. avenaceum were third most prevalent (each at 13.6%). Less prevalent species (each at 4 to 10%) included F. cerealis, F. solani, and F. acuminatum; and species present at ≤3% included F. sporotrichioides, F. torulosum, F. tricinctum, and F. graminearum. Representative isolates of all species were pathogenic when inoculated onto seed tubers (‘Dark Red Norland’). Isolates of F. sambucinum were the most virulent. All 228 isolates of Fusarium were sensitive to difenoconazole (effective fungicide concentration that caused 50% inhibition of mycelial growth [EC50] < 5 mg/liter). Insensitivity to fludioxonil (EC50 > 100 mg/liter) was detected only for F. sambucinum and F. oxysporum isolates at 8.9 and 20.4%, respectively. All isolates were sensitive to thiabendazole (EC50 < 5 mg/liter), except for those of F. sambucinum (EC50 > 100 mg/liter). Therefore, knowledge of what Fusarium spp. are present in seed potato storage facilities in Michigan may be important if using fludioxonil or thiabendazole for seed piece treatment but not when using difenoconazole.

Diversity of Fusarium spp. associated with dry rot of potato tubers in Poland

“…F. sambucinum was the species most frequently isolated from potato tubers among eight species recovered in 1992-1993 in northeastern USA (Hanson et al 1996), but also more recently in China (Du et al 2012). F. oxysporum was reported to be the primary agent responsible for potato dry rot amidst 11 species in Michigan, USA (Gachango et al 2012) and South Korea (Kim and Lee 1994). F. avenaceum dominated potato Fusarium population investigated between 1997 and 2000 in Scotland (Choiseul et al 2007), while F. solani var.…”

“…Globally, 13 Fusarium species are associated with potato dry rot (Cullen et al 2005). However, this list can be extended to include F. ciliatum, F. reticulatum, F. torulosum and F. verticillioides (Kim and Lee 1994;Choiseul et al 2007;Gachango et al 2012) and most likely is still not complete. The pathogenicities of Fusarium spp.…”

“…in potato tubers either as dry rot agents, secondary pathogens or saprophytes is difficult to estimate, because even within species considered as the dry rot agents, non-pathogenic isolates were found and isolates of different species cause lesions of different sizes, i.e. isolates of F. sambucinum have caused significantly larger lesions than the isolates of other tested species (Gachango et al 2012). In potato dry rot samples, Fusarium isolates that are non-pathogenic to potato in the laboratory assessment are frequently identified (Peters et al 2008a;Peters et al 2008b).…”

Assessment of the Antifungal Activity of Non-pathogenic Potatoassociated Fungi toward Fusarium Species Causing Tuber Dry Rot Disease

“…Nevertheless, besides the problems relative to environmental pollution and chemical toxicity to humans and animals, resistance to Benzimidazole fungicides used for tuber treatment seems to be widespread among strains of Fusarium spp. in the most potato-growing countries including Tunisia [11][12][13]. In Tunisia, azoxystrobin-and fludioxonil-based fungicides had reduced by more than 50% the development of dry rot caused by F. graminearum and F. sambucinum including Benzimidazole-resistant strains [14].…”

“…Strong hyphal lysis, formation of mycelial cords and early production of chlamydospores are the most frequent stress responses exhibited by both pathogens during their in vitro interactions with the potato-associated fungi. Tested as tuber treatment prior to pathogen challenge using a mixed inoculum composed of F. sambucinum and F. solani, 13 isolates out of the 20 tested led to a significant decrease, by 26.9 to 54.8%, in the mean diameter of dry rot lesion, as compared to the inoculated and untreated control. All tuber treatments had significantly decreased mean rot penetration, in comparison to Fusarium spp.-inoculated and untreated control, which was lowered by more than 50% using 14 out of the 20 potato-associated isolates.…”