Fungal seedborne pathogens infecting potato seed tubers from Turkey, 2011–2014

Abstract

Samples of potato tubers from commercial seed stocks and from grower’s own seed in Turkey were received from 2011 through 2014. Six potato cultivars were involved: Agria (2011–2014); Marabel (2011–2014); Marfona (2012–2014); Hermes (2012–2014); Jelly (2013–2014); and Lady Olympia (2013–2014). Fifty tubers from each sample were examined macroscopically for fungal diseases. Eyes were excised from a 25-tuber subsample and were incubated and examined for pathogenic fungi. Twenty-five tubers were stored on trays to sprout and were examined for diseases and sprouting in May. Finally, in most years, samples of 25 tubers were wounded by dropping them onto expanded metal, after which they were stored at 5 °C and examined for dry rot after 12 weeks. Amounts of disease varied between years; during the 4 years, black scurf and powdery scab on Agria tended to increase, while black dot and late blight decreased. On average, 39% of Agria tubers were affected with black dot, 21% with black scurf and 10% with powdery scab. Dry rot affected 4% of tubers, and 91% of the isolates from rot were identified as Fusarium sambucinum Fuckel. Wounding tubers increased the incidence of dry rot threefold. During 2011–2012, late blight affected 3% of Agria tubers but fewer in later years and in other cultivars. Marabel had the most common scab (14% tubers), and Jelly had the most dry rot (7% tubers); this disease was increased by wounding the tubers. Conidiophores of Helminthosporium solani (silver scurf) were more common on excised eyes of Marfona, Lady Olympia and Jelly than those of other cultivars, and isolated verticillate conidiophores that developed on the side of incubated eye plugs of Agria and Marabel stocks yielded pure cultures of Verticillium dahliae (93%). The proportions of tubers with different diseases were affected by their regions of origin; Central Anatolia seed had the most black dot and dry rot, Western Black Sea seed had the most powdery scab, and late blight and Aegean seed had the most common scab and silver scurf. The epidemiology and management of these diseases has been studied extensively in the UK and Europe but not in Turkey. This study has highlighted the need for basic information on the epidemiology of these diseases in the soils and climates of Turkish potato growing areas and for the need to develop disease control strategies, particularly for seed potatoes.