Etiology of a Tuber Rot and Foliar Blight of Potato Caused by Phytophthora nicotianae

Abstract

Taylor, R. J., Pasche, J. S., and Gudmestad, N. C. 2015. Etiology o f a tuber rot and foliar blight of potato caused by Phytophthora nicotianae. Plant Dis. 99:474-481. Although Phytophthora nicotianae is not normally considered to be an important pathogen of potato (Solanum tuberosum), intermittent out breaks o f a foliar blight and tuber rot have been reported in the United States over the past 75 years. Due to the sporadic nature of these reports, little is known about the etiology o f the disease in potato. However, foliar disease and tuber rots caused by this pathogen are usually centered near areas of standing water in the field and along pivot tracks. Moreover, soil particles adhering to the foliage o f infected potato plants suggest that wa ter splash is involved in P. nicotianae dissemination and infection. Soil infestation and water splash dissemination studies were conducted under greenhouse conditions to examine the role that zoospores of P. nicotia nae may play in disease on potato. In the soil infestation study, inoculum of P. nicotianae was added to soil at four rates (0.0, 1.0 x 1 0 ,5 .0 x 103, and 4.0 x 104 zoospores/ml) and three timings (at planting and 7 and 14 days after planting). Direct infection o f aboveground plant tissues was achieved via splash dissemination of inoculum onto potato foliage. All soil infestations significantly reduced emergence, with the exception of the 1.0 x 103 zoospores/ml treatment, and no plants emerged from soil infested with 4.0 xlO 4 zoospores/ml. Significant reductions in stem num ber were observed with infestations of 1.0 x 103 and 5.0 x 103 zoospores/ ml at planting and 5.0 x 103 zoospores/ml at 7 days after planting. Prog eny tuber infections were confirmed with infestations at 1.0 x 103 zoospores/ml at planting and 7 days after planting. Lesions developed on leaflets, petioles, leaf axils, and stems in all water splash dissemination treatments within 3 days o f inoculation, significant differences in the le sion number were observed, and disease severity generally was propor tional to inoculum concentration. Relative area under the disease progress curve o f the 5.0 x 103 and 4.0 x 104 zoospores/ml splash dis semination treatments was significantly greater than the 0.0 zoospore and 1.0 x 103 zoospores/ml treatments. Progeny tuber infections were ob served with all water splash dissemination treatments but infection rates did not differ significantly among treatments. These studies confirm the hypothesis that water splash dissemination of P. nicotianae inoculum is a likely means by which infections of this pathogen are initiated in potato. The oomycete Phytophthora nicotianae Breda de Haan (= P. parasitica D astur) is a p a thogen w ith an extensive and diverse ho st range that encom passes num erous fam ilies o f w oody and flow ering p lan ts and is capable o f infecting o v e r 300 species (14). T his pathogen com m only causes ro o t and crow n rots, the m ost notable o f w hich are b lack shank o f tobacco (70) as w ell as foot rot, gum m osis, and roo...

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“…Previous studies have indicated that P. nicotianae can cause potato tuber rot and eggplant fruit rot. Symptoms of potato infection were characterised as black spots with brown edges, and eggplants were infected with brown and sunken circle spots (Taylor et al 2015;Garcia-Estrada et al 2020). Potatoes and eggplants were selected as experimental materials for inoculation trials, having the same maturity, similar size, disease-free, and uniform weight (110 ± 10 g).…”