Abstract
Pink rot (Phytophthora erythroseptica) of potato is a major concern in many potato production regions. The pathogen produces zoospores that serve as a primary inoculum for infection. To understand how the pink rot incidence is related to pathogen population, qualitative, and quantitative chemical analyses were conducted. It was demonstrated that P. erythroseptica zoospores required a minimal population of 103 zoospores/ml (threshold) for initiating germination and the subsequent infection; the percentage of zoosporic germination was positively correlated with the density of zoospores above the threshold. To elucidate the density-dependent behavior, zoospore exudate (ZE) was extracted from high-density (105/ml) zoospore suspension. Zoosporic inocula of P. erythroseptica at different concentrations were inoculated on potato tubers. Necrotic lesions were caused by inoculum with 100 zoospores per inoculation site; 5 zoospores per site did not cause lesions on the tuber. However, five zoospores did cause lesions when they were placed in ZE, suggesting ZE contained chemical compounds that regulate germination of zoospores. ZE was collected and analyzed using liquid chromatography mass spectroscopy (LC-MS). Results showed that the amino acid leucine was associated with zoosporic germination. Therefore, zoosporic germination and infection of P. erythroseptica were mediated by signaling molecules secreted from zoospores.
Highlights
Phytophthora erythroseptica Pethyb., the causal agent of pink rot of potato (Solanum tuberosum), is a major threat to the potato industry throughout North America, including the state of Maine (Lambert and Salas, 1994; Taylor et al, 2002; Fitzpatrick-Peabody, 2011)
Zoosporic infection results were correlated with germination, which illustrated that germination is more critical during zoosporic host infection compared with auto-aggregation for P. erythroseptica
We demonstrated that zoosporic germination and host infection of P. erythroseptica were density-dependent behaviors
Summary
Phytophthora erythroseptica Pethyb., the causal agent of pink rot of potato (Solanum tuberosum), is a major threat to the potato industry throughout North America, including the state of Maine (Lambert and Salas, 1994; Taylor et al, 2002; Fitzpatrick-Peabody, 2011). It can cause significant yield loss of potato at both field and storage stages (Vargas and Nielsen, 1972; Peters et al, 2001; Taylor et al, 2011). Sporangia produce and release multiple zoospores under optimal conditions to initiate infection
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