Date of Award

2008

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Plant, Soil, and Environmental Sciences

Advisor

David H. Lambert

Second Committee Member

Stylianos Tavantzis

Third Committee Member

Modesto Olanya

Abstract

Phytophthora erythroseptica Pethyb., causal organism of potato (Solanum tuberosum L.) pink rot is a soil-borne ubiquitous oomycete pathogen that can cause severe losses in both the field prior to harvest and during storage. The efficacy of the most effective fungicide, mefenoxam for control of P. erythroseptica is in jeopardy due to the widespread development of resistance in the US. Cultivar resistance may provide the best option for management of P. erythroseptica in the future. Recently published reports of cultivars susceptible to P. erythroseptica are based on evaluation techniques involving detached tubers and nontuber germplasm rather than field evaluations. Screening detached tubers excludes the stem stolon infection pathway by which a majority of P. erythroseptica infections occur. In tuber inoculations and field evaluations from 2004 to 2006, 24 cultivars were evaluated for their response to P. erythroseptica infection. In 2007 field trials, 15 additional cultivars were evaluated, based upon their shared lineage with those cultivars demonstrating resistance in the three previous field years. Six standard cultivars were evaluated in all four field trial years (2004-07), three resistant and three susceptible. Cultivar response was evaluated in terms of incidence of P. erythroseptica rot. The objective of this study was to conduct the first P. erythroseptica cultivar susceptibility evaluation under field conditions. This research included the development of protocol for evaluating potato genotypes in field settings as well as baseline data for comparing results obtained utilizing different evaluation techniques. Overall, in the field trials the red skinned cultivars were classified as the most susceptible or highly susceptible in comparison to other cultivars evaluated. For the 17 cultivars evaluated in all three field year trials (2004-06) Red LaSoda (21.4%) and Russet Norkotah (19.9%) were the most susceptible. Red cultivars that were evaluated for three years included Red Gold (16.8%), Red Pontiac (12%), and Dark Red Norland (10.4%). Russet type cultivars included the susceptible cultivar, Goldrush (16.9%) and those moderately resistant Ranger Russet (9.6%) and Russet Burbank (6.9%) as well as one demonstrating resistance Gem Russet (1.1%). For white type cultivars Shepody (16.3%) was susceptible, while Kennebec (4.8%) and FL-1867 (4.4%) had reasonable resistance. The white type cultivars, though variable showed the most resistance, particularly Snowden (1.5%), Atlantic (0.8%), and Pike (0.3%). The 4 cultivars demonstrating the most resistance were all 1st to 3rd generation progeny of Lenape (B5141-6). Tuber inoculations based on an in-vitro assay using zoospore suspensions did not always correspond closely to field conditions and failed to identify some cultivars having high levels of resistance under normal growing conditions. The P. erythroseptica cultivar susceptibility of most commercial cultivars is variable with few demonstrating substantial resistance. To date there has not been any single cultivar that has been shown to be immune to P. erythroseptica. With limited cultural and chemical management options for P. erythroseptica future management of the disease largely depends upon the release of new cultivars with improved resistance.

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