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Charles S. Krasnow, Andrew A. Wyenandt, Wesley L. Kline, J. Boyd Carey and Mary K. Hausbeck

with 100% for the control ( Meyer and Hausbeck, 2013 ). Despite the effectiveness of soil-applied fungicides in phytophthora management, the labels of oomycete-specific fungicides may not support this application method ( Bird et al., 2016 ; Sanogo and

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Lindsay E. Wyatt, Amara R. Dunn, Matthew Falise, Stephen Reiners, Molly Jahn, Christine D. Smart and Michael Mazourek

Kim, 1995 ; Oelke et al., 2003 ). Phytophthora blight is caused by the oomycete pathogen Phytophthora capsici, which can infect a wide range of vegetable crops ( Crossan et al., 1954 ; Polach and Webster, 1972 ). Management of phytophthora blight

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William L. Holdsworth, Carly F. Summers, Michael Glos, Christine D. Smart and Michael Mazourek

disease is caused by the oomycete pathogen Pseudoperonospora cubensis (Berk. & Curt.) Rostov., which has a host range consisting of more than 60 species belonging to 20 genera in the Cucurbitaceae family, and includes important crops such as cucumber

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Charles S. Krasnow and Mary K. Hausbeck

of seedlings to oomycete pathogens ( Koh et al., 1987 ; Lazarovits et al., 1981 ; McClure and Robbins, 1942 ; Mellano et al., 1970 ). Vegetable crops in the Cucurbitaceae and Solanaceae families develop ARR to P. capsici fruit rot ( Ando et al

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Charles S. Krasnow and Mary K. Hausbeck

has specificity toward oomycetes ( Lyr, 1995 ; Vuik et al., 1990 ). Etridiazole disrupts the lipid structure of cell membranes ( Radzuhn and Lyr, 1984 ) and inhibits respiration by binding to the mitochondrial membrane between cytochromes b and c

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Luisa Santamaria, Emmalea G. Ernest, Nancy F. Gregory and Thomas A. Evans

The oomycete Phytophthora phaseoli is one of the most threatening pathogens of lima bean (Phaseolus lunatus) in the humid Mid-Atlantic United States. In the last 60 years, P. phaseoli has evolved to overcome genetic resistance in the host and several physiological races have been identified during the last 6 decades. Six physiological races A, B, C, D, E, and F have been identified over the years. Only race F has been detected in the field over the past decade. Identifying and characterizing sources of resistance to this pathogen and determining the nature of resistance were the main objectives. Eight commercial cultivars and 35 germplasm accessions of P. lunatus were evaluated for their reaction to races E and F. Four commercial cultivars and four accessions with resistance to race E, and two cultivars and four accessions with resistance to race F were identified. None of the germplasm evaluated were resistant to both races. Five populations of F2 plants and a recombinant inbred line (RIL) population were produced and inoculated to investigate the inheritance of resistance to races E and F. Resistance to races E and F was determined to be conferred by single, independent, dominant genes.

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Charles S. Krasnow, Rachel P. Naegele and Mary K. Hausbeck

The oomycete plant pathogen Phytophthora capsici Leonian affects the cucurbit industry annually, in some cases causing 90% to 100% crop loss ( Babadoost, 2000 ; Meyer and Hausbeck, 2012 ). Michigan is a leading producer of processing squash

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Dario J. Chavez, Eileen A. Kabelka and José X. Chaparro

economic impact P. capsici syndromes can have on cucurbit production. This oomycete pathogen affects a wide range of solanaceous and cucurbitaceous plants worldwide ( Erwin and Ribeiro, 1996 ; Tian and Babadoost, 2004 ). Infection can occur at any plant

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Amara R. Dunn, Lindsay E. Wyatt, Michael Mazourek, Stephen Reiners and Christine D. Smart

pepper varieties with tolerance to the disease phytophthora blight, whereas it is less common on more susceptible varieties ( Kline et al., 2011 ). Phytophthora blight is a soilborne disease caused by the oomycete Phytophthora capsici ( Leonian, 1922

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Chandrasekar S. Kousik, Jennifer L. Ikerd, Patrick Wechter, Howard Harrison and Amnon Levi

Phytophthora fruit rot, caused by Phytophthora capsici, is prevalent in most watermelon-producing regions of southeastern United States and is known to cause pre- and post-harvest yield losses. A non-wound inoculation technique was developed to evaluate detached mature fruit belonging to U.S. watermelon PIs for resistance to fruit rot caused by P. capsici. Mature fruit were harvested and placed on wire shelves in a walk-in humid chamber [greater than 95% relative humidity (RH), temperature 26 ± 2 °C] and inoculated with a 7-mm agar plug from an actively growing colony of P. capsici. Twenty-four PIs that exhibited resistance in a preliminary evaluation of 205 PIs belonging to the watermelon core collection in 2009 were grown in the field and greenhouse in 2010 and 2011 and evaluated in the walk-in humid chamber. Fruit rot development was rapid on fruit of susceptible controls ‘Black Diamond’, ‘Sugar Baby’, and PI 536464. Several accessions including PI 560020, PI 306782, PI 186489, and PI 595203 (all Citrullus lanatus var. lanatus) were highly resistant to fruit rot. One C. colocynthis (PI 388770) and a C. lanatus var. citroides PI (PI 189225) also showed fruit rot resistance. Fruit from PIs that were resistant also had significantly lower amounts of P. capsici DNA/gram of fruit tissue compared with the susceptible commercial cultivars Sugar Baby and Black Diamond. The sources of resistance to Phytophthora fruit rot identified in this study may prove useful in watermelon breeding programs aimed at enhancing disease resistance.