A Rapid Technique for Multiple-race Disease Screening of Phytophthora Foliar Blight on Single Capsicum annuum L. Plants

Abstract

<jats:p>Phytophthora blight, caused by the oomycete <jats:italic>Phytophthora capsici</jats:italic> Leon., is a major disease that threatens production and long-term viability of the chile pepper (<jats:italic>Capsicum annuum</jats:italic> L.) industry. For each phytophthora disease syndrome such as root rot, foliar blight, and stem blight separate and independent resistant systems have evolved in the host. In addition, several physiological races of the pathogen have been identified. A novel, effective, and accurate screening technique is described that allows for multiple races to be evaluated on a single plant of <jats:italic>C. annuum</jats:italic>. The <jats:italic>P. capsici</jats:italic> resistant line Criollo de Morelos-334, a susceptible cultivar, Camelot, and three New Mexico Recombinant Inbred Lines, -F, -I, -S, were used to evaluate the new technique for phytophthora foliar blight multiple-race screening. Using three <jats:italic>P. capsici</jats:italic> physiological races, no interaction among the physiological races was observed with this technique. This novel technique provided a rapid disease screen evaluating multiple physiological races for phytophthora foliar blight resistance in a single chile pepper plant and can assist plant breeders in selecting for disease-resistant plants.</jats:p>

Identification of Novel Physiological Races of Phytophthora capsici Causing Foliar Blight Using the New Mexico Recombinant Inbred Pepper Lines Set as a Host Differential

“…A total of 12 P. capsici isolates from two states in the United States and three other countries were used in this study (Table 1). The inoculum preparation followed the procedures of Monroy-Barbosa and Bosland (2010). The isolates were maintained in darkness separately on water agar medium [2% agar (Bacto agar; Benton, Dickinson and Co., Sparks, MD)] at 24°C in parafilmed petri plates (100 · 15 mm).…”

“…SCREENING METHOD. The plants were inoculated following the multiple-race disease screening technique described by Monroy-Barbosa and Bosland (2010). Three mature leaves were randomly selected per single plant.…”

“…The plants were rated with the following disease assessment scale: 0 = no symptoms, 1 = small lesion under the paper disc area (small, dry spots, with defined borders; lesion associated with hypersensitive response), 2 = dark green, watersoaked lesion wider than the paper disc area surrounded by pale yellow undefined borders, 3 = 15% to 49% of leaf area is wilted (scalded or necrotic), 4 = 50% or more of the leaf is wilted, and 5 = 100% of the leaf is necrotic or the leaf had abscised from the plant. As described by Monroy-Barbosa and Bosland (2010), each leaf displays an individual phenotypic reaction toward the specific isolate. Plants were considered resistant when the leaf scored 0 and 1, whereas leaves scoring 2 through 5 were considered susceptible phenotypes.…”

‘NuMex Vaquero’ Jalapeño

“…For foliar blight resistance, each isolate of P. capsici was tested on a total of 24 plants with three replications of eight plants each. To test for foliar blight resistance, seedlings were inoculated at the four-to six-true leaf stage using three mature leaves selected from each plant (Monroy-Barbosa and Bosland, 2010). A 0.5-cm diameter paper disc made from seed germination paper was placed on the surface of each leaf.…”

“…The test results indicated that 'NuMex Vaquero' possessed resistance to phytophthora root rot races 2 and 3 and phytophthora foliar blight race 2 ( Bosland and Lindsey (1991). x Foliar blight screening technique followed the procedure described in Monroy and Bosland (2010). w R = resistant; S = susceptible.…”