Species of Phytophthora are ubiquitous in ornamental production resulting in significant crop losses. In Tennessee, national surveys for the sudden oak death pathogen Phytophthora ramorum in 2004 and 2005 led to the isolation of Phytophthora species causing disease in nursery-grown or handled woody ornamentals or both. Isolates recovered were identified to species using direct sequencing of the internal transcribed spacer and examination of morphological characters. Six known species (P. cactorum, P. citricola, P. citrophthora, P. nicotianae, P. palmivora, P. tropicalis) and one newly described species (P. foliorum) were recovered from ericaceous hosts. The most common species recovered were P. citricola and P. citrophthora. Genetic analysis using amplified fragment length polymorphism (AFLP) markers revealed intraspecific genotypic diversity as well as isolates with identical AFLP genotypes from multiple locations across multiple years. This work provides evidence for species and genotypic diversity of Phytophthora recovered in Tennessee as well as insight into the movement of individual genotypes in woody ornamental production.
Ryan S. Donahoo and Kurt H. Lamour
Naomi R. Smith, Robert N. Trigiano, Mark T. Windham, Kurt H. Lamour, Ledare S. Finley, Xinwang Wang and Timothy A. Rinehart
Flowering dogwood (Cornus florida L.) is an important tree of forests and urban landscapes in the eastern United States. Amplified fragment length polymorphism (AFLP) markers were generated from genomic DNA of 17 cultivars and lines, and four duplicate samples of selective cultivars. Specific markers were identified for all except the following two lines and cultivar: MW94-67, MW95-12, and ‘Plena’. A dichotomous cultivar identification key was constructed based on AFLP data, and specific peaks or combinations of peaks were identified for all cultivars and lines. The key was assessed with seven anonymous (unlabeled) dogwood samples, and all unknowns except one were identified using the dichotomous key. Two of the unknown samples, ‘Cherokee Chief’ and ‘Cherokee Brave’, were difficult to distinguish using the AFLP markers. Intracultivar variation, up to 36% dissimilarity, was observed between duplicate samples of the same cultivar from different trees, suggesting that some mislabeling of trees had occurred at the nursery. The cultivar-specific AFLP markers can be used in breeding applications, patent protection, and in future projects, such as mapping the C. florida genome.
Alfredo Reyes-Tena, Arturo Castro-Rocha, Gerardo Rodríguez-Alvarado, Gerardo Vázquez-Marrufo, Martha Elena Pedraza-Santos, Kurt Lamour, John Larsen and Sylvia Patricia Fernández-Pavía
Phytophthora blight of vegetables caused by Phytophthora capsici causes significant economic losses in production of Solanaceae and Cucurbitaceae crops in Mexico. The development of universal resistant chili pepper cultivars is challenging due to the diverse virulence phenotypes produced by P. capsici. The objective of the study was to characterize the diversity of phenotypic interactions for P. capsici isolates recovered from production fields in Michoacán, Mexico, to facilitate the development of resistant cultivars. Virulence phenotypes were characterized for 12 isolates of P. capsici using 26 Capsicum annuum New Mexico Recombinant Inbred Lines (NMRILs) in greenhouse conditions. Criollo de Morelos CM-334 and California Wonder were used as resistant and susceptible controls, respectively. Seedlings at the four to eight true leaf stage were inoculated with 10,000 zoospores per seedling and disease severity was evaluated at 20 days post-inoculation. Two of the P. capsici isolates did not infect any pepper host even though the isolate was less than a year old. The 10 virulent isolates were designated in 10 virulence phenotypes. The information generated by this study is of utmost importance for efforts of producing resistant cultivars specific for Michoacán producers.