Occurrence and Identification of Phytophthora spp. Pathogenic to Pear Fruit in Irrigation Water in the Wenatchee River Valley of Washington State

Abstract

Seven hundred forty-nine isolates of Phytophthora spp. were obtained from irrigation canals in eastern Washington State during the 1992 to 1995 and 1999 growing seasons. Isolates were retrieved using pear baiting techniques. All isolates were pathogenic to pear and were present in irrigation water beginning early in fruit development. Over the course of the 5 year study, 10 and 5% of isolates were identified as P. cactorum and P. citricola, respectively, using morphological criteria. The remaining isolates could not be identified using morphological criteria. Colony morphology of these isolates was characterized during all years of the study. In 1999, more detailed studies utilizing polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) analysis of entire internal transcribed spacer (ITS) regions (ITS1, 5.8S, and ITS2) of ribosomal DNA for 180 isolates, and sequence analysis of ITS2 for 50 isolates, were used to investigate genetic variation and phylogenetic relationships among isolates. Isolates were divided into 12 groups based on their growth type on corn meal agar. Restriction digestion of the entire ITS region with three enzymes revealed 11 restriction digestion patterns among 180 isolates. PCR-RFLP and sequence data were obtained for 12 reference Phytophthora spp. (two species in each of Waterhouse's six morphological groups). Phylogenetic analysis of ITS2 regions revealed nine clades, each with strong bootstrap support. Molecular analyses revealed 23 isolates that were in the P. gonapodyides clade, 9 in the P. parasitica clade, 1 in the P. cactorum clade, 7 in the P. citricola/capsici clade, and 4 in the P. cambivora/pseudotsugae clade. The three isolates comprising clade 5 were significantly distinct from all other Phytophthora spp. in the databases and may represent a new Phytophthora sp. Colony morphology was not consistently correlated to PCR-RFLP pattern or ITS2 phylogeny, suggesting that the former criterion is insufficient for species identification. The results of this study indicate that at least nine phylogenetically distinct taxa of Phytophthora pathogenic to pear are present in irrigation water in North Central Washington.

MultiplePhytophthoraspecies associated with a single riparian ecosystem in South Africa

“…Likewise Phytophthora diseases in agricultural and horticultural nurseries are closely linked to the presence of Phytophthora spp. present in irrigation water (Oudemans 1999, Yamak et al 2002, Gevens et al 2007, Werres et al 2007, Ghimire et al 2009, Orlikowski et al 2009). Although the incidence of sudden oak death caused by P. ramorum appears unlinked to rivers and streams (Davidson and Shaw 2003), riparian systems play an important role in early disease detection because zoospores make their way into nearby streams when P. ramorum is present in an area (Sutton et al 2009).…”

Susceptibility of common alder (Alnus glutinosa) seeds and seedlings to Phytophthora alni and other Phytophthora species

“…Production of zoospores in the presence of water significantly contributes to the dispersal of Phytophthora via irrigation (Yamak et al, 2002;Hong et al, 2006). Transportation of nursery stock and use of natural rivers and other water courses to irrigate nurseries give ideal opportunities to Phytophthora to infect and spread in those nurseries.…”

Phytophthora hydropathica y Phytophthora drechsleri aisladas de canales de irrigación del Valle de Culiacán

“…Phytophthora species require aquatic environments in order to develop their asexual life cycle and therefore spread quickly with the formation of sporangia and zoospores; for this reason, they have been regularly isolated from irrigation water channels, water reservoirs, and rivers (Sutton et al, 2009;Ghimire et al,2009;Hulvey et al, 2010;Bienapfl and Balci et al, 2014). Examples of species reported with this dispersal mean include P. cactorum, P. parasitica, P. citricola, P. gonapodyides, and P. cambivora, isolated from irrigation waters in the state of Washington (Yamak et al, 2002). Recently, one of the species with the greatest incidence in surface waters has been P. hydropathica (Brazee et al, 2016;Ghimire et al, 2011;Hulvey et al, 2010).…”

“…Algunos ejemplos de especies reportadas con este medio de diseminación son: P. cactorum, P. parasitica, P. citricola, P. gonapodyides y P. cambivora, aisladas de aguas de irrigación en el estado de Washington (Yamak et al, 2002). Recientemente una de las especies con mayor incidencia en aguas superficiales es la especie P. hydropathica (Brazee et al, 2016;Ghimire et al, 2011;Hulvey et al, 2010).…”