Identification and Characterization of Pythium Species Associated with Greenhouse Floral Crops in Pennsylvania

Abstract

During 1996 to 2001, samples submitted to clinics from commercial greenhouses involved 11 species and two unidentified isolates of Pythium from 110 plant samples, five potting soil tests, and five tests of irrigation water. Pythium irregulare was found in 45% of the plant samples, four of the five water samples, and three of the five potting soils. Pythium aphanidermatum accounted for 29% of all plant but 77% of the poinsettia samples. The Pelargonium samples received were infected with P. aphanidermatum, P. dissotocum, P. heterothallicum, group F, P. irregulare, P. myriotylum, and P. ultimum. The base pair sequence of the ITS1, 5.8S, and ITS2 regions of ribosomal DNA effectively differentiated the species encountered. The ras-related protein gene sequence did not differentiate P. aphanidermatum, P. arrhenomanes, and P. deliense from one another. One isolate each of P. cylindrosporum, P. dissotocum, P. heterothallicum, P. splendens, and P. ultimum exhibited resistance to the phenylamide fungicide mefenoxam, an isomer of metalaxyl, while 38% of the P. aphanidermatum and 37% of the P. irregulare isolates were resistant.

Root and stem rot of chrysanthemum caused by five Pythium species in Japan

“…in chrysanthemum have never been reported in Japan, but P. aphanidermatum and P. ultimum have been found in the Netherlands (De Kreji and Paternotte 1999), P. splendens in Canada (Bolton 1981) and P. irregulare, P. spinosum and P. ultimum in the USA (Moorman et al 2002;Tammen and Muse 1961). In addition to the previously reported P. ultimum var.…”

Bait method to detect Pythium species that grow at high temperatures in hydroponic solutions

“…Recently, P. helicoides was reported to cause root and crown rots of strawberry and damping-off of chrysanthemum (Suzuki et al 2005;Watanabe et al 2005;Tsukiboshi et al 2007). Furthermore, P. aphanidermatum and P. myriotylum are also important pathogens in hydroponic culture systems, causing root rot of cucumber, tomato, tobacco, bell pepper, floral crops, lettuce, artichoke and other many crops (Moulin et al 1994;Jenkins and Averre 1983;Anderson et al 1997;Chellemi et al 2000;Moorman et al 2002;Stanghellini et al 1998Stanghellini et al , 2000a. All these pathogens can grow at high temperatures and may become prevalent in greenhouse conditions.…”

Molecular characterisation, pathogenesis and fungicide sensitivity ofPythiumspp. from table beet (Beta vulgarisvar.vulgaris) grown in the Lockyer Valley, Queensland

“…The genus Pythium is a member of the stramenopiles and, like the closely related oöymcota genus Phytophthora (Cooke et al 2000), is noteworthy as the causal agent of numerous economically significant diseases of horticultural and broad acre crops (Davis and Bockus 2001;Davison and McKay 2003;Martin 1995;Moorman et al 2002;Paulitz and Adams 2003;Weiland and Sundsbak 2000). Many oömycetes including the phytopathogenic Pythium spp.…”

“…In contrast, DNA-based methods are often rapid and unambiguous, and in many cases do not rely on the culture and propagation of the suspected pathogen. In most of these studies, detection and identification has been based on polymerase chain reaction (PCR) amplification of the internal transcribed spacer (ITS) region of the genomic sequence encoding rRNA genes (rDNA), including one or more of ITS I, ITS II and 5.8S rDNA (Lévesque et al 1998;Matsumoto et al 1999;Moorman et al 2002;Wang and White 1997;Weiland and Sundsbak 2000). Subsequent characterisation of Pythium isolates has been based on RFLP and/or DNA sequence analyses of the PCR amplified region or by hybridisation of the target DNA to arrays of the corresponding region from a range of oömycetes.…”

“…To a lesser extent, detection and molecular characterisation of Pythium spp. have involved analyses using targets other than rDNA, including the genes encoding for actin and the ras-related protein and mitochondrial DNA (Weiland and Sundsbak 2000;Moorman et al 2002;Wang et al 2002).…”