D. C. Erwin

Phytophthora Database: A Forensic Database Supporting the Identification and Monitoring of Phytophthora

Phytophthora spp. represent a serious threat to agricultural and ecological systems. Many novel Phytophthora spp. have been reported in recent years, which is indicative of our limited understanding of the ecology and diversity of Phytophthora spp. in nature. Systematic cataloging of genotypic and phenotypic information on isolates of previously described species serves as a baseline for identification, classification, and risk assessment of new Phytophthora isolates. The Phytophthora Database (PD) was established to catalog such data in a web-accessible and searchable format. To support the identification of new Phytophthora isolates via comparison of their sequences at one or more loci with the corresponding sequences derived from the isolates archived in the PD, we generated and deposited sequence data from more than 1,500 isolates representing the known diversity in the genus. Data search and analysis tools in the PD include BLAST, Phyloviewer (a program for building phylogenetic trees using sequences of selected isolates), and Virtual Gel (a program for generating expected restriction patterns for given sequences). The PD also provides a customized means of storing and sharing data via the web. The PD serves as a model that easily can be adopted to develop databases for other important pathogen groups.

An Improved Synthetic Medium for Oospore Production and Germination of Several Phytophthora Species

Growth of Phytophthora arecae, P. cactorum, P. cambivora, P. capsici, P. cinnamomi, P. citricola, P. citrophthora, P. colocasiae, P. cryptogea, P. drechsleri, P. erythroseptica, P. fragariae, P. heveae, P. lateralis, P. meadii, P. megasperma, P. megasperma var. sojae, P. palmivora, P. parasitica, and P. syringae on a chemically defined medium was comparable to that on a V-8 juice agar medium. A majority of the species produced oospores on the synthetic medium. Oospores were also produced by the interspecific hybrids, P. capsici (Al) X P. parasitica (A2), P. capsici (Al) x P. palmivora (A2), P. cinnamomi (A1) X P. cambivora (A2), P. cinnamomi (A1) X P. drechsleri (A2), and P. parasitica (A1) X P. citrophthora (A2). Germination of oospores obtained from the synthetic medium was comparable to, or better than that observed for oospores produced on V-8 juice agar medium.

Morphology, plasmolysis, and tetrazolium bromide stain as criteria for determining viability of Phytophthora oospores

Viability of Phytophthora oospores was determined by morphology, ability to plasmolyze in osmotica and by rose-colored staining with tetrazolium bromide. Morphologically, normal oospores contained ...

Germination of Oospores Produced by Phytophthora Megasperma Var. Sojae

Thick-walled oospores of the homothallic Phytophthora megasperma var. sojae contained a large refractile body and two smaller pellucid bodies which prior to germination appeared to be absorbed. Whe...

PHYTOPHTHORA BLIGHT OF PIGEON PEA IN INDIA

Isolations were made from blighted pigeon-pea (Cajanus cajan) plants from different locations in India. A species of Phytophthora was consistently obtained from these locations and was proved to be the causal organism involved in the disease. Based on the sporangium shape and size, oogonium and oospore formation, temperature requirements, and pathogenicity tests, we have classified these isolates as P. drechsleri f. sp. cajani. The use of formae speciales was considered appropriate because of the specificity of these isolates to pigeon pea and Atylosia spp., wild relatives of the pigeon pea.

Oospore Morphology and Germination in the Phytophthora Palmivora Complex from Cacao

Oospore morphology and germination were studied using 17 isolates representing three morphological forms (MF) of Phytophthora palmivora from cacao. Oospore production was most abundant on carrot ag...

Isolation of plasma membrane ofPhytophthora megasperma f. sp.glycinea and some properties of the associated ATPase

Abstract Plasma membrane vesicles were isolated from Phytophthora megasperma f. sp. glycinea using conventional methods of mechanical disruption followed by differential and density gradient centrifugation. The validity of presumed biochemical markers was confirmed using electron microscopy and the phosphotungstic acid-chromic acid staining procedure, which was judged to be specific for plasma membrane when performed under suitable conditions. The plasma membrane fraction showed a peak equilibrium density of 1.14 g/ml and was identified by its vanadate-sensitive Mg 2+ -dependent ATPase with an optimum temperature of 42°C and a pH optimum of 6.0 to 6.5. The activity was weakly stimulated by K + and strongly inhibited by Ca 2+ . The enzyme showed a marked specificity for ATP as a substrate compared to other nucleoside mono-, di-, and triphosphate substrates or other general phosphatase substrates. The divalent cation requirement could be met equally well by Mg 2+ and Co 2+ and, to a lesser extent, by Mn 2+ , but not by Ni 2+ , Ba 2+ , Zn 2+ , Sr 2+ , Ca 2+ , Hg 2+ , Cu 2+ , or Fe 2+ (in decreasing order of preference). Contamination by intact mitochondria (density 1.21 g/ml) or mitochondrial fragments (density 1.16 g/ml) was minimal and could be monitored by measuring cytochrome c oxidase or oligomycin-sensitive pH 8.5 ATPase.