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.

Abstract. A multiplex reverse transcription polymerase chain reaction (M-RT-PCR) was developed for the simultaneous detection of three major potato viruses, Potato virus X (PVX), Potato virus S (PVS) and Potato leaf roll virus (PLRV), in potato leaves and tubers (stored and dormant). Primers were designed from the coat protein gene of all three viruses and were able to detect virus in leaf RNA dilutions of 1 : 1024 to 1 : 4096 and from tuber RNA dilutions of 1 : 256 to 1 : 1024. The sensitivity of virus detection in leaves was higher than in tubers. All three viruses were successfully detected from tissues sampled from the tuber cortex, perimedulla and pith, with all PCR bands being strongest from cortex tissues. The reliability of the M-RT-PCR to detect PVX, PVS and PLRV in tubers was determined by testing 95 samples of field, greenhouse and in vitro potato plantlets from Wuhan, China and comparing the results with enzymelinked immunosorbent assays (ELISA). M-RT-PCR detected all infections found by ELISA in leaf and stored tubers. In freshly harvested tubers, M-RT-PCR proved more sensitive than ELISA, as indicated by an additional 3.2% of infections detected with the M-RT-PCR method.