A bioassay was performed using the Agrobacterium tumefaciens reporter strain KYC55/pJZ410/pJZ384/pJZ372 [46] in plate and spectrophotometric tests to determine whether this molecule is present in ZFF. LacZ activity was detected in all four positive control plates at nM concentrations of AHL but not in ZFFnic or ZFFsoj prepared

from zoospore suspensions at > 104 spores ml-1 nor in concentrated extracts from them obtained with ethyl acetate. These results indicate that zoospores from these oomycete species do not produce AHLs which therefore cannot be responsible for any ZFF activity. Temperature sensitivity of ZFF activities To begin to characterize the signal molecules in ZFF we tested their temperature sensitivity. ZFFnic did not stimulate zoospore aggregation after a freeze-thaw or heat treatment, suggesting that the molecule promoting learn more this behavior may be a protein or lipoprotein that is sensitive to heat and freezing. On the other hand, freeze-thaw did not affect the activity

of ZFFnic in promoting plant infection by zoospores (data not shown). click here In addition, ZFFnic boiled for 5 minutes remained as active as the untreated in promoting infection (Figure 4), indicating that the molecule which stimulates plant infection is temperature insensitive and different from that involved in aggregation. Figure 4 Zoospore-free fluid (ZFF) stimulation of Phytophthora infection is unaffected by heat treatment. Each leaf of Catharanthus roseus cv. Little Bright Eye was inoculated with twelve 10-μl drops of inoculum of P. nicotianae at approximately one zoospore per drop. Zoospores were suspended in (A) sterile distilled water, (B) untreated ZFF from the same species at 5 × 105 zoospores ml-1 and (C) heat-treated ZFF. Disease symptoms were photographed

after 3-day incubation at 23°C. Conclusion This study demonstrated inter-specific activities of zoospore extracellular products in promoting zoospore aggregation and plant infection by Phytophthora. Zoosporic oomycetes contain hundreds of species and are widespread in irrigation water and plant production fields. However, specific populations detected in primary inoculum sources are not in sufficient numbers Fossariinae to produce signals that could promote plant infection. Inter-specific chemical communication (probably self-interested) as a strategy used by zoosporic pathogens for effective plant infection provides insights into the destructiveness of these pathogens and the importance of the microbial community and the environment in the infection process. AI-2 was excluded as a signal for communal behavior in zoosporic oomycetes, despite its detection in ZFF and widespread presence in the environment. AI-2 synthase RPI and purified AI-2 both were not required for regulation of zoospore aggregation and infection.