Thus, zoosporic oomycetes may use completely different chemicals from bacteria for quorum sensing. this website Analysis of ZFF revealed that functional signals controlling zoospore aggregation and plant infection differ in molecular composition. The former is not temperature check details labile and acts upon a restricted number of species while the latter is heat labile and non-species-specific. Identifying these molecules will facilitate our understanding of the mechanisms underlying natural plant infection by these pathogens and may lead to innovative control strategies. Methods Zoosporic oomycetes and culture conditions Four Phytophthora species, P. nicotianae (1B11), P. sojae

(28G4), P. capsici (24F4), P. hydropathica (37E6) and one Pythium species Py. aphanidermatum (18H7) were used in this study. These species are distinct in morphology and genetics [2, 47]. Specifically, P. nicotianae, P. RG7112 capsici and Py. aphanidermatum have broad host ranges while P. sojae has a restricted host range, generally infecting only soybeans and lupines. P. hydropathica (37E6) originated from irrigation water and is a pathogen of nursery plants [48]. The isolates were maintained on clarified vegetable juice agar (CV8A) medium [49] at 23°C. Preparation of zoospore-free fluid Zoospore-free fluid (ZFF)

from a particular species is designated with an abbreviated species name. For example, ZFFnic represents ZFF from a P. nicotianae zoospore suspension. ZFF

was prepared from nutrient-depleted zoospore suspensions starting with sporangium induction as described previously [18, 21]. Specifically, prior to sporangium production, P. sojae and Py. aphanidermatum were cultured for 3-4 Fossariinae days and the other species were cultured for 1-2 wk in 10% CV8 broth. After nutrient depletion (medium removal and water rinses), the mycelial mats were further incubated for 16-18 h for P. sojae and Py. aphanidermatum, 2-3 days for P. capsici and one week for the other species under fluorescent light at 23°C to obtain a desired number of sporangia. To induce zoospore release, the mats with sporangia were flooded with chilled SDW and kept under lights until the desired zoospore density was reached. ZFF was obtained by passing a zoospore suspension through a 0.2 μm pore-size filter after vortexing for 2 min. ZFF was used fresh or stored at -20°C. Freezing destroyed the aggregation-promoting activity of ZFF, but not its infection-promoting activity. Phytopathosystems, plant growth conditions, inoculum preparation and inoculation Four phytopathosystems, P. nicotianae × annual vinca (Catharanthus roseus cv. Little Bright Eye), P. sojae × lupine (Lupinus polyphyllus), P. sojae × soybean (Glycine max cv. Williams) and P. capsici × pepper (Capsicum annum cv. California Wonder) were used. Annual vinca plants were prepared in the greenhouse where 4-wk old seedlings were grown in pine bark with fertilizer for 4-6 wk.