SEROLOGICAL AND CONDUCTIMETRIC ASSAYS FOR THE DETECTION OF PSEUDOMONAS-SYRINGAE PATHOVAR PISI IN PEA-SEEDS

Test protocols for detecting Pseudomonas syringae pv. pisi, the causal agent of bacterial blight, in pea seeds are generally based on diluti on-plating assays. These assays are usually very specific and reliable , but are time-consuming and laborious. Tests suited for large scale s creening of seed lots are therefore needed. Conductimetric assays, imm unofluorescence microscopy (IF) and an enzyme-linked immunosorbent ass ay (ELISA) for detecting Ps. syr. pv. pisi in pea seed extracts were c ompared with dilution-plating by two extraction methods, viz. 6 h soak ing of seeds and 2 h soaking of flour of ground pea seeds in water. In general, the detection of Ps. syr. pv. pisi with conductimetric, IF a nd dilution-plating assays in the suspension water of the ground and 2 h-soaked pea samples was less sensitive than detection in suspension water of the 6 h-soaked pea seeds. The detection threshold of these as says varied per seed lot between 0 and 4.08 log cfu ml(-1) for the 6 h soaking procedure. The detection threshold of ELISA varied for both e xtraction methods generally between 4.08 and 6.08 log cfu ml(-1). Dete ction times recorded in conductimetric assays correlated well (-0.89 < r < -0.98) with the log colony-forming units of Ps. syr. pv. pisi add ed to seed extracts at 27 as well as 17 degrees C. However, confirmati on of results by isolation on semi-selective media after conductimetry was more successful at 17 degrees C than at 27 degrees C, because of the relatively lower activity of saprophytic Pseudomonas spp. at this temperature.