SADAMCAP, A TECHNIQUE FOR QUANTIFYING POPULATIONS OF PHYTOPHTHORA-CACTORUM IN APPLE ORCHARD SOILS

SADAMCAP (Soil Air-Dried And Moistened Chilled And Plated), proved a sensitive and repeatable technique for assessing Phytophthora cactorum populations in apple orchard soils. Air-dried soil in petri plates was moistened and incubated under lights at 22 degrees C for 96 h and then flooded with excess water and chilled at 6 degrees C for 2 h, Plates were sloped and the water was drained, vortexed for 30 s, left at ambient temperature for 10 min, and then diluted samples were plated on PARP media and colonies counted after 20, 28, and 40 to 44 h. Detailed studies of each step in the process highlighted the importance of consistency in experimental procedures. Factors such as the time drained water samples were vortexed and how long they remained at ambient temperature prior to plating had, respectively, up to a 3.5- and 7-fold effect on the colony number. Incubation of soil under lights was essential to recover high numbers of P. cactorum colonies.