02187nas a2200145 4500008004100000022001300041245007600054210006900130260000900199300000900208490000700217520168800224100001701912856011201929 1987 eng d a0031949X00aEnhancing detection of Phytophthora cactorum in naturally infested soil0 aEnhancing detection of Phytophthora cactorum in naturally infest c1987 a14750 v773 a

Reliable methods were needed to detect P. cactorum, one of the primary causal agents of P. crown rot of apple trees, in its natural soil environment. Apple or pear fruits, used in a baiting bioassay, were ineffective at detecting P. cactorum in naturally infested soil. Apple seedlings, cotyledons and seedling leaf pieces were successful baits, but cotyledons were the most sensitive and efficient. Completely air drying soil subsamples and then remoistening them for several days before flooding and adding plant tissue baits (extended baiting procedure) greatly enhanced detection when compared with the standard direct baiting procedure without prior manipulation of soil moisture. Bioassay incubation temp., volume of water added to remoisten air-dried soil subsamples, and incubation period following remoistening all affected detection, but the photoperiod during incubation did not. The advantages of an extended baiting bioassay with apple cotyledons were: greater sensitivity than with pear or apple fruits or by direct baiting, readily available and inexpensive baits, formation of sporangia of P. cactorum directly on necrotic cotyledons, and lack of interference by contaminating Pythium species. Cotyledons were also colonized by zoospores of P. cambivora, P. citricola and P. cryptogea, but not by those of P. megasperma, P. syringae, P. drechsleri, or an unidentified Phytophthora sp. The extended bioassay procedure routinely has provided a relatively rapid and efficient means of detecting P. cactorum in a diversity of soils within and around New York apple orchards.

1 aJeffers, S N uhttps://forestphytophthora.org/references/enhancing-detection-phytophthora-cactorum-naturally-infested-soil