Baiting, pathogenicity, and distribution of Phytophthora megasperma var. sojae in New Zealand asparagus soils

Ten-day-old asparagus seedlings floated over flooded soil were used as a bait to isolate and identify Phytophthora megasperma var. sojae. The seedlings were injured before use by removing the seed remnants and pinching the radicle and plumule with forceps. P. megasperma var, sojae was baited from asparagus soils throughout the main production areas of New Zealand. From 22 asparagus fields, several isolates were more virulent than one from an area where there was low plant survival. There was no relationship between soil types, drainage, or plant survival and presence of Phytophthora in the fields surveyed. The possible use of this technique for estimating the soil inoculum concentration for quantitative assessment of the importance of Phytophthora is discussed.