Influence of Plant Interactions on Vesicular‐arbuscular Mycorrhizal Infections.

SUMMARY The effects of crop rotation on mycorrhizal development were examined in pot experiments, using sterilized soil inoculated with Glomus fasciculatus‘E3’ or Gigaspora margarita or unsterile soil containing mainly a type of Glomus macrocarpus var. geosporus. In four crop pairs tested, the amount of VA mycorrhizal infection in a host plant was not depressed in soil previously cropped with a ‘non‐host’ plant, even where roots of the preceding ‘non‐host’ plant were retained intact in the soil. Indeed the early establishment of VA infection in barley, lettuce and maize inoculated in sterilized soil was stimulated by the ‘non‐hosts’ oilseed rape, cabbage and sugar beet, respectively. VA hyphae were sometimes observed growing in moribund ‘non‐host’ roots. Effects of crop rotation in unsterile soil were similar but less marked. G. margarita in sterilized soil infected lettuce considerably less than other crops.