Ability of the lumbricid earthworms Aporrectodea rosea and Aporrectodea trapezoides to reduce the severity of take-all under greenhouse and field conditions

The influence of the earthworms A. rosea and A. trapezoides on wheat plants, grown in soil artificially infested with the take-all fungus Gaeumannomyces graminis var. tritici (Ggt) was examined. In pot trials, using a red-brown earth soil artificially infested with Ggt, the presence of the earthworm A. trapezoides (at a density equivalent to 314 or 471 m(-2)) was associated with a significant (P < 0.05) increase in shoot weight and a reduction in the severity of take-all (as measured by a reduction in the percentage length of seminal roots containing take-all lesions). In contrast, in the absence of added Ggt, shoot weight was not significantly (P > 0.05) influenced by the presence of A. trapezoides. Two field trials were conducted, in which A. rosea and A. trapezoides were added, at an equivalent density of 100 or 300 m(-2), to cylinders driven into the soil. In a calcareous sandy loam artificially infested with Ggt, the presence of the earthworms A. rosea or A. trapezoides (at these densities) was associated with a significant (P < 0.05) reduction in the severity of take-all disease. Under the same conditions, A. rosea or A. trapezoides (at an equivalent density of 300 m(-2)) caused a significant increase in shoot weight. In contrast, in the absence of added Ggt, shoot weight was not significantly (P > 0.05) influenced by the presence of A. rosea or A. trapezoides. In a second field trial in a red-brown earth, the presence of the earthworm A. trapezoides (at an equivalent density of 300 m(-2)) was associated with a significant (P < 0.05) reduction in the severity of take-all disease. Under the same conditions, A. rosea or A. trapezoides did not cause a significant increase in shoot weight. In the absence of Ggt, shoot weight was not significantly (P > 0.05) influenced by the presence of A. rosea or A. trapezoides. These results demonstrate the potential of the earthworms A. rosea and A. trapezoides, under both greenhouse and field conditions, to reduce the severity of take-all disease on wheat.