Effect of the lumbricid earthworm Aporrectodea trapezoides on wheat grain yield in the field, in the presence or absence of Rhizoctonia solani and Gaeumannomyces graminis var. tritici

In a field trial in a red-brown earth, the interaction between the earthworms Aporrectodea trapezoides and A. rosea (added at an equivalent density of 100 or 300 m−2) and wheat grain yield was examined, both in the presence or absence of inoculum of Rhizoctonia solani or the take-all fungus Gaeumannomyces graminis var. tritici (Ggt). In the absence of R. solani or Ggt inoculum, neither earthworm significantly influenced plant top weight 71 days after sowing. However at harvest, A. trapezoides at an equivalent density of 100 or 300 m−2 significantly increased grain yield (by 56% and 82%, respectively) and plant top weight (by 53% and 76%, respectively). A. rosea at these densities did not significantly influence plant top weight or grain yield. In soil artificially infested with Rhizoctonia solani, there was a significant increase from 0.06 to 1.05 in the Rhizoctonia root disease rating 71 days after sowing, but R. solani inoculum did not significantly influence plant top weight or grain yield at harvest. A. trapezoides and A. rosea did not significantly influence the Rhizoctonia root disease rating and A. trapezoides (at an equivalent density of 300 m−2) was associated with a significant increase in grain yield at harvest. In soil artificially infested with Ggt, there was a significant increase from 0.2 to 94% in the length of seminal roots containing take-all lesions 71 days after sowing and plant top weight and grain yield were significantly reduced by Ggt inoculum at harvest. When the effects of the different densities of each earthworm species across all the Ggt treatments were averaged, both A. trapezoides and A. rosea (at an equivalent density of 100 or 300 m−2) significantly reduced the Ggt root disease rating. In the presence of Ggt inoculum, A. trapezoides and A. rosea (at an equivalent density of 300 m−2) were associated with a significant increase in plant top weight at harvest, but neither earthworm significantly influenced final grain yield. These results demonstrate the potential of A. trapezoides to increase wheat grain yield in the field and that this ability may be influenced by the presence of R. solani and Ggt.