Yeast extract applications to reduce the primary ascospore inoculumof Venturia inaequalis

摘要

Ascospores of Venturia inaequalis, released from pseudothecia on overwintered infected apple leaves, are the primary inoculum of the pathogen. In this study, a new sanitation strategy to reduce the ascospore inoculum was tested under orchard conditions during four overwintering periods (2011-2015). Apple scab infected leaves were collected at the beginning of leaf fall. Leaves were exposed in plastic trays (JKI Dossenheim) or on the soil (LVWO Weinsberg) and protected by a wire mesh. The leaf litter depots were treated up to four times in late autumn and winter with yeast extract preparations. In all four years the potential ascospore inoculum was reduced. Fourfold 30 % or 60% yeast extract treatments were the most effective and reduced the ascospore discharge to 99-100 %. Twofold application of a 30% yeast extract revealed a similar efficacy. Analyses of biological oxygen demand in the leaf litter depots indicated an increased microbiological activity. Additionally, the treatments enhanced the attraction of leaf litter for earthworms, which led to an accelerated ingestion rate. Leaves treated three times with a 6% yeast extract or two times with a 10 % or 20 % yeast extract were removed completely until the beginning of ascospore maturity in 2013-2015. By comparison, up to 28 % of the untreated leaves were not ingested. The results demonstrated that the performed leaf litter treatments with yeast extracts reduced the primary ascosporic inoculum almost completely, and thus might contribute to a better management of the disease. Obviously, apple scab control was achieved by enhanced microbiological and earthworm activity.