Allium fistulosum L. Alleviates Apple Replant Disease by Suppressing Fusarium solani

Fusarium solani has often been isolated from replanted apple roots, suggesting that it is associated with apple replant disease. The mechanism underlying the ability of the mixed cropping of apple trees with Allium fistulosum L. to alleviate apple replant disease remains unclear. The aim of this study was to determine the pathogenicity of the Fusarium solani isolate HBH 08 isolated from diseased roots and the effect of A. fistulosum L. and its root secretions on Fusarium solani isolate HBH 08 and apple seedings. The field experiment showed that A. fistulosum L. not only significantly reduced the amount of the Fusarium solani isolate HBH 08 in replanted soil but also increased the biomass of the grafted apple seedlings. The GC-MS analysis indicated that dimethyl disulphide and diallyl disulphide were active molecules in the root exudates of A. fistulosum L. They inhibited the growth of the Fusarium solani isolate HBH 08 mycelium and decreased the number of spores germinated. In addition, these compounds reduced the amount of the Fusarium solani isolate HBH 08 under replanted conditions and promoted the growth of grafted apple seedlings. Overall, mixed cropping with A. fistulosum L. might be an effective approach for cultivating apple trees and controlling apple replant disease.