White rot, caused by Sclerotium cepivorum, is a devastating disease of onion, garlic, and other Allium crops. The pathogen reproduces and survives by forming sclerotia, which can survive in field soils for decades. The pathogen is host-specific to Allium spp., and sclerotia germinate in response to sulfur compounds produced by Allium roots. Sulfur-containing compounds such as diallyl disulfide (DADS) and garlic oil can stimulate sclerotia germination without host plants and effectively reduce pathogen populations before planting an Allium crop. However, garlic oil and DADS are highly volatile and challenging to handle and apply in the field. In addition, laboratory soil incubation experiments have demonstrated the strong interaction of DADS and garlic oil with soils and reduced efficiency. Therefore, this study was conducted to encapsulate DADS and garlic oil with β-cyclodextrin (β-CD) to protect sulfur volatiles from interactions with soil and against oxidation, degradation, and evaporation. Microcapsule extract analysis showed that garlic oil and DADS were successfully encapsulated with greater than 90% powder recovery. In addition, the micro-encapsulation process did not change the chemical structure, but the chemical composition was altered. Furthermore, lab and growth chamber incubation experiments revealed that DADS and DAS could be slowly released into the soil from microcapsules and worked effectively for white rot sclerotia germination. Compared to the mock-treated control, liquid DADS treatment, the microcapsules of DADS and microcapsules of garlic oil reduced sclerotia populations by between 73.7 and 82.3%, depending on the treatment. Compared to liquid DADS and liquid garlic oil, the encapsulated DADS and garlic oil are equally effective but easier to handle, providing more flexibility regarding timing, placement, and machine applications.

Jeremiah Dung

Appearances