Biological Control and Re-curing of Sweet Potato Roots as Alternatives for Managing Rhizopus Soft Rot

View the project final report

Commodities

• Vegetables: sweet potatoes

Practices

• Pest Management: biological control, integrated pest management, physical control

Rhizopus soft rot (RSR), caused by the wound-dependent fungus Rhizopus stolonifer is among the most devastating postharvest diseases of sweetpotato (Ipomoea batatas). Roots are normally cured following harvest to heal wounds, thereby minimizing the risk of RSR infection in storage. During packing however, sweetpotato roots are treated with the fungicide dicloran (Botran®). Increasing concerns about pesticide residue on the sweetpotato roots poses the need for alternative ways of managing RSR. Even though the potential of using biological control or re-curing roots has been demonstrated by a few authors, there is a need to research further to determine the optimal application and determine if combining these methods would improve the level of control. The objective of this two-year project was, therefore, to evaluate the effectiveness of integrating improved resistance to RSR with the biological control product, P. syringae strain ESC-10 (Bio-Save 10LP), applied either as an overhead spray or as a dip to sweetpotato roots; and re-curing sweetpotato roots on the incidence of RSR in comparison to the standard dicloran. These practices were evaluated individually and in combination. Five predominant commercial cultivars Beauregard, Bayou Belle, Bellevue, Orleans, and Covington were grown according to standard practices. At 120 and 145 days in year 1 or 130 and 150 days after harvest in year 2, sweetpotato roots were artificially wounded, inoculated, subjected to the treatments, and evaluated for RSR incidence up to 14 days. Analysis of the response variable percent RSR revealed significant interactions, as well as significant differences between treatments, cultivars, and sampling times in each year. The results suggested the need for cultivar and time-specific recommendations, and the need to consider all possible variables in the development of RSR management programs.

• To evaluate the effectiveness of the biological control product, Pseudomonas syringae strain ESC-10 (Bio-Save 10LP) on the roots of five sweetpotato cultivars with varying resistance at the recommended label rate and applied either as a spray or as a dip.
• Assess the effects of re-curing roots for 24 hours after wounding, five sweetpotato cultivars with varying resistance, inflicted with one wound type (bruise) on the incidence of RSR.
• Assess the combined effects of the biological control product Bio-Save 10LP, applied to sweetpotato roots of varying RSR resistance as a dip and spray, followed by re-curing 24 hours on the incidence of RSR.