Phosphine fumigation followed by forced hot-air treatment for postharvest control of Bactrocera dorsalis in dragon fruit

Bactrocera dorsalis Hendel is one of the most serious pests in dragon fruit, requiring heat treatment before international trade. Here, a novel strategy of combining phosphine fumigation followed by forced hot-air treatment was developed and its effects on B. dorsalis mortality and postharvest quality of dragon fruit were evaluated. B. dorsalis 18-h-old eggs and third instar larvae were the most tolerant stages to heat treatment. The combined treatment demonstrated a significant synergistic effect. Probit analysis revealed that the heat treatment time of combined treatment required to achieve 50% mortality (95% CL) for eggs and third instar larvae was reduced to 72.5% and 66.5% of forced hot-air treatment alone, respectively. Gene expression analysis showed that phosphine fumigation dramatically inhibited induction of HSP genes in insects following forced hot-air treatment, indicating the synergistic effect might derive from the inhibition of heat-response genes by phosphine. Fruit soluble solids content and titratable acidity were not affected by the combined treatment, although respiration was slightly inhibited. This research demonstrated the synergistic effect between phosphine and forced hot-air treatment against B. dorsalis and indicated that compared to the heat treatment alone, combined treatment required less time and a lower temperature, providing great potential as a novel strategy for fruit phytosanitary treatment, especially in heat-sensitive fruit.