Inhibitory Effect and Mechanism of Composite Coating Containing Oleaster Gum and Cuminal on Postharvest Pink Mold Rot of Tomatoes

Pink mold rot is one of the major diseases of tomatoes, which can occur before and after harvest, causing great losses in tomato production, storage and transportation. This study investigated the in vitro inhibitory effect of cuminal against Trichothecium roseum Pers. Link, the fungal pathogen causing pink mold rot of tomatoes. The inhibitory effect of a composite coating consisting of cuminal and oleaster gum on disease incidence in tomatoes artificially wounded and inoculated with T. roseum and the effect of the composite coating on disease resistance in tomato fruit were evaluated. The results showed that cuminal effectively inhibited the spore germination and mycelial growth of T. roseum under in vitro conditions, cuminal at a concentration of 0.1 μL/mL inhibited colony growth by more than 80%. Under in vivo conditions, the composite coating significantly inhibited the growth of T. roseum on tomato fruit, delayed lesion expansion and reduced decay incidence. After 9 days of storage, the lesion diameter and the decay incidence of the fruit treated with the composite coating containing 30 mg/mL oleaster gum and 0.2% (V/V) cuminal were 36.7% and 69.2% of those in the control group, respectively. The composite coating effectively increased the H₂O₂ content of tomato fruit during the early stage of storage, increased enzyme activities such as peroxidase (POD), phenylalanine ammonia-lyase (PAL) and 4-coumarate-CoA ligase (4CL), and enhanced the accumulation of total phenols and flavonoids in tomato fruit. These results suggest that the composite coating containing oleaster gum and cuminal can effectively inhibit the occurrence and development of postharvest pink mold rot of tomatoes, and its mechanism is not only related to the inhibition of pathogen growth by cuminal, but also to enhanced disease resistance in tomato fruit.