|Norelli, John (jay) - Jay|
Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2011
Publication Date: 12/7/2011
Citation: Liu, J., Sui, Y., Wisniewski, M.E., Droby, S., Tian, S., Norelli, J.L., Hershkovitz, V. 2011. Effect of heat treatment on inhibition of Monilinia fructicola and induction of disease resistance in peach fruit. Postharvest Biology and Technology. 65:61-68. Interpretive Summary: There is increasing consumer demand to reduce their exposure to the synthetic fungicides applied to harvested commodities to prevent decay and extend shelf life. This has increased the need to find viable alternatives to disease control. Development of effective alternative strategies is a critical objective of NP-303, Plant Diseases. The use of hot water dips and brushing of harvested produce has been suggested to be a viable strategy for managing postharvest decay. Great care is needed; however, in regulating the time and temperature of exposure in order to ensure that there is no reduction in produce quality. Induction of host defenses and the biocidal effect of the high temperature on fungal spores have both been suggested to play a role in the observed effect of hot water treatments on disease management. In the present study, we examined the effect of hot water treatment on both peach fruit and the fungus that causes brown rot (the major postharvest decay organism for peach). Results indicated that fungal spores exposed to the hot water treatment experienced a significant oxidative stress brought about by the impairment of their mitochondria. This greatly impacted spore metabolism and inhibited spore germination and growth. The hot water treatment also induced a number of defense-related genes in the peach fruit which most likely contributed to the reduction in decay observed in heat-treated fruit. The greatest reduction in decay was observed when fruit were inoculated with the pathogen and then exposed to the hot water treatment. There was no adverse effect on fruit quality from the hot water treatment. This study supports the use of hot water treatments as an alternative method of disease management for harvested commodities and suggests that in terms of brown rot in peach works by both negatively impacting the metabolism of the fungus and stimulating host defense mechanisms in the fruit.
Technical Abstract: Heat treatment (wet and dry) of fruit has been demonstrated as an effective approach for managing postharvest decay. Both direct antimicrobial effects on pathogen propagules, as well as induction of host defense mechanisms, have been suggested to play a role in the observed reduction of decay. In the present study, the effect of heat treatment (HT, hot water treatment at 40 degrees C for 5 and 10 min) on Monilinia fructicola and/or peach brown rot was investigated. HT inhibited spore germination and germ tube elongation of M. fructicola in vitro. HT also triggered the accumulation of reactive oxygen species (ROS), collapse of mitochondrial membrane potential and a decrease in intracellular ATP in M. fructicola. Results of studies on peach fruit showed that HT induced the expression of defense-related genes including chitinase (CHI), B-1,3-glucanase (GNS) and phenylalanine ammonia lyase (PAL), as well as increased the activity of these enzymes in peach fruit. The HT used in this study did not appear to impair fruit quality. Our results indicate that both the direct inhibition of M. fructicola and the elicitation of defense responses in fruit by HT contribute to the observed reduction of decay in peach fruit.