Enhancement of disease resistance and health-promoting properties of fresh fruits and vegetables by postharvest conditioning with controlled abiotic stresses

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Our goal to date has been to develop effective post-harvest preservation methods for fresh fruits and vegetables. One approach that we have been actively pursuing is the intensification of the natural defenses of the plant tissue against diseases and delaying senescence process by hormetic doses of UV-C. One of the defense mechanisms of interest was on the elicitation of antimicrobial phytoalexins in response to hormetic doses of UV-C. In the proposed program, we entertain an integrated approach to elicit not only plant-protecting compounds and other defense reactions but also to accumulate health-beneficial compounds (nutraceuticals) in fresh produce. Since the major roles of plant secondary metabolites are to protect plants from biotic and abiotic stresses, it is conceivable that their levels can be enhanced using this principle. Accumulation of such metabolites often results in plants exposed to abiotic stresses or signal molecules. Thus the objective of this research is to enhance the disease resistance and health-promoting properties of fresh fruits and vegetables through elevating the levels of plant defense and nutraceutical secondary metabolites by post-harvest conditioning with hormetic doses of abiotic stresses and plant signal modulators in a controlled manner. Studies will be carried out initially with carrot which is a long-term storable crop but susceptible to various pathogens; and contains phytoalexins and anticancer compounds, some of which exhibit both activities. Specifically, the research involves: (1) characterization of various abiotic stresses for their oxidative stress intensity as well as profiles of redox signals and hormonal signals, that underlie abiotic stress-induced secondary metabolites, and the determination of the hormetic thresholds of the stresses in selected crops; (2) screening of hormetic doses of stresses and plant signal modulators for their potential to enhance active secondary metabolites; (3) evaluation of cross-interactions between complementary stresses and/or stresses and signal modulators in the enhancement of desirable secondary metabolites; and (4) evaluation of the dynamics of the disease resistance and titers of the active compounds elicited in response to selected stresses during storage and explore ways to maintain their enhanced attributes. Such a novel approach to the preservation of fresh crops will not only help the fresh produce industry to extend the storability of their crops and reduce post-harvest losses without resorting to chemical programs, but also help them to ensure a healthier population.