Induced resistance to control postharvest decay of fruit and vegetables

More than one third of harvested fruit and vegetables are lost and do not reach the customers mainly due to postharvest decay. During the last decade, several postharvest fungicides have been excluded from the market, or their allowed residues have been significantly decreased. Therefore, there is growing interest in eco-friendly and safe alternatives to synthetic fungicides. Induced resistance has gained increasing attention as a sustainable strategy to manage postharvest decay of fruit and vegetables. Their natural resistance can be increased by various means, such as biocontrol agents or their secreted elicitors. Alternatively, physical means, such as UV-C, ozone, and heat treatment, can prime plant resistance through abiotic stress. Moreover, various defense-related phytohormones, biological elicitors, non-organic elicitors, and volatile organic compounds have been shown to induce plant resistance. During the last decades, new technologies have enabled the evaluation of gene expression, such as quantitative real time PCR and the most recent next-generation sequencing, and thus the quantification of physiological changes, which have revealed new knowledge about preharvest and postharvest induced resistance in response to various treatments. These techniques allow optimization of postharvest application of the control means, although these data cannot disregard the evaluation of in vivo effectiveness. The elicitation of host defenses prevents the appearance of resistant isolates of pathogens. Induced resistance can lead to increased levels of phenolic compounds in the plant tissues, which often have antioxidant properties that are highly beneficial to humans. Moreover, induced resistance preserves the natural microflora, which is rich in potential biocontrol agents, and which provides a combined approach in the control of postharvest decay that is sustainable and safe for both growers and consumers. This approach meets the requirements of integrated disease management on sustainable use of pesticides that in the EU is implemented through Directive 128/2009. This review summarizes recent achievements and knowledge of the elicitation of host defenses to control postharvest decay of fruit and vegetables, and provides an outlook on the new challenges in this fascinating subject.