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Biocontrol agents are an environmentally friendly alternative to chemical pesticides against phytopathogens. The effectiveness of metabolites produced by Bacillus atrophaeus B5 for controlling anthracnose produced by Colletotrichum gloeosporioides in harvested fruit and the possible action mechanisms have been studied. Avocado fruit treated with metabolites reduced 54% of anthracnose incidence and nearly 70% of the lesion than untreated fruit. The treatment enhanced the activities of peroxidase, polyphenol oxidase, and phenylalanine ammonia-lyase. Additionally, the transcription of PAL and EIN3-like genes related to defense were increased. These results suggest that metabolites produced by B. atrophaeus B5 enhance disease resistance against C. gloeosporioides in avocado fruit. In the fruit, the induced resistance is related to the priming of defense responses. Metabolites in the cell-free supernatant could also be a potential biological preservative for avocado protection.

Fruit losses and wastage are mainly due to postharvest diseases; their control is reduced with pesticides. The excessive use of synthetic fungicides has caused harmful effects on human health and the environment, so it is therefore necessary to reduce their use. The development of new innocuous strategies has led to the use of compounds of natural or biological origin with the capacity to induce the plant defense system, which improves the fruit’s response against future pathogen attacks in addition to reducing the incidence of postharvest diseases. These compounds are known as “elicitors”. Although the use of molecular tools such as RT-qPCR or the measurement of the enzymatic activity of molecular markers makes it possible to determine the activation of the plant defense system in response to the application of an elicitor compound, in recent years, omics technologies such as the transcriptome, proteome, or metabolome have provided new and interesting information that helps to elucidate the molecular aspects involved in the activation of the plant defense system in response to the application of elicitors. This review summarizes recent advances in molecular aspects, highlighting the contribution of omics technologies to a better understanding of fruit defense mechanisms induced by different elicitors.

Avocado (Persea americana) is one of the most important crops in Mexico as it is the main producer, consumer, and exporter of avocado fruit in the world. However, successful avocado commercialization is often reduced by large postharvest losses due to Colletotrichum sp., the causal agent of anthracnose. Chitosan is known to have a direct antifungal effect and acts also as an elicitor capable of stimulating a defense response in plants. However, there is little information regarding the genes that are either activated or repressed in fruits treated with chitosan. The aim of this study was to identify by RNA-seq the genes differentially regulated by the action of low molecular weight chitosan in the avocado-chitosan-Colletotrichum interaction system. The samples for RNA-seq were obtained from fruits treated with chitosan, fruits inoculated with Colletotrichum and fruits both treated with chitosan and inoculated with the fungus. Non-treated and non-inoculated fruits were also analyzed. Expression profiles showed that in short times, the fruit-chitosan system presented a greater number of differentially expressed genes, compared to the fruit-pathogen system. Gene Ontology analysis of differentially expressed genes showed a large number of metabolic processes regulated by chitosan, including those preventing the spread of Colletotrichum. It was also found that there is a high correlation between the expression of genes in silico and qPCR of several genes involved in different metabolic pathways.