Abstract
Fruitlet Core Rot (FCR) is one of the major postharvest diseases of pineapple (Ananas comosus var. comosus), especially on the prone variety Queen Victoria cultivated in Reunion Island. This aggressive disease is generally due to two pathogens: Fusarium ananatum and Thalaromyces stolii, and needs to be controlled during postharvest. In Reunion Island, F. ananatum is the principal causal agent impacting fruit exportation. Fruit produced for the export market is generally treated with chemicals. This type of postharvest treatment is not in line with consumer expectations, as consumers prefer fruits treated with nonharmful and natural products. The objective of this work was to study alternative postharvest treatments using the fungitoxic properties of essential oils and their ability to elicit the resistance mechanisms of the fruit. Six EAs were tested in vitro on mycelial growth of F. ananatum. Whether by volatilization or included in the culture medium, some essential oils such as thymol, eugenol, geraniol and the carvone/menthol mixture have a strong fungistatic effect. But only thymol has a fungitoxic effect. The thymol, a natural molecule synthesized by thyme (Thymus vulgaris L. thymoliferum) is the more effective in vitro and is the strongest potential to be used in postharvest treatment. Thymol, prepared at 0.025% in a terpene solvent that acts as a penetrating agent, was tested in vivo with inoculated fruits. The treatment was effective only on necrosis development from the upper part of the fruits. Pineapple polyphenol biosynthesis appears to have been suppressed by thymol treatment. Results and opportunities for this treatment are discussed. Additional experiments must be carried out in order to decide on the advisability of this type of treatment.
Highlights
Pineapple (Ananas comosus L.) is one of the ten most cultivated fruits in the world
Fruitlet Core Rot (FCR) is one of the major postharvest diseases of pineapple (Ananas comosus var. comosus), especially on the prone variety Queen Victoria cultivated in Reunion Island
The thymol, a natural molecule synthesized by thyme (Thymus vulgaris L. thymoliferum) is the more effective in vitro and is the strongest potential to be used in postharvest treatment
Summary
Pineapple (Ananas comosus L.) is one of the ten most cultivated fruits in the world. It is grown in French outermost regions, especially on the Carib islands (Guadeloupe and Martinique) and in the Indian Ocean, on Reunion Island, where it is the most important fruit crop. Pineapple (Ananas comosus L.) is a tropical and subtropical non-climacteric fruit that is well known for its high nutritional value [1]. This fruit is susceptible to a number of fungal diseases, of which FCR caused by F. ananatum is the most severe [2]. There are physiological changes following the pathogen attack, and the phenylpropanoid pathway is solicited on pineapple [5] [6] This author showed an accumulation of free coumaroylisocitrate and caffeoylisocitrate in pineapple fruitlets following infection with F. ananatum. These hydroxycinnamic acids (HCA) play an important role in plant-pathogen interactions with their antifungal properties and have an implication in lignin biosynthesis
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