Importance of postharvest treatments to reduce losses in citrus fruit

Importance of postharvest treatments to reduce losses in citrus fruit

Infopost nº168, November 2021

According to the FAO, in developed countries, more than 40% of food waste in fruit and vegetables occurs at the end of the chain, in post-harvest: warehouses, platforms, distribution, retails and consumers. This is why it is essential to draw up a global strategy in post-harvest that is effective and sustainable in order to minimise losses due to fungal attacks and other physiopathologies.

In the specific case of a citrus fruit store, within this strategy, action can be taken on three different aspects:

- Disinfection: Reduction of the population of pathogenic micro-organisms and the density of spores in the store.
- Handling: Good practices in harvesting, transport and storage.
- Treatments: Adequate choice and correct application of post-harvest treatments (fungicides, detergents, coatings, etc.).

Focusing on the latter, the choice of one fungicide treatment or another will determine in many cases the success in the commercialisation of the fruit and in the avoidance of complaints at destination. For this, we must apply a global vision to the whole process, from harvesting to the final consumer; in this way, taking into account all the possible factors that may influence the infection of the fruit, we can choose the most appropriate tool/s for its control.

Harvesting and transport
This is the main critical point from the point of view of citrus postharvest pathology. The main fungal diseases of citrus (>90%) are due to what we know as wound pathogens (Penicillium digitatum e.g.) and most wounds -and micro-wounds- occur during harvesting and transport.

It is at this time that most infections occur, and the time between infection and fungicide treatment is obviously a limiting factor where the generally established norm is to treat within 24 hours of harvesting.

Fungicide treatment (drencher, pre-sorting, etc.)
When the fruit arrives at the warehouse, it must not be left in the unloading point in the sun or exposed to draughts. It must be treated quickly in a drencher, on-line drencher or pre-sizing line.

The choice of the active material(s) to be used is another critical point. The mechanisms of action of post-harvest fungicides are diverse and their comparative effectiveness in citrus, with a specific disease, must be taken into account:

- Curative control capacity: eradication of incipient infections and deactivation of spores present in the wound (for wound pathogens).
- Preventive control capability: protection of the fruit from wound infections occurring after fungicide treatment (for wound pathogens)
- Sporulation control capacity: inhibition of sporulation on the skin of the fruit and thus transmission by contact between fruit
- Inhibition capacity on latent infections (for quiescent pathogens).

Since, as we have already mentioned, most wounds and infections occur during harvesting and transport, the curative capacity of a post-harvest fungicide for citrus must be excellent, and the first thing we must take into account for its choice in post-harvest: we must have a tool that attacks (cures) the infections produced in the fruit when it enters the warehouse.

Likewise, as we have already mentioned, another factor to take into account when choosing one active material or another is the influence between the type of fungicide chosen and the time elapsed between the infection and the treatment. In this sense, Kanetis et al. (2007) studied and compared the efficacy of different fungicides for the control of Penicillium digitatum (PD) and concluded that, when the fungicide application was made between 9 and 21 hours after inoculation (infected wound), imazalil (IMZ) and pyrimethanil (PYR) showed the best control of PD, while the efficacy of other active substances was very high in the first timings but declined with increasing inoculation time. This is of greater importance the longer the distance between field and storage (fruit coming from Andalusia and treated in Valencia e.g.). This work also shows that the IMZ+PYR mixture is the most effective in rot control.

In this sense, own studies carried out by Janssen PMP corroborate the same: in PD infections over 9 hours, PYR controls green rot better than the other fungicides tested.

Distribution and marketing
Taking into account the current trend in distribution, with citrus fruit presented in prepack, girsac or nets, where, with a single rotten piece, we must remove the whole set, all of the above is essential in order to obtain a good control of rot and not have rejections or complaints.

About Fomesa Fruitech
FOMESA FRUITECH S.L.U, is a world leader in the post-harvest treatment of fruit and vegetables. It is dedicated to the manufacture of waxes, biocides, green line, fumigants, fungicides, detergents, disinfectants, coadjuvants, phyto-regulators, etc...

In advising on diseases and pathologies caused by pathogenic agents, on the application of authorised products for post-harvest treatments of different varieties of fruit, in terms of degreening and on systems and treatments for the refrigerated conservation of fruit and vegetables, etc. And in the manufacture and installation of application and dosing equipment, degreening, controlled atmosphere, control and information management.