Improving avocado fruit quality: evaluation of post-harvest treatments

There are several diseases and other physiological disorders of avocado fruit impacting the quality of product and eating experience for the consumer. Trees and fruit are pushed to their limits in terms of yields, productivity, biotic stress (diseases and insect pressure) and abiotic stress (floods, drought, low soil fertility etc). On top of this, as production volumes increase and export markets expand, fruit are stored and transported for lengthy periods after harvest and frequently subjected to undesirable spikes in temperature. No wonder fruit doesn’t always arrive in the best condition! It is the responsibility of all stakeholders in the chain to supply avocado fruit of high quality with minimal post-harvest wastage.

In Australia, the primary diseases (rots) affecting avocado after harvest are anthracnose and stem-end rot. Anthracnose is primarily caused by fungal Colletotrichum species, and while fruit may be infected at any time during development, the fungus remains dormant for many months after penetrating the fruit cuticle without causing obvious symptoms.

After harvest, during the ripening process, the fungus resumes growth causing disease symptoms. Several fungal species are associated with stem-end rot, including Colletotrichum spp, Diaporthe (Phomopsis) spp, Pestalotiopsis and species in the Botryosphaeriaceae family (Lasiodiplodia spp., Fusicoccum spp, and Neofusicoccum spp).

These fungi are frequently present as endophytes internally infecting living plant tissues without causing any visible disease for at least part of their life cycle. They may colonise the fruit peduncle and be present in the stem end of harvested fruit. During ripening the fungi recommence growth and become pathogens, causing disease emanating from the stem end, frequently tracking along the vascular strands within the pulp. Stem-end rot is frequently worse in fruit from stressed trees, such as those in decline from Phytophthora root rot.

Growers should not rely solely on post-harvest fungicide treatments to manage fruit diseases such as anthracnose and stem-end rot. Management of these diseases must commence on-farm with a combination of tools for high-health orchards. These include orchard hygiene and canopy management to reduce fungal spore load and infection events, strategic applications of registered fungicides, optimal irrigation and nutrition for healthy trees and robust fruit, and careful harvest and post-harvest practices (find out more in the Best Practice Resource).

Research undertaken in AV16007 evaluated post-harvest treatments including Graduate A+, a fungicide comprised of two active ingredients, azoxystrobin and fludioxonil, as well as electrolysed oxidising (EO) water, a chlorine-based sanitiser, for their effect on anthracnose and stem-end rot compared with the industry standard prochloraz.

Key messages from the research were

- Premium fruit quality is the responsibility of everyone along the supply chain, and begins with good orchard management to limit infections from fungi causing anthracnose and stem-end rot during fruit development.

- Post-harvest treatments should not be used as a “Band-Aid” to cure infected fruit coming into the supply chain.

- Graduate A+ is an effective post-harvest treatment, particularly for stem-end rot

- Further trials are required to test electrolysed oxidising (EO) water under commercial conditions, but initial work is promising.

- Combinations of EO water and Graduate A+, or other products as they are available, may enhance robustness of fruit through extended storage and transport chains, resulting in premium quality fruit at point-of-sale and a pleasurable experience for the consumer.

Click the link below for full results and discussion of the research.

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