Avocado diseases affecting fruit quality

Abstract The avocado ( Persea americana Mill.) is from an ancient plant lineage, the Lauraceae. Although evidence for human consumption dates back 15,000 years, commercialisation has occurred only over the last 150 years. The most commonly traded variety was first the green-skin ‘Fuerte’ (green as it ripens), and more recently ‘Hass’, on which skin darkens when ripe. Production has been increasing worldwide, and currently about 64 countries produce avocados. The range of climates is from arid to very high rainfall and from tropical to temperate. The minimum daily temperatures are above 5°C in all avocado-growing regions because of frost sensitivity. Apart from avocado sunblotch viroid (ASBVd), most avocado fruit diseases are caused by fungi. Some fungi cause visible symptoms resulting in unmarketable fruit, and other infections in the orchard are symptomless. These symptomless infections express as rots after harvest during cold storage, transport and ripening. Most post-harvest pathogens infect through both the body of the fruit and the stem-end wound, while a few infect only through the stem-end wound. The geographic distribution of these fungi varies possibly because of differences in environmental requirements and effective quarantine measures during trade. Fungal rots can be reduced by the application of fungicides in the orchard, removing inoculum residing in dead branches and mummified fruit in the canopy, ensuring high-calcium levels in the fruit flesh are maintained, careful post-harvest handling and selling fruit as soon after harvest as possible. Some post-harvest fungicides can be effective.