Inoculum sources and infection pathways of pathogens causing stem‐end rots of ‘Hass’ avocado(Persea Americana)

Abstract

Species of Colletotrichum, Botryosphaeria, and Phomopsis causing postharvest rots in avocado (Persea americana Miller) fruits are present in the living and dead branches and twigs of avocado trees, and in the living pedicels. They dominate the fungal population within the extra‐cambial tissues but are less common within the xylem elements. There is no evidence that invasion of these tissues is pathogenic. With the possible exception of C. gloeosporioides they appear to be discontinuously present and are more properly termed phellophytes rather than endophytes. There was a higher incidence of stem‐end rots than of body rots in untreated (control) ‘Hass’ avocados in New Zealand experiments and most of these stem‐end rots were associated with B. parva and Phomopsis spp. A high proportion of stem‐end infections appeared to be initiated during harvesting. Picking the fruit by snapping the pedicels instead of clipping, as in commercial practice, resulted in an unusually high level of stem‐end rots caused by C. acutatum. Frequently sterilising the clippers used to harvest the fruits reduced the incidence of stem‐end infections, in particular those caused by B. parva, indicating that contamination of the clippers is an important source of infection. It is suggested that this contamination is probably present as fragments of infected extra‐cambial tissue.