Abstract/Summary

Consumer demand for high quality avocados is increasing, owing to the fruit’s versatility and high nutritional value. However, avocados suffer from a variety of fungal diseases responsible for decay and loss of yield. A necrotising condition known as Stem End Rot (SER) infects the fruit before ripening and spreads from the stem attachment point down into the mesocarp tissues following exogenous ethylene exposure or during endogenous developmental ripening signals. The fungal pathogens can be partially mitigated with modern fungicides, but the high proportion of fruit that are still failing to meet postharvest quality standards indicates that preharvest fungicide application is an insufficient strategy to prevent crop loss and waste. Much of the current research is focused on fungal communities in the field, and little is known about pathogen species after the fruit enter the supply chain downstream of the orchard. To investigate the impact of SER associated pathogens at the end of the supply chain, fungal pathogens were cultured from the stem-end of avocados collected from the Greencell distribution centre in Spalding, UK. Fruit physiological characteristics, disease symptoms, and orchard location data were paired with fungal pathogens cultured from each avocado. Factors such as rainfall, temperature, and wind are known to affect which pathogen species thrive in the orchard environment. Koch analysis principles coupled with ITS sequencing were used to establish causation of SER by specific fungal species. A key question was whether the fungal species present from fruit obtained from a specific orchard varied between location and climate type. Climactic data was paired with historical records of disease incidence for selected orchards managed by the Greencell distribution centre. By correlating the identity of the isolated SER causal species with the known abiotic factors and orchard data, this research contributes to a better understanding of pathogen ecology. Whole genome sequencing of identical morphotypes obtained from different countries of origin provided an insight into the genetic variation present within SER-causing species and illustrated that the country of origin for avocados can harbour multiple strains of the same fungal species. These data lay the foundation for further study of SER causal species ecology and the development of targeted mitigation strategies.