What was it all about?

This investment increased the avocado industry’s knowledge on immature fruit abscission and identified management intervention points for future research. The overall aim is to maximise yield and reduce seasonal variation by equipping growers with the tools to reduce the impact of irregular bearing.

Challenge

The Australian avocado industry aims to increase production and profitability to build a sustainable and competitive supply of Australian avocados that will meet consumer requirements. Avocado is a semi-domesticated tree crop with a theoretical yield potential of 32 t/ha. Due to the irregular bearing behavior of avocado, which is primarily driven by a high rate of flower abscission due to poor fruit set and fruitlet abscission, average annual production levels across Australia are well below the theoretical yield potential.

Due to a poor understanding of the physiological basis of flower and fruitlet abscission, practical management strategies for mitigating irregular bearing have yet to be developed. Therefore, to effectively mitigate irregular bearing, an in-depth physiological understanding of flower and fruitlet abscission set is required. New knowledge on flower and fruitlet abscission can be leveraged to develop innovative methods to reduce irregular bearing to maximise yield and reduce seasonal variation.

Avocado fruitlet abscission has been studied for over 40 years, yet little progress has been made in understanding the developmental and physiological processes that drive this production problem.

Response

This research demonstrated that management of summer fruitlet abscission has the potential to increase tree productivity by ≥24 per cent. Fruitlet abscission, as well as flowering and fruit set, is impacted by the carbohydrate status of the tree and correlative dominance interactions between developing fruitlets and expanding vegetative shoots.

The results showed that fruitlet growth arrest is a primary step in the abscission process. Therefore, managing summer fruitlet abscission will require methods to mitigate the growth potential of fruitlets.

The project addressed the physiological basis of fruitlet abscission and show that fruitlet growth arrest is associated with a significant decrease in carbohydrate supply and metabolism, as well as the initiation of a sugar signaling-starvation response. Further, fruit growth arrest is associated with an alteration in hormone profiles and metabolites in the maternal tissues of the fruit.

To conceptualise the summer fruit drop, an integrative model was developed, which predicts that immature fruitlet abscission is caused by a signal(s) that act to promote a quasi-maturation pathway in the maternal tissues to arrest fruit growth and induce a conserved seed dormancy signaling pathway in the seed.

The project team proposes that the activation of this quasi-maturation pathway allows fruits to acquire the competence to abscise. Interestingly, preliminary studies suggest that the physiological basis of the initial fruitlet drop event is not conserved with the factors that drive summer fruitlet drop. Thus, it is proposed that summer fruitlet abscission involves alternations in sugar and hormone signaling that impacts carbohydrate supply and metabolism necessary for fruit growth and development.

Benefit

The new knowledge developed through this research will assist the avocado industry to reduce the impact of irregular bearing by equipping growers with knowledge and tools.

Future research aimed at determining the hierarchy of hormone signaling, will provide the basis to develop a plant growth regulator application(s) aimed at limiting summer fruitlet abscission for managing irregular bearing in avocado.