Inter-seasonal irregular bearing (AV23000)

What is it all about?

This research is developing a practical method for the avocado industry to mitigate summerfruit abscission and reduce irregular bearing.

Irregular bearing is a significant and strategic challenge that limits market development for the Australian avocado industry. Currently, there are no effective tools to manage irregular bearing. The inherent irregular bearing pattern of production displayed in avocado is primarily driven by poor fruit set and/or high fruit abscission.

This project will leverage the knowledge developed in AV16005 (see more below) and move to a phase of R&D focused on developing a practical application to mitigate irregular bearing driver.

The first goal of this project is to develop an understanding of the inter-seasonal impacts of plant growth regulators that could be developed to mitigate summer fruit abscission. The research team will identify an appropriate working level of plant growth regulators that act to maintain auxin activity, as well as reduce fruit ethylene and jasmonic acid levels, in two production seasons. They will also address the appropriate time to apply a plant growth regulator treatment(s).

The second goal is to clarify the opportunity to reduce irregular bearing using plant growth regulators. This is critical as the effectiveness of a plant growth regulator application requires uptake and transport to fruits. In addition, plant growth regulators often effect other hormone pathways that can negatively impact fruit growth and development. 

Background

Research from previous avocado levy project Maximising yield and reducing seasonal variation (AV16005) showed that management of summer fruitlet abscission has the potential to increase tree productivity in two different environments.

As fruitlet growth arrest is a primary step in the abscission process, managing summer fruitlet abscission will require methods to mitigate the growth potential of fruitlets.

Experimental results from AV16005 indicated that the seed coat initiates growth arrest via a sugar signaling-starvation response associated with a decrease in carbohydrate uptake and metabolism. Further, fruit growth arrest is associated with an alteration in hormone profiles and metabolites in the maternal tissues of the fruit. In particular, the seed coat exhibits a significant decline in auxin activity followed by an increase in ethylene and jasmonic acid biosynthesis.

By integrating the carbohydrate, hormone and gene expression data, an immature fruitlet abscission model was developed. This integrative model predicts that immature fruitlet abscission is caused by a signal(s) that acts to promote a maturation pathway in the seed coat, which is transmitted to the embryo and pericarp. As fruits transition to a maturation phase of development, fruit growth ceases and a conserved seed dormancy signaling pathway is induced in the seed. Moreover, the activation of the maturation pathway allows the seed coat and fruit to undergo senescence and abscission, respectively.