YOUR PRODUCTION
Applied fruit drop investigations in avocado BY DECLAN MCCAULEY RESEARCH OFFICER, DPIRD
I
t has been suggested avocado yields could reach 32.5 tonnes per hectare but are currently not achieving this limit (Whiley, 2013).
Factors limiting yield include pollination issues, insufficient disease control, rootstock choices, and management relating to pollination and fruit retention. Fruit retention in particular is a serious problem. Avocado trees regularly set many fertilised fruits which then begin to abscise for unknown, biologically complex reasons (Gün et al., 2008) (Sawicki et al., 2015).
In order to investigate fruit retention a method was chosen whereby different chemicals were trialled to attempt to reduce fruit drop. Funding for these trials came from Hort Innovation as part of AV17006 Avocado capacity building WA. This work was done in conjunction with CSIRO who are investigating the underlying mechanisms of fruit drop. Three chemicals were used Glycine betaine (GB), Aminoethoxyvinylglycine (AVG) and Maxcel®. GB is a compound that occurs naturally in plants and is naturally accrued to provide stress
protecting effects. Trials with GB in South Africa have been promising so it was decided to trial GB in our experiment to test its effectiveness on fruit retention (Blakey, 2015). The product used in the South African trials that contains GB is called Greenstim®. Both Greenstim® and purer lab grade GB were used in our experiments. AVG is a well-known ethylene biosynthesis inhibitor and since ethylene has been suggested as a regulator of fruit drop (Sawicki et al., 2015) it could have an application for avocados. Maxcel® is a synthetic cytokinin normally used in the apple industry to induce fruit drop. Cytokinins are plant hormones with roles in regulating cell growth and the development of various organs in the plant, such as the roots. They also control leaf and flower drop (Raines et al., 2016). In order to evaluate these chemicals two approaches were taken. One approach was to apply GB by spray to trees under induced drought stress. The drought stress was induced to try and force some fruits to drop. As defoliation is known to cause massive fruit drop, the other approach was to defoliate some trees and dip individual fruits with either AVG, GB or Maxcel®.
Fruit retention is a serious problem.
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WA Grower WINTER 2020
