Why stress makes avocados small, and how to fix it

Avocado crops, particularly Hass type varieties, can suffer from having small fruit. This is associated with stress which increases the proportion of small fruit on the tree. Here we explore why stress creates this problem and explore ways to improve fruit size and quality.

To understand why some fruit fail to get to a good size, we first need to understand how avocado fruits develop.

Fruit growth occurs in two distinct stages. First new cells are created (cell division) and then they are grown (cell expansion). In most fruit crops there is little overlap in the stages, with cell expansion being completed by the time a fruit reaches 2-3 mm in size, and then switching to cell expansion where the already existing cells all increase in size as the fruit grows.

Avocado are an unusual fruit, with cell division occurring over a much longer period than for most other fruit crops. In avocado the seed coat produces auxins (the hormones responsible for cell division) continually producing layers of new cells on the inside of the fruit which then increase in size under the influence of Gibberellin hormones.

However, when avocados encounter stress the seed coat can die, which prevents the fruit from producing new cells and limits maximum fruit size. The earlier in fruit development this occurs, the smaller the maximum fruit size becomes.

Managing stress is fundamental to maintaining the potential for good fruit size. Once seed coats die it is not possible to reverse, so prevention is better than cure.

Why does stress lead to seed coat abortion?

When the trees comes under stress avocados produce stress hormones, which lead to the abortion of the seed coat in some fruits. The greater and longer the stress periods the greater the proportion of ‘small fruit syndrome’.

The reason this occurs is due to the response of the crop to stress. When avocado trees encounter stressful growing conditions (heat, cold, drought, salinity, high UV) they produce peroxides and derivatives called ROS. This process is common to a wide range of different types of stress, suboptimal growing conditions that create this include heat, cold, high UV, drought, and water-logging. When ROS production is high the plants antioxidant systems that protect them fail to cope, and crops are damaged. This can lead to seed coat death in developing avocado fruit.

Indra can reduce the impact of stress

Indra is a product that helps plants protect themselves from stress. It works by stimulating the production of the plants natural protection – antioxidants (flavonoids) and polyamines (compounds that protect cell membranes).

?Indra can be used at low rates to improve a crops resilience against stress. Used regularly through the growing season it will maintain seed coat viability during stressful growing conditions

Improving the production of the plants natural stress protection compounds can dramatically improve the ability of avocados to grow during stress conditions – leading to less uneven fruit and resulting in higher yields.

There is also a link between seed coat abortion and fruit quality

The same hormone that produces cell division (auxin) is also involved in calcium absorption. Calcium absorption into the fruit is linked to polar auxin transport, which means that fruit not producing auxins are fundamentally less able to absorb calcium.

If stress is not managed well then the whole crop can lose its potential for achieving good fruit size and also the ability to maintain adequate fruit calcium levels.

Albina is a product that helps the fruit absorb calcium when auxin levels are low. It can help improve quality in crops that have experienced a stress event and can be absorbed by fruit that are producing low levels of auxins. Albina reduces problems like pedicel ring neck, and improves texture and shelf life.

Recommendations

Apply Indra or Indra Plus every 4 weeks through the growing season to reduce the impact of stress.

To help reduce the effects of cold stress use Zeme at 1L/Ha whenever there is risk of low temperatures.

To improve fruit quality apply Albina monthly from the commencement of flowering until the last pick.