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How to grow the perfect Avocado

Avocado became one of the trendiest fruits on the planet, and the growing ask brings higher quality demands. Here are a few tips and tricks that will help you get the most from your crops

Avocado’s definition as a trendy “super food” is a reality: it contains important vitamins, essential nutrients, and healthy phytochemicals. Combine that with its flavor and the rich variety of culinary options, and the result is constantly increasing demand. It is expected that by 2030 Avocado will be the best-selling tropical fruit, with a projected production of 12 million tones worldwide.

The growing ask bring constant demand for higher fruit quality, specifically in attributes like skin color, taste and size. The skin color depends mainly on variety; the taste depends on its oil content and harvest date, and the size (that changes from variety to variety) is affected considerably by growing conditions.

Some avocado varieties (such as “reed”) are naturally large fruits, but others (like the most sought after “Hass” variety) are smaller. the desirable size, that yields the best prices, is sometimes hard to reach. Thus, growers may struggle to reach the market demands for size and get the best prices possible.

Avocado fruit growth is different from many other fruits. in most fruits the growth is divided to an initial stage of rapid cell division with little cell growth, and a second stage with little to no cell division during which the fruits start to accumulate sugars. In avocados, cell division continues all the way to maturation, and most cells reach their final size at an early stage and start to accumulate oil at later stages. This unique development has important effects on plant metabolism, photosynthesis, sugar accumulation and water requirements of the whole tree. Understanding these factors, their connection to irrigation and climatic conditions, holds the key to understanding Avocado fruit growth.

 

 

Water loss during photosynthesis

Like in all plants, in Avocados sugars are created during the process of photosynthesis. Atmospheric carbon dioxide is converted into sugar by organelles called “chloroplasts”, that are located mainly in the outer leaf plant cells. In the process of absorbing carbon dioxide from the air, the plant loses water vapor, in what is called “gas exchange”. the force that pulls water out from the plant to the air is also responsible for pulling water and nutrients up the plant from the soil.

Many of the processes that take place during the Avocado fruit growth are high energy-demanding, and therefore influence the water demand of the tree. Cell division demands available water that will flow into the cell and make it big enough so it can divide into two. What pulls water into the cell is the high soluble concentration maintained inside the it: that takes a lot of sugar and energy to create. That is the reason why the initial fast growth stage that follows fruit set is so sensitive to water stress, which limits both water uptake and sugar creation. That is also why water stress at this stage effects the final fruit size so much.

Another factor increasing the energy and water demand of the Avocado tree is the high oil content in the fruits. Oil is a high energy molecule created by the breakdown of sugar molecules into small parts and re-attaching them in a long chain, that is the base of the oil molecule. This process not only requires sugars as building blocks but also requires a lot of energy for the process. that again comes from sugars and photosynthesis, which means more water loss to the air. That is why the later stage of the fruit where cell division and oil accumulation take place together is also stress sensitive and any lack of water results in an almost immediate effect on fruit size.

 

Avocado trees, spoiled

Avocado trees have developed in humid rainy areas, with high supply of rainwater and well drained soils. That is why the avocado root developed to be wide and shallow, and with no fine root hairs that allow good usage of soil water. Today we are growing the “spoiled” avocado tree in very different areas, where water supply is lower, and climatic conditions are harder. This means that the avocado trees we grow may find it harder to take all the water they need from the soil in the same rate they are losing them, unlike other fruit trees under the same conditions.

In addition, we need to remember that from the tree’s point of view, the fruits don’t need to be that big: there just needs to be a bit of flesh to lure animals to feed and spread the seed. we are asking our trees to grow fruits to sizes they never intended to and in drier conditions they weren’t accustomed to where they developed.

The combination of a tree that is not accustomed to growing in dry conditions with limited water supply (and high-water demand due to constant cell division and oil accumulation) creates a challenge. To achieve high fruit size demands a fine balance of soil moisture along the growing season.

Climatic conditions also have a major influence on fruit growth, especially during heat waves. All fruit trees may struggle during heat waves, but Avocado, with its “less effective” water uptake system, struggles even more. If an avocado tree is met with a condition in which it is losing too much water to the air and can’t compensate for it from soil water, the reaction may be extreme and lead to fruit growth rate reduction, or even fruit drop.

One of the reactions of plants to high water stress is a limitation of growth rate. This mechanism causes the plant to reduce its growth potential after being exposed to high water stress. this is a protective mechanism that allows plants to adjust to changes in their environment and reduce exposure if the conditions are not suitable.

In Avocado fruit we have another factor that reacts to water stress and effects fruit growth, and that is the vitality of the seed coat. The seed coat may look like a thin insignificant layer, but in fact it’s responsible for producing a variety of growth hormones that stimulate fruit growth. In cases of extreme stress, the seed coat may undergo senescence or even abortion and stop functioning, in which case the fruit growth rate will decrease significantly.

 

What can we do? Irrigate correctly

Therefore, as farmers we need to make sure we supply the tree with optimal irrigation all season long, taking extra care during extreme weather events. Irrigation that allows easy water retention from the soil, without waterlogging it, allows the trees ideal conditions for photosynthesis and sugar accumulation, and maintains constant tree and fruit growth all along the season, so we can fulfil our crop full potential.

Trunk and fruit growth, and plant reaction to heat stress, cannot be measured by the naked eye, certainly not in real time. That brings up the need for sensing systems that will inform us on the trees growth, the fruits growth, and the reaction to weather changes.

The most suitable sensor for this goal is the Dendrometer. It uses a small piston that touches the trunk and moves in and out when the tree trunk moves. It measures the contraction of the trunk during the day when it loses more water to the atmosphere than it can regain from the soil. It also measures its expansion during the night when the tree can rehydrate, fills with water, and new cells can grow and expand in the tree and in the fruit. This cycle of contraction and expansion of the trunk is a natural process that is happening every day. Measuring it in real time allows us to adjust our irrigation so the tree does not experience high stress during the day, and maintains growth during the night. Following and keeping a steady growth trend in the dendrometer also assures stable photosynthesis and sugar accumulation, since any stress that effects these also effects the trunk behavior.

Another sensor that is very important is the fruit diameter sensor, that sits on a single fruit and measures its actual diameter live. this allows us to ensure that the fruit growth rate is uninterrupted, and to learn under what conditions its reducing and react in advance to prevent it.

In SupPlant we are using these sensors and others, like soil moisture sensors, and combine them with current and forecasted meteorological data and that enables us and our farmers a full look at the growing system. In recent years we have been working with Avocado growers around the globe, met with a variety of soils and growing conditions, from humid tropical to dry semi desert conditions, and learned to recognize the conditions in which Avocado trees experience stress, that leads to fruit growth reduction. Join our service, and we will help you grow the perfect Avocado.

 

Nitzan Shatzkin, Chief Commercial Agronomist, SupPlant

 

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