Avocados, the new agricultural gold

Avocado plant tissue culture

Did you know avocados are genetically modified?

Avocados first came into notice in Mexico in 291 B.C. However, this buttery and delicious fruit underwent domestication in 6400 B.C. This domestication is technically genetic modification as human desires lead to genetic selection and breeding. Ancient avocados are not the glorious fruit as modern avocados. Their seeds were large with a measly portion of fleshly goodness. Today, there are three main types of avocados: Mexican, Guatemalan, and West Indian dominate the current industry. The two dominant cultivars found around the world are the ‘Fuerte’ and ‘Hass’.

Money growing on trees

The market demand for avocados is growing. Between 1990 and 2020 avocado consumption in the USA saw an increase of over 600%! This correlates to an annual increase of 20% during this period. Therefore, similar to any other gold rush, many farmers are showing keen interest in growing this buttery fruit. However, there are some serious obstacles to overcome. For instance, in Australia, the price of avocados dropped as the supply and demand have shifted during the COVID-19 lockdown of 2020. The demand for avocado decreased while the supply increased, resulting in a lower market price. Consequently, the Australian avocado market is favoring higher quality. Smaller avocado farms growing higher quality rather than quantity, potentially could increase their profit margins.

With a massive surplus stock of avocados, Australian farmers are turning their excess stock into avocado oil. In some regions of the world, wooden utensils are being created using seed pulp. While others are drying out the seeds to create powders that are rich in antioxidants. The seed also creates a pink-hued dye for cosmetic and fabric use. So, there are a lot of options available to make sure avocado waste is at a minimum while making a profit.

Challenges in the avocado industry

There exist several other major challenges in avocado production. Genetic variability is one. The offspring of an avocado tree may grow differently from its parents. This could result in different fruit quality. Additionally, there is an exceptionally long juvenile period. From seedlings, avocados take around 10 years to provide fruit. It is for this reason that propagation techniques have been used in the avocado industry. Conventional propagation techniques are laborious, time consuming, as well as expensive.

A propagation method known as the ‘Frolich and Platt double grafting’ method, is frequently used in avocado agriculture worldwide. This method is over 40 years old, contains many steps and requires a wide range of conditions and hormones. The basis of this method is to use etiolation (growing in the dark) to create long thin stems. Followed by grafting (joining) of cuttings from desired trees to rootstock via a scion (a young stem). Then a rooting hormone is added just below the scion and is placed in the dark. This induces rooting above the rootstock. The method has been useful in producing avocados we know and love. However, now it is time for innovation.

Gold comes at a price

The use of old propagation techniques negatively impacts the environment. Much like mining for gold, large-scale production is often harmful to the surroundings. Commercial avocado farms in Central and South America are causing deforestation, water shortages, and eutrophication (this is when large volumes of nutrients enter water bodies due to agricultural practices resulting in high algae growth rates, often resulting in ‘green water’). This is due to the large amount of land that is required to create clones using old propagation methods, and the heavy use of pesticides. So, avocados are good for you, but bad for the environment and this is not the reputation that this superfood should have.

Plant tissue culture avocados get the nod of approval

However, plant tissue culture (PTC) may be the solution. The world's first Hass avocados produced by trees grafted on tissue culture plants in Australia have been a roaring success. Avocado enthusiasts around the world are giving the thumbs-up to PTC avocados. PTC methods in the avocado industry can help produce 500 times more plants from a single cutting than the conventional methods currently in use by most farmers.

PTC in agriculture helps reduce the time between grafting events. Explants are produced at fast rates. Therefore, once the shoots are developed, they can be grafted onto rootstocks to grow genetically identical avocado trees. Thus, speeding up production time, maintaining quality, and reducing land use requirements. Some avocado tissues can survive for more than 17 years which is useful for genetic preservation.

So many tissues to choose from, but which is the best?

Most woody plant species show more success with nodal/auxiliary bud culture compared to shoot tip culture. This buttery fruit is no exception, it seems. Taking tissues from the sides of the avocado tree has been promising. However, a few cultivars have shown variable responses to nodal culture. Certain avocado cultivars have shown that shoot tip cultures survive longer, but have poor elongation. Juvenile nodal culture seems most promising for most cultivars. While some cultivars have had a better success rate using both juvenile and mature nodal culture. The majority favors juvenile nodal culture. For woody plants in general the use of nodal explants has been a reliable source of preserving the genetic stability of elite cultivars.

Choose the right media and look after it

The choice of basal media and its constituents has a significant effect on avocado PTC. Juvenile avocado explants do not seem to be as fussy as mature explants. Mature explants are cultivar specific in their requirements for nutrients in basal media. However, fully optimizing the selection of basal media requires further research.

A major obstacle to overcome in avocado PTC is the prevention of browning of culture media. When culture media goes brown, that's a bad sign for your tissue culture experiment. Read our article, 'Browning in tissue culture media' to understand why this is a problem in PTC. The use of antioxidants has shown to drastically reduce browning in Persia americana (a cross between a Guatemalan and West Indian type avocado). The use of ascorbic acid alone and the combination of ascorbic acid and citric acid in the media yielded the highest survival rate, shoot length, and number of leaves for the explants of this avocado cultivar.

Time to trade in the pickaxes and pans for drillers and excavators

There are some challenges to overcome in avocado PTC. However, the reward for overcoming them may well be the same as finding a new vein of gold. In a world hungry for guacamole, those who can produce high-quality avocados in copious quantities frequently, will be the most successful prospectors.

By Christos Tripodis | 22-November-2021

References

  • Avocado industry tastes fruit from tissue culture-grown plants. (2021). Retrieved 29 October 2021, from https://www.northqueenslandregister.com.au/story/7285786/tissue-culture-avos-speed-up-production/?cs=4735
  • Frolich, E.F., Platt, R.G. (1971/2). Use of the etiolation technique in rooting avocado cuttings. Calinfornia Avocado Society 55, 97—109.
  • Güler, G., Gübbük, H., Arslan, M.A. (2021). The effect of antioxidants on micropropagation of avocado by nodal segments. Horticultural Studies 38(1): 50—55. DOI: 10.16882/HortiS.900936
  • Hiti-Bandaralage, J.C.A., Hayward, A., Mitter, N. (2017). Micropropagation of Avocado (Persea americana Mill.). American Journal of Plant Sciences 8(11): 1—24. DOI: 10.4236/ajps.2017.811197
  • Márquez-MartÍn, B., Barceló-Muñoz, A., Pliego-Alfaro, F., Sánchez-Romero, C. (2012). Somatic embryogenesis and plant regeneration in avocado (Persea americana Mill.): influence of embryogenic culture type. Journal of Plant Biochemistry and Biotechnology 21(2): 180—188. DOI: 10.1007/s13562-011-0091-0
  • Miller, M. (2021). Avocado glut leaves Australian farmers crushed as prices hit guac bottom. Retrieved 5 November 2021, from https://www.washingtonpost.com/world/asia_pacific/avocado-prices-australia-brunch/2021/11/03/9b5db520-32e3-11ec-8036-7db255bff176_story.html
  • Shreeves, R. (2021). 9 Ways to use an avocado pit. Retrieved 5 November 2021, from https://www.treehugger.com/ways-to-use-an-avocado-pit-4868814
  • Williams, G.W., Hanselka, D. (2020). The economic benefits of U.S. avocado imports from Mexico. Report to the Asociación de Productores y Empacadores Exportadores de Aguacate de México (APEAM, A.C.) and the Mexican Hass Avocado Import Association (MHAIA).