A Tale of Two Avocado Trees

Figure 1: Avoseed® is a buoyant tool that lets your avocado be  exposed to water and allows for easy visual of the germination and  growth of the seedling
Figure 1: Avoseed® is a buoyant tool that lets your avocado be
exposed to water and allows for easy visual of the germination and
growth of the seedling

Last year I decided I wanted to grow an avocado tree in the UConn Floriculture greenhouse. My friend, Aisha, gave me a seed from her home in southern California, where her family has about a dozen avocado trees in their backyard. I started Aisha’s avocado seed in water (Figures 1 and 2). People often do this because it is interesting to see how the seed germinates and puts out a stem and a leaf. I decided to grow a second avocado seed from an avocado that I got at the supermarket. I planted the supermarket seed in soil. So, it was a bit of an “experiment” to see which one grew better based on each different type of growing medium.

They’ve both been growing for almost a year now, and since then have successfully germinated, emerged, and grown into sizable plants. I have also since put Aisha’s avocado seedling in soil. Check out the photos of the avocado trees (Figure 3), and take a guess at which one you think is the healthier one. You may be surprised to find out that the shorter one is actually healthier. The health of the plants can be tracked back to the original growing conditions.

Figure 2
Figure 2

If you were to take a closer look at the leaves and the structures themselves, you’d see that the shorter one has much darker, more turgid leaves (Figures 4 and 5). The lighter green leaf color of the taller plant is a potential sign of nutrient deficiency. The turgidity of the leaves is also important. The taller tree’s curl up around the edges, and exhibit moderate wilting. This contrasts with the leaves of the shorter tree, which have the ability to remain firm. This is a result of the tissues of the shorter tree being filled with water.

Figure 3
Figure 3

These differences derive from their original growing conditions. The shorter tree started in a soil medium, and the taller tree began in a water medium. The oxygen concentrations in these two types of media are very different. The water would have had a much lower oxygen concentration than the soil, which has many pores filled with air. Plants, like us, need oxygen. In their case, it’s important for their root and root hair development. In the absence of oxygen, plants can experience poor development of these underground structures. As a result, plants with these characteristics will have a hard time taking up water and all of the nutrients dissolved in that water.

Figure 4: Leaf of taller tree (left), leaf of shorter tree (right)
Figure 4: Leaf of taller tree (left), leaf of shorter tree (right)

If you don’t care about any of this science stuff, I totally understand. You’re probably wondering ‘when can I make guac?’ Well, funny story. Neither of the avocado trees may ever produce fruit, and if they eventually do the fruits will probably be very oddly shaped. They probably will not be like the ones you see in the supermarket or even the ones you might find at Aisha’s house. This is a trait particular to avocado trees and some other tree species as well. Avocado trees cannot self-pollinate to produce fruit, so they must out-cross given the pollen of a complimentary avocado tree type. So, although, the avocadoes from which I obtained the seeds, in the first place, were normal-looking, the trees that they are developing into are unlikely to produce your typical looking avocadoes.

Figure 5: Leaf of taller tree (left), leaf of shorter tree (right)
Figure 5: Leaf of taller tree (left), leaf of shorter tree (right)

There is a way to evade this biological characteristic of avocado trees that farmers use all the time. It would be through of an ancient practice called grafting. You can think of grafting as a way of gluing the canopy part of one type of avocado tree, which produces desirable fruit, to the branch of another avocado tree variety that does not produce desirable fruit. The outcome, then, is a tree that produces desirable fruit.

That would be way too much work though. Unfortunately, I’m too broke and busy to do that. So, I’m hoping, however, that (without any sort of modification) if the trees do fruit, I hit the genetic lottery. Ideally for me that would mean a tree that produces seedless avocados. But the chances of that happening are probably around 1 in billions. Wish me luck!