Flowering and fruit set in Hass avocado cultivation

Technology, research, sustainability and innovation are part of the DNA of GSF Farming. The company works with the advice of experts such as the Doctor in Plant Biology, Iñaki Hormaza, who during March visited some of the company’s farms with the workshop: flowering and fruit set in Hass avocado cultivation.

Dr. Hormaza has a doctorate in Plant Biology from the University of California and Research Professor at the Higher Council for Scientific Research (CSIC) and head of the Department of Subtropical Fruit Growing at the La Mayora Institute of Subtropical and Mediterranean Horticulture (IHSM), in Malaga. His research focuses on tropical and subtropical fruit trees.

Entering the subject of flowering, explain briefly what pollination is?To be fruit there must be pollination, that is, there must be pollen that reaches the stigma, germinates and produces a pollen tube that grows along the style and produces fertilization, there is an embryo and from there a development of fruit. There are exceptions, which are parthenocarpic fruits such as bananas or some others, but generally for there to be fruit development, there must be this pollination process. It is a complex process because the microscopic pollen must get from the anthers, which is the male part of the flower, to the stigma that is in the pistil and is the female part of the flower. Pollen can reach the stigma in different ways depending on the species; in some of them, it arrives by the wind, the wind disperses the pollen, and it reaches the stigma. In others, like the avocado, it has to be caused by insects: the pollen has to stick to the body of the insect, it has to go to a receptive flower to receive it and pollinate the stigma so that it can germinate and grow a pollen tube that produces fertilization. In reality, the insect is not going to pollinate but to obtain nectar and pollen, but in passing it transports the pollen without realizing it.

 

How many types of pollination are and which is the most effective in growing Hass?There are different types depending on the plant species. The most frequent is the entomophilous (by insects); the second in importance is the anemophilous (by the wind). But there are many other vectors, such as hummingbirds, some terrestrial mammals or bats, as in the case of the one that is pollinated by fruit bats that enter those large, night-opening flowers. Even in aquatic species, water can be the vector that transports pollen. In any case, they are exceptions, pollination in plants is fundamentally by insects and by the wind.For the cultivation of Hass avocado, without a doubt, it is due to insects; various studies have been done and no other type of pollination seems to be significant. Why is it so difficult to achieve bee pollination in avocado?Apis mellifera is the most widely used pollinator worldwide for all crops, including avocado. The avocado comes from Central America and there was no Apis mellifera there until Europeans brought it in the 16th century; therefore, the avocado has evolved in its center of origin in the presence of other insects that are the ones that are adapted to pollinate this species in its original habitat, not the honey bee. The honey bee can be adapted to pollinate avocado, it can consume the nectar and pollen, which it does, but it is not as efficient a pollinator as other native American insects. Among these native American insects, the angelitas stand out, which are the Meliponas, bees that also build a kind of hives, they are a little smaller than the Apis mellifera, and some of these species are present in the flowers of the avocado. But there are many more species, such as numerous species of Diptera that also go to the avocado flower, including Coleoptera, some butterflies, among others. The honey bee is a very territorial insect that can become aggressive with the rest of the pollinating species; therefore, when there is a large bee population that is introduced by man, it can displace other native insects that are more effective at pollinating the avocado flower. Why do some flowers produce fruit and others do not?The avocado fruit is a fruit that requires a lot of energy to form; It is a huge effort for the plant to produce an avocado fruit and the plants do not want to produce fruit per se, what they want is to reproduce, to disperse their genes. For a plant like the avocado, it is much easier to spread its genes by producing pollen grains, which are very small and have almost no energy consumption, than by developing a fruit. What the avocado does is produce many flowers to produce pollen, and of those flowers very few can produce fruit. What we must do is change that nature of the avocado so that it produces more fruit per tree, and so we are investigating how to manipulate it to make that happen.

 

What should be taken into account in Colombia to contribute to effective pollination?What should be done is to study each site to see which native insects can pollinate the avocado. What I have seen here in most of the avocado plantations is that they are very close to the wild forest, and no chemicals are applied there, so there is a very interesting population of different native insects that can approach the avocado to pollinate and then continue their biological cycle in the native forest; therefore, it is very interesting to study this entire process to optimize avocado pollination. In addition, what they call ecosystem services is gaining more and more interest, which consist of how nature can help us produce better in agriculture and thus win both parties; Therefore, what I suggest is that you should work on which native insects help pollinate the avocado.

Why is it important that an avocado crop contains type A and B flowers on the same tree?What we have in avocado are type A and type B varieties depending on the opening and closing behavior of the flowers. The Hass variety is type A because the flower opens in the female state in the morning, closes in the afternoon and the next day it opens in the male state in the afternoon. In type B varieties such as Bacon or Fuerte, the flower opens in the afternoon in the female state, closes, and opens in the morning of the next day or two days later in the male state. So what happens in Hass: we have flowers that open today in the female state in the morning and are going to close in the afternoon; but yesterday there were other different flowers that opened in the female state and, therefore, today they will open in the male state in the afternoon. So every day we have new flowers that open in the female state in the morning and flowers that were female the day before that open in the male state in the afternoon. The flowers that open today in the female state close, but at the same time others open in the male state, and there can be an overlap between the two types of flowers and if there are insects at that time, they can carry the pollen of the female flower to the male in the same inflorescence or between inflorescences of the same tree and there would be an opportunity to produce more fruit.

How to achieve an effective fruit set in the crop?What we have seen in several countries is that a limiting factor is the lack of pollinating insects; we must work to ensure that there is a greater diversity of them and also the other thing that must be taken into account, is to be very careful with the application of chemical products; When you have problems with pests and diseases, you have to deal with chemical products, but you have to try to reduce them as much as possible or take measures so that they do not affect pollinating insects as much. Also, in some conditions it may be interesting to plant some type B trees next to Hass to increase the chances of pollination.

What is the main characteristic that determines a higher production in the cultivation of Hass avocado?Mainly to have a good management of the tree; the tree has to be well nourished; As I said before, the avocado fruit is a fruit that requires a lot of effort from the plant; then the plant must be very well nourished, otherwise what it will do when it has a stress such as lack of water, or lack of nutrients or extreme temperatures, is to throw the fruit to survive since it consumes a lot of energy. In this order of ideas, the plant must be well nourished and, of course, the flowers must be pollinated. How do you see the projection of the Hass avocado in Colombia?Very well, in fact, it has grown a lot in recent years. Colombia is a very interesting country because it can have avocado fruit throughout the year, which is very important for the market. However, a lot of work has to be done on quality, as they have different blooms there may be some very different fruits depending on the date of fertilization, but in general I see it very well.

What advice can you give to producers so that their crops are sustainable with the environment and profitable?We must try to use all the tools that nature offers  to be able to produce better; an example is the diversity of insects. We have pests and diseases, so we must try to use natural enemies as much as possible to atact them; in the case of diseases such as soil fungi, instead of applying chemical products to control them, try to have rootstocks that are tolerant to this fungus and manage the plantations well; everything we do should always be focused on depending as little as possible on synthetic chemical products; Sometimes, there will be no choice but to use them, but always in the right doses and always keeping in mind to use the most sustainable alternatives possible.

 

Any additional recommendationThe only thing I want to recommend is that we not always take the research carried out by other countries as our own, since many times these studies cannot be extrapolated to other areas; The climatic conditions of Colombia are very different from those of countries like Chile, California, Israel or Spain. Therefore, it is important to do research here, you must have information from other countries of course, but you must always try to do your own experimentation, not completely import the recipe from other countries because it may not work.

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