May 4, 2020

How Does Grafting Arabica to Robusta Improve Coffee Yields?

Deforestation, soil imbalances, and pathogens are just some of the challenges that producers around the world face in growing quality coffee – which is why many adopt agronomy practices like grafting to improve their crop hardiness.

Many producers graft their Arabica scions onto Robusta rootstock to enhance the Arabica’s resistance to many of the challenges listed above. Here’s how scientists and researchers specialising in the field view grafting, as well as how the practice works for producers. 

Lee este artículo en español Cómo Injertar Arábica en Robusta Mejora el Rendimiento Del Café

How Does Grafting Benefit Coffee Plants?

To understand how grafting benefits coffee plants, two of its sections must be understood. The first is the rootstock, which is the roots and stem segments that grow underground to absorb nutrients and support the plant. The offshoots or twigs growing off a plant are called scions. Scions carry a plant’s genetic traits and characteristics and determine the fruits or flowers it will produce. 

Grafting an Arabica scion onto Robusta rootstock strengthens the Arabica’s root system, as the Robusta’s root system is bigger and stronger. As a result, the plants can absorb more water and nutrients, and will experience increased productivity and parasite resistance. It’s something that producers have done for centuries, with the first recorded coffee plant graft taking place in Java around the end of the nineteenth century. To this day, grafting is still recommended by experts. 

For insight into how grafting uniquely benefits coffee plants, I spoke to two experts – Dr Oliveiro Guerreiro Filho, a Scientific Researcher and expert on coffee plant genetics and plant resistance at the IAC (Centro de Café Alcides Carvalho) in Brazil, and Benoît Bertrand, a Geneticist and Coffee Researcher at CIRAD in France.

They both agree that one of the biggest advantages of grafting Arabica to Robusta rootstock is its ability to improve the former’s resistance to phytonematodes – something that afflicts coffee around the world. Nematodes are almost invisible worm-shaped animals that are found in their millions in soil. These creatures are bad for Arabica coffee plants, reducing coffee yield by damaging the plant’s roots and when present in high enough numbers, killing off entire plantations.

You might also like Can Fine Robusta Be Considered Quality Coffee?

What Does Grafting Involve?

Arabica to Robusta grafting usually takes place through hypocotyledonary grafting, says Benoît and Oliveiro. This method was developed in 1966 in Guatemala, and if undertaken by trained workers can be used to manually graft up to a thousand seedlings a day. The graft is made in the plant’s hypocotyl (beneath the leaf stalks and above the root) region in its early development stages. 

A cut is made below its first leaves via a small surface opening. “It is simply a matter of grafting the two plants at the ‘little soldier or butterfly stage’, using a so-called slot graft”, explains Benoît. An adhesive tape (which deteriorates over time) connects the plants to each other. 

Apoatã and Nemaya are cultivars created for use as rootstock for Arabica. “The ideal rootstock is one that exhibits simultaneous resistance to all breeds and species of pathogenic nematodes to the coffee tree”, says Oliveiro. Apoatã was created by the IAC and is used primarily in Brazil, while Nemaya is used in Central America after being developed by PROMECAFE (El Programa Cooperativo Regional para el Desarrollo Tecnológico y Modernización de la Caficultura) and CIRAD. Nemaya seeds are produced in Guatemala, El Salvador, and Costa Rica. 

Why do Arabica Plants Need Nematode Protection?

Phytonematodes are found in all plant ecosystems, and while they’re usually non-pathogenic, they can infect soil. An infection is hard to identify in its early stages as “the plants continue to produce fruits, although at a lesser rate”, says Oliveiro. This can lead to long term damage or the plant needing replacement or pruning. “The appearance of… nematodes is always a sign of soil imbalance linked to pesticide abuse (especially herbicide), deforestation, and the disappearance of organic matter”, says Benoît.

“The infestation of crops occurs mainly by planting infected seedlings. Once planted, nematodes [can’t] be eradicated. So the planting of healthy seedlings is the ideal way of prevention”, says Oliveiro. Using pesticides isn’t ideal, as Benoît says they’re “dangerous for the environment, farmers, and consumers”. Gonzalo Hernandez, a CEO and Producer at Coffea diversa in Costa Rica, has adopted grafting for this reason. “In no way did I want to use chemical nematicides due to their high toxicity, so I decided to try a much more environmentally friendly option”.

Nematodes cause an estimated 10% to 20% of losses in coffee plantations worldwide and grafting can prevent or treat it with a near 100% success rate, says Benoît, who has over 20 year’s experience researching it. Because of this, he says that grafting “should be systematic in high temperatures (lowland) and humid areas” in Central American plantations.

It’s a practice accepted by authorities like the World Coffee Research, who’ve stated that the process doesn’t impact coffee quality. Further research has also found that grafting doesn’t impact a coffee’s caffeine, fat and sucrose levels either. Oliveiro concurs that “Most of the research … state[s] that the agronomic and technological characteristics of coffee are not influenced by grafting in areas without nematodes. The same happens with caffeine levels”.

What Keeps Producers From Using Grafting?

While grafting has proven efficiency, Oliveiro says that it’s either not used, abused, or overlooked in some regions. Grafting and phytonematode study is advanced in Brazil, Latin America, and Hawaii. This is because these locations have invested in grafting education and research initiatives, as financial incentives and a suitable seed supply is present.

Grafting isn’t commonly practiced in many Asian and African producing regions – despite these areas suffering from similar threats and pesticides accounting for a significant percentage of production costs. This is often because coffee is planted in already infected soil, producing a poor result, and the fact that there are limited tolerant and viable rootstocks present, says Benoît. 

A challenge to implementing grafting in other countries is that every step – from research and soil testing to seedling transplant and monitoring – requires precise implementation. While the task itself isn’t extremely difficult, it does require training, says Oliveiro. It also requires a concerted effort over time, as “The results of bad practices can [sometimes only] be seen several years after sowing the grafted plants in the final plantation when the top part of the graft comes off the bottom”, says Gonzalo. 

Cost is a factor, as grafted seedlings cost more than standard ones. For Benoît, “one hectare represents 250 to 500 USD of the additional cost when planting one hectare of coffee (about 5 to 10% of the installation cost) – but it pays off in the long term since the plantation is established for 15 to 25 years.”

Grafting has proven benefits, and provided producers are willing to put in the required preparation, it can be worth the investment required.

Oliveiro stresses that before any grafted seedlings or cultivar seeds are purchased, the plants should be guaranteed to be certified to ensure varietal purity. He adds that any seedling producers not cultivating their seedlings or seeds in suspended nurseries while using substracts should be rejected.

The above measures – as well as consulting a soil specialist to determine your soil health, and vetting and requesting aid from your country’s agronomical institutes – will be instrumental in helping you achieve successful results when it comes to grafting Arabica onto Robusta. 

Enjoyed this? Then Read A Guide to Grafting Coffee Plants

All quotes by Oliveiro Guerreiro Filho translated from Portuguese by the writer. All quotes by Gonzalo Hernandez translated from Spanish by the writer. Photo credits: Fernando Pocasangre, The Hans R. Neumann Stiftung Institute

Please note: Before implementing the advice in this article, we advise also consulting with a local expert, since differences in climate, soil type, varieties, processing methods, and more can affect the best practices for grafting.

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