Joining a high-yield pepper plant sapling to the roots of a strong and resistant variety could help pepper farmers cope with lower rainfall, a study has found.

An experiment using the technique of merging two plants, known as grafting, resulted in higher fruit yield during periods of less rain. Plants also grew much better in salty soil, a by-product of drought, the researchers found. The results of the study were published last month in Scientia Horticulturae.

Peppers are native to Mexico, but are grown in many developing countries – both as the bell pepper vegetable and chili pepper to make spices. The plant is a particularly important commercial crop in Latin America and Asia. Around 26 million tons of peppers were grown commercially around the world in 2007.

“Grafting allows for the combination of the desired shoot characteristics with roots that can overcome environmental stress”

Angeles Calatayud

The Spanish research team took saplings of commercially grown Adige Lamuyo peppers and grafted these onto wild peppers. They also grew the pepper on its own as a control group. For the third part of the experiment, the researchers grew the grafted and original plants outdoors in one normal field and one with salt and irrigation problems.

The research showed that peppers grafted onto Capsicum anuum, a wild pepper plant, were much better at dealing with drought conditions and high levels of salt in the soil. The yield of the grafted plants was 40 per cent higher than that of the ungrafted plants grown from seed.

“Pepper grafting could become an environmentally friendly adaptation strategy,” says Angeles Calatayud, a researcher at the Instituto Valenciano de Investigaciones Agrarias in Valencia, Spain, and co-author of the paper. “Grafting allows for the combination of the desired shoot characteristics with roots that can overcome environmental stress.”

Grafting is done by cutting a plant off near the root, shaping its stalk into a wedge and fitting this into a matching groove on the severed stem of another plant. The technique is used for many other vegetables as a means of dealing with stress factors such as extreme climate conditions and toxic soil. Grafting is common in the farming of watermelon, tomato and cucumber. In Spain, almost all watermelon are grown from grafted plants.

Grafting is ideally suited for developing countries, the researchers say, as the technique does not require expensive kit or expertise. They described Capsicum anuum  as “priceless plant material” for the sustainability of pepper farming.

However, there are costs implications to the technique, says James Nienhuis, a plant breeding researcher at the horticulture department of the University of Wisconsin-Madison in the United States. He points out that in Costa Rica, for example, a conventional seedling costs around $0.20, but a grafted seedling could cost up to $0.75. This is because the grafted plants require extra work, and result in half of each plant being thrown away.

“But, the extra cost of the seedling is saved easily by eliminating the need to purchase and apply chemicals to control soil pathogens and also by the dramatic increase in yield,” he says. Nienhuis cites the example of a project he worked on in Totonicapan, Guatemala, where a women’s cooperative managed to up the yield of their tomato harvest by 50 per cent by grafting plants onto the roots of varieties that are resistant to pathogens in the soil.

The grafting technique is also used to protect plants against pests, which decreases the need for expensive pesticides. In South Asia, Edwin Rajotte, a professor of entomology at Penn State University in the United States, has studied grafting as a means to combat bacterial wilts in eggplant and pepper plants. However, he warns that grafting loses its power over time.

“Over time, pests can evolve to overcome root resistance,” he explains. “Grafting should be a component of an extensive integrated pest management approach.”