Q&A: Mutant Fruit Trees to Grow in Saline Soils in Cuba

By Ivet González Reprint | | Print | |En español

Ivet González interviews ORLANDO COTO of Cuba’s Tropical Fruit Research Institute

Many people in Cuba have avocado trees in their yards, for family consumption. Credit: Ivet González/IPS

HAVANA, Dec 20 2012 (IPS) - During some parts of the year, a layer of salt can be seen on the ground in eastern Cuba, which makes it difficult, and sometimes impossible, to farm. Since agronomist Orlando Coto saw this with his own eyes, he has been searching for salt-tolerant fruit trees.

“The main causes of this phenomenon are associated with climate change, like drought and penetration by seawater,” said Coto, of the governmental Tropical Fruit Research Institute (IIFT). “Alternatives have to be found that come up with faster results than the traditional plant breeding techniques, to deal with this problem.”

Coto, a university professor, discussed with IPS the extent of the problem of saline soils in Cuba and a project of induced mutation to produce cultivars of avocado and citrus trees that would be more resistant to hostile conditions.

Q: What is salinisation of the soil? What causes it?

A: It’s the concentration of salt in the soil, a complex problem that has multiple causes. It can be caused, for example, by drought, whether due to lack of rainfall or high temperatures, the penetration of the sea in low-lying areas, the availability of nutrients in the soil, or the contamination of the aquifers because of the overuse of agrochemicals.

In the case of Cuba, the main causes of salinity in the soil are the lengthening of the dry periods and seawater intrusion, factors associated with climate change. As the amount of water available in the soil declines, the concentration of compounds like sodium and chloride – which are naturally found in the soil separately, but together make up salt – increases.

For that reason, farmers would welcome new cultivars of all kinds, especially fruit trees, that are tolerant of salinity and drought, and that would make it possible to save water and to use other irrigation methods.

Q: What parts of Cuba are hit hardest by this phenomenon?

A: Soil salinity is bad in the entire southern stretch of Guantánamo (at the eastern tip of the island), because of drought and because it’s very low-lying land, and the seawater penetrates through the aquifers. The entire southern portion of eastern Cuba is dry and thus tends to have high levels of salinity.

In this country, we don’t have any extremely dry or saline areas. The ones that have the driest, most saline conditions are the abovementioned part of Guantánamo and the region north of Santa Clara (east of the Cuban capital). The latter has a kind of clay in the soil that creates lumps, which make it difficult for plants to absorb water and nutrients.

In the 1990s, I took part in a multidisciplinary study carried out in the south of Guantánamo, where rapid changes were detected in the salinity of the soil, and in a smaller area, very different – that is, contrasting – concentrations of salt were found.

Q: What challenges does this ever-changing reality pose for research into new saline- and drought-resistant varieties?

A: So-called precision agriculture, which consists of applying scientific-technical advances in much more localised areas to obtain specific results for small farmers or agricultural businesses, is gaining more and more ground.

On the other hand, science requires time to come up with solutions, while the changes and the effects of climate change on crops are occurring faster and faster.

Q: What does the search for more tolerant varieties imply, in the case of fruit trees?

A: Fruit trees have specific requirements. Crossbreeding is nearly impossible, because of biological limitations, as can be done in the case of vegetables. In addition, they have a long juvenile period. Orange or avocado trees do not start producing until they are three or five years old on average.

Only after resistance has been transmitted for three generations (in vitro or in the countryside) can it be stated that a new cultivar has been found. In the IIFT we have been experimenting since the last decade with irradiation and in vitro culture of avocado seeds, through a method aimed at accelerating fruit improvement programmes.

Q: What are the goals of the study? Who participated in it?

A: We have worked since 2000 with the Centre for Technological Applications and Nuclear Development and the National Institute of Agricultural Sciences, among others in Cuba, and with financing from the International Atomic Energy Agency, which is supporting the search for solutions against climate change in agriculture, specifically in terms of drought and salinity.

We started with the irradiation of avocado seeds, to obtain mutant seeds that might possibly be resistant to drought, salinity and a disease (Phytophthora, a group of plant-damaging pathogens) that affects the roots and the trunk of avocado trees, or others like papaya and orange trees.

We chose the only kind of avocado stock used commercially in Cuba. Lately we have incorporated citrus trees in the research in which induced mutation techniques are applied.

Q: How much progress have you made? How much longer will it take?

A: It has been a long process, but we already have the half-lethal dose of radiation to apply on seeds and buds, and we have also adapted an international methodology for improving avocados to our conditions here.

We have established an in vitro selection system where we simulate the average conditions of drought and salinity found, for example, in some soils in southern Guantánamo.

A group of possible mutants were obtained – they’re currently in the study phase – which in the in vitro conditions showed certain levels of tolerance of salinity. But it will still take at least seven years to obtain a cultivar.

Q: What problems to be solved has your centre identified, in order for Cuba to be able to meet local demand for fruit?

A: The main problem is the availability of high-quality, certified seedlings for the entire community of farmers. More knowledge about their cultivation also has to be disseminated through pamphlets and other printed materials, to which small farmers would have better access.