IAEA, FAO using nuclear techniques to spot drought stress in banana plants

Whether you like your bananas slightly green or spotted, they are mostly grown in the tropics and subtropics where plants require a warm, humid climate to thrive. This is how they produce the yield that feeds the world. However, due to changing rainfall patterns and rising temperatures, bananas along with other plants suffer more and more from drought stress – a shortage of water in the root of the plant, leading to reduced harvests.

A study published this month by scientists at the IAEA and the Food and Agriculture Organization of the United Nations (FAO) as well as colleagues from Austrian and Belgian universities, highlights approaches developed using nuclear techniques for spotting and assessing drought stress in banana plants in Arusha, Tanzania. The methodologies focus on identifying the extent of the stress, which is crucial because it enables farmers to take preventive and protective action.

"The aim of this research was to shed some light onto this underexplored tropical perennial crop," said Gerd Dercon, Head of the Soil and Water Management and Crop Nutrition Laboratory at the Joint FAO/IAEA Centre of Nuclear Techniques in Food and Agriculture. "With perennial crops, like bananas, that grow over several years, the use of the stable isotope techniques has not been sufficiently and properly developed, making this study one of the first to provide practical tools, even for farmers, not only for scientists."

The scientists explored the use of stable carbon isotopes and leaf temperature as potential indicators for drought stress in banana plants. Research on other plants has shown that stable carbon isotopes and leaf temperature can be used to measure drought stress, but neither technique had been used for banana plants. Banana is an under researched crop for reasons including the complexity of its large size, long growth period, heterogenous growth pattern in which all plants grow differently even if they have the same genes, and vegetative mode of reproduction. Currently, there are no practical methods to detect drought stress in banana in the field.

However, the study found that both stable carbon isotopes and leaf temperature were highly sensitive indicators for drought stress in banana, and based on these results researchers have developed banana-tailored methods that are low-cost and therefore applicable under field conditions.

"The methods we developed can be used to test levels of drought stress and to compare different water management strategies," said Mathilde Vantyghem, IAEA/FAO PhD researcher and lead author of the study. "With such methods, local research institutes can do quick testing and eventually develop guidance for farmers to cope with drought stress."

The study is part of an ongoing project funded by the Belgian government through the IAEA Peaceful Uses Initiative (PUI). In 2022 its focus will be on scaling these methods on the slopes of Mount Kilimanjaro to identify early signs of drought stress and safeguarding action.

"The way the project is developed and implemented is very interesting: it combines Belgian expertise and research through the involvement of several Belgian universities, with expertise in the field in Tanzania and other African countries," said Caroline Mouchart, Deputy Head of Mission at the Permanent Mission of Belgium to the United Nations and International Organizations in Vienna. "Banana, in all its forms and varieties, is a very important product for a lot of countries, as a basic food and as an export product. We hope that the results of the project will benefit a lot of countries and will contribute to global efforts to promote resilient agricultural practices, better suited to climate change."

Based on the study's findings, through the IAEA's technical cooperation programme training will be provided to research and farmer intermediaries on how to use these techniques to identify early signs of drought stress and improve their agronomical practices for banana cultivation.

THE SCIENCE

All plants absorb carbon dioxide (CO2), and then create sugar from it with the help of water and light through photosynthesis. CO2 consists of one carbon atom and two oxygen atoms. Most carbon atoms in the world have twelve neutrons (12C), but half a percent of all the carbon has thirteen neutrons (13C), which is slightly heavier. 13C and 12C are thus two different versions of carbon, which are called the stable isotopes of carbon.

When plants absorb CO2 from the air, they discriminate against CO2 with 13C. Because of its heavier weight, CO2 with 13C gets absorbed more slowly by plants than CO2 with 12C. Therefore, plants favour 12C.

When drought stress occurs, plants close their stomata – the little openings in the leaves through which they take in CO2 from the atmosphere – because they do not want to lose the water that they have already accumulated. Since no more CO2 can be absorbed through the now closed stomata, the plants will be less selective and will use any CO2 that has already been ingested for photosynthesis, including the CO2 with the 13C atom. This means that when, later on, the amount of 13C in a plant leaf is analysed, one can detect if the plant was stressed or not: If plant A has more 13C in its leaves than plant B, plant A was more stressed. This is the principle of using stable carbon isotopes as an indicator of drought stress.