Delaware 'Sahara'
Tunisian Fulbright Scholar studying beneficial bacteria for legumes
1:06 p.m., May 29, 2012--At first glance, it wouldn’t seem like Delaware and the Sahara Desert have a lot in common. However, on closer inspection, the mid-Atlantic state and the arid regions of southern Tunisia in Africa are more similar than they first appear.
That is one reason why Mokhtar Rejili, a professor from the University of Gabes in Tunisia, is excited to be at the University of Delaware on a Fulbright Scholarship working with UD's Janine Sherrier on the study of legumes native to his home country.
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Of the similarities between the two seemingly disparate locations, Sherrier, a professor in the Department of Plant and Soil Sciences in UD's College of Agriculture and Natural Resources, explained that Delaware has sandy soil and shoreline salt stress. "Our sandy soils dry out very rapidly and our crop plants can be subject to salt stress. There are also common stresses experienced by plants grown in the two locations, albeit to different levels of severity,” she said.
The scientists are collaborating on research to identify beneficial bacteria to help the plants grow more successfully under conditions of drought and salt stress. Rejili specifically studies legumes that grow in conditions of extreme drought and severe salt stress, and his Tunisian team identifies bacteria that interact with the plant roots growing on the outskirts of the Sahara.
Sherrier is recognized internationally as a scientific expert on bacterial interactions with legumes, and together, the two scientists are working on a research project that will help farmers in Tunisia and Delaware.
The scientists are conducting research that focuses specifically on the type of beneficial bacteria that associate with legume roots and provide nitrogen to the plant. Nitrogen is an essential nutrient for plant growth, and it is often provided to the plant by the application of chemical fertilizers or manure. This is costly for growers and contributes to environmental pollution.
The beneficial bacteria studied by the team can convert a small amount of the nitrogen that is naturally abundant in the Earth’s atmosphere into a form that can meet the nutritional needs of the plant. This reduces the cost of crop production for the grower and also protects the environment from damage caused by fertilizer runoff from agricultural fields.
“The plants form close relationships with the beneficial microbes. They develop a new organ on their roots for the bacteria to reside and provide the right environment and all the energy required for the bacteria to convert atmospheric nitrogen into fertilizer," Sherrier said. "At a practical level, that means plants growing in soils without sufficient nitrogen can still have productive growth.”
Benefits to health and the environment
Rejili explained that this is especially important for extremely hot and dry areas, like southern Tunisia, where a chemical fertilizer would be of little help to the plants. Such fertilizers are often too expensive to even consider using and, worse, can be detrimental to human health.
“The fertilization of crops is limited to only the well-developed countries,” said Rejili, noting the high costs involved in producing fertilizer, only a small fraction of which is used by the plant. The remainder goes deep into the soil, where "it will contaminate the soil and the water, or it will evaporate into the atmosphere, leading to pollution," he said, adding this poses "a big question to our health.”
Sherrier said that fertilizer use doesn’t pose a health risk just in Tunisia, it does so in America as well.
“The overuse of fertilizer impacts human health,” said Sherrier, explaining that a recent Environmental Protection Agency (EPA) survey of well water quality in Delaware’s southern counties showed that more than 50 percent of the wells had nitrogen contamination above the levels recommended for drinking water and required remediation.
Sherrier said that while Rejili is interested in helping out his home country, he is also concerned about improving crop production and health for Delawareans.
“People from Delaware love their lima beans, but the beneficial bacteria are not present at very high levels in our soils. Our growers add fertilizer to ensure a good yield. That’s expensive for them, and it’s not good for our environment,” said Sherrier, adding that Rejili has taken on a leadership role on one of her projects to identify beneficial bacteria from Delaware soils that could be added to the soil early in the growth season instead of chemical fertilizer.
Sherrier also explained that the damage to the environment is not just in the fertilizer application, it’s also in the way fertilizer is made. “There’s a huge energy cost associated with making fertilizer,” said Sherrier, explaining that the process requires high pressure and high temperatures, and uses 4 percent of the world’s natural gas supply annually.
“When you burn that natural gas, it releases carbon dioxide into the atmosphere," she said, adding that there are additional environmental costs in transporting the fertilizer.
Inexpensive option
Besides the environmental and health considerations of cutting down on fertilizer use, the beneficial bacteria could also be an inexpensive option for growers, something that is of particular importance in developing countries.
“We would like to provide whatever help we can to allow the people of Tunisia to support their own food production," Sherrier said. "Food security is a huge concern for any country. This inexpensive approach to food production protects their environment and helps provide the people with a basic level of security that every human being deserves.”
Providing an inexpensive and reliable food source for developing countries is not the only benefit of this research, however. Being able to grow legumes in areas that have harsh landscapes, like southern Tunisia, will enable the growth of forage crops in areas prone to desertification. This will allow livestock to graze in the area, and will help stabilize a sandy landscape that is prone to degradation from unforgiving winds.
“If you have a few plants that can survive in that area, they can protect soils and prevent the region from converting into desert. This will help preserve the land for food or forage production,” explained Sherrier.
Beneficial bacteria
Sherrier worked closely with the U.S. Department of Agriculture (USDA) and the Delaware Department of Natural Resources and Environmental Control (DNREC) to arrange for the team to study Tunisian plants in her Delaware laboratory. For some of the species, it is the first time that these legumes will be studied outside of Tunisia.
Rejili is evaluating the diversity of bacteria associated with these plants and performing experiments to determine which ones provide the most benefits. In a laboratory setting, the team is inoculating plants with individual strains of beneficial bacteria and evaluating the plant’s performance.
“The bacteria infect the plant root," Sherrier said, "and when you talk about an infection, most people think, ‘Oh, no! You need to spray something to get rid of that.’ However, in undisturbed natural environments, the bacteria normally infect the plants, boosting their immune systems and helping the plants acquire essential nutrients. This is very similar to the benefits people gain from the bacteria which naturally reside in our digestive tract.”
Said Rejili of the plant interacting with the bacteria, “We can say they are beneficial interactions. So the plants give carbohydrates to bacteria and bacteria gives nitrogen to the plants. So there is an exchange.”
The two hope that when Rejili’s 10-month stay concludes, they can continue their collaboration. “This is a great starting point, and it’s really what the Fulbright progam is all about,” said Sherrier. “It’s helping to build bridges scientifically and culturally.”
Article by Adam Thomas
Photo by Danielle Quigley