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USA | Vegetable Obtention
Research seeks to obtain new cold-resistant varieties of stevia Stevia comes from a tropical crop, so the objective of the research is to find varieties that can grow in colder climates to extend its cultivation, highly valued for its sweetening properties without the contribution of calories. 3/17/2021
 Making cuttings for stevia propagation at North Carolina State University/Credit:T. Wehner
It's a fact: humans generally love sugar, but for those of us who also like to watch our calories, sugar substitutes can help. Some no-calorie or low-calorie sweeteners have attracted a bad rap for containing unnatural ingredients. But there are also natural sweeteners derived from plants, such as stevia. Stevia is hundreds of times sweeter than sugar and has no calories. The global market for stevia is now worth hundreds of millions of dollars. The sweetener is derived from the leaves of the Stevia rebaudiana plant, native to Paraguay and Brazil. The leaves produce chemicals similar enough to sugar to fool the tongue. But our bodies do not burn these chemicals for fuel. Todd Wehner is a plant breeder who aims to develop stronger varieties of stevia. These best varieties can help both farmers and consumers. His research was published in Agrosystems, Geosciences & Environment, a journal of the American Society of Agronomy and Crop Science Society of America. "The market is growing rapidly as businesses and consumers move away from sugar in their diet," says Wehner. Although this tropical plant is grown all over the world, it faces obstacles growing in cold climates. Freezing temperatures can dramatically damage or even kill stevia plants in no time. That makes it harder for farmers in countries like the US to grow the sweet crop. Therefore, plant breeders like Wehner are interested in finding the hardiest stevia plants out there to help crops withstand the cold. "As we continue to select varieties that are cold tolerant in our area, new releases will be tailored to a broader growing region," says Wehner. With his teammates, Wehner recently shared his findings on the cold tolerance of different varieties of stevia. His results may help scientists grow cold-hardy stevia plants better adapted to the United States and other temperate climates. To find the strongest plants, the research team subjected 14 varieties of stevia to different cold stress tests. The tests ranged from just below to just above freezing. The plants were exposed to cold for a period of 2 to 10 days. After the stress tests, the scientists evaluated how much damage the plants suffered. A couple of varieties clearly stood out for their ability to withstand the cold. These varieties can be useful for breeders who want to grow cold tolerant stevia crops. The plants grew normally after being moved to warmer conditions. This allowed the researchers to harvest seeds for the next generation. The test temperature really mattered to measure resistance. Surprisingly, some varieties that were resistant to temperatures just above freezing were some of the most susceptible to temperatures just below freezing. That finding provides useful information on how breeders should test for cold tolerance in the future. "It seems that we will have to select the cold tolerance using a range of temperatures, so that we avoid the problems where a selection is resistant to only one temperature," says Wehner. "Testing will become a standard part of the breeding program." Wehner and his team are now providing the seeds of the most cold-tolerant varieties to any other interested researcher. Recruiting other scientists to contribute can increase the pace of stevia improvements. The team is also studying other types of crop enhancements. These include increasing seed germination, strengthening disease resistance, and improving leaf and chemical sweetener production. “We continue to develop new varieties that will have higher yields and better taste. The new varieties will be less expensive to produce as the genetics for the environments of interest are improved, ”says Wehner. "For the 95% of humans who like stevia, we continue to make these products taste better," she adds. Todd Wehner is a plant breeder at North Carolina State University. This work was supported by grants from PepsiCo's Specialty Crop Research Initiative and the United States Department of Agriculture. Source: ASA / SSSA / CSSA
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