trol drought tolerance in soybeans. Persevering in that
Soybean Researcher Hunts Genetics Of Drought Tolerance From The Air L
FAYETTEVILLE, ARK.
arry Purcell counts on clear skies to find the genes that con-
search, Purcell has iden- tified regions on soybean chromosomes associ- ated with drought toler-
ance, providing soybean breeders with a valuable tool for developing im- proved crops that can thrive when water gets scarce. Purcell
guished Professor of crop physiology for the University of Arkansas System Division of Agri- culture. He is also
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holder of the Altheimer Chair for soybean re- search at the Arkansas Agricultural Experiment Station, the division’s research arm, and the Dale Bumpers College of Agricultural, Food and Life Sciences at the Uni- versity of Arkansas. Soybeans
are
Arkansas’ leading row crop, bringing in $1.36 billion in cash farm re- ceipts in 2018, accord- ing
to i the 2020
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n e :
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agement and irrigation technology allowed soy- bean breeders to focus on improving yields, dis-
tolerance tend to reside mostly in very old vari- eties, known as lan- draces, that were grown in east Asia locales hun- dreds or thousands of years ago, Purcell said. These landraces are maintained in the USDA Soybean Germplasm Collection, and while some of these ancient varieties have drought tolerance, they also have low yields. “We contend that there
are favorable genes for drought tolerance,” Pur- cell said. But in the past, not much effort was expended trying to locate them. Purcell set out to iden-
tify landraces with the genetic traits that con- tribute to drought toler- ance.
That meant
needed. First, he sought out
physical traits of soybean plants that
indicated
drought resistance. His research pointed him to four such characteristics — late wilting, above-av- erage nitrogen fixation, water-use efficiency, and cooler
than average
canopy temperature. The first, late wilting,
means the plants’ leaves endure more prolonged drought conditions be- fore the leaves begin to curl up for lack of mois- ture. Purcell hypothe- sized that late wilting indicated more efficient use of water than the av- erage soybean plant. Years of research data backed him up. The second character- istic, nitrogen fixation, is
Purcell said that all
plants need water for growth through photo- synthesis, but that evo- lution has led to different strategies for how effi- ciently plants use water. During the day, as pho-
tosynthesis takes place, transpiration moves water through the plant and out through tiny openings called stomates in the leaves. Evapora- tion drives the process and cools the canopy leaves. In general, plant water-use is least effi- cient during the hottest part of the day when evaporative demand is highest. As water becomes less
available under drought conditions, soil moisture content decreases in plants,
transpiration
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A close up image of soybean test plots showing the relative temperature of four plots. The numbers do not indicate actual temperature
but are units of relative difference. The coolest plot shown has a relative temperature of 59 and the hottest plot has a relative temperature of 78 or a difference of 19 relative temperature units. This corresponds to a temperature difference of 1.7 degrees Fahrenheit. Photo courtesy of Larry Purcell
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ease resistance and food quality, Purcell said. But changing climate has in- creased stresses on water quality and quan- tity, and that has ele- vated the importance of developing soybean vari- eties with drought toler- ance. “Drought is the num-
ber one environmental factor that limits yield in soybeans,” Purcell said. Genetics for drought
screening hundreds of these ancient varieties, some of which might have potential to be crossed with high yield- ing breeding lines that would combine those de- sirable traits. Botanical action Finding a way to ac-
complish such a monu- mental task led Purcell down two research paths whose intersection would provide the tool he
a feature of legumes, in- cluding soybean plants. They have a symbiotic re- lationship with certain microbes in the soil that convert nitrogen gas into a form of nitrogen that the plants can use for nutrients. Nitrogen fixa- tion is essentially a process by which soy- bean plants, assisted by symbiotic soil microbes, make their own nitrogen fertilizer.
slows or ceases, and the leaf canopies become warmer, Purcell said. But plants with higher
water-use efficiency par- tially close their stomates during the heat of the day, retaining a water re- serve in the soil. Under drought
these plants have access to water that less effi- cient plants do not. They can maintain transpira- tion and remain cooler.
conditions,
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