tic, cooler canopy tem- perature,


The fourth characteris- became


Purcell’s target of choice for identifying soybean breeding


lines with


drought-tolerant genet- ics. Early on,


identifying


breeding lines with lower canopy


temperatures


was laborious work, wad- ing through test plots, measuring canopy tem- peratures with handheld infrared thermometers. Purcell said the sun, air temperatures, and other environmental conditions cause canopy tempera- tures to rise and fall throughout the day. Because these condi-


tions can hamper the re- search, Purcell needed to measure canopy temper- atures of hundreds or thousands of plants very quickly, before the va- garies


changed the results. This need for speed led


Purcell down the second research path — remote sensing using aerial drone-mounted cameras. Taking flight Purcell first used an


off-the-shelf DJI Phan- tom 4 drone with color cameras to measure plants’ nitrogen content based on green shades in their canopies. (See re- lated


story:


https://bit.ly/AAES-soy- beanDGCI.) To measure canopy temperatures, he adopted infrared imaging to see if they could collect usable data. It turns out they could.


And as compact infrared cameras improved, so did Purcell’s results. With a high-quality


infrared


camera mounted to an off-the-shelf consumer drone, he can measure differences in canopy temperature down to one-tenth of a degree Fahrenheit. “High-resolution in-


frared imaging from a drone offers rapid, accu- rate and non-destructive monitoring of a large number of experimental fields,” Purcell said. Because soil tempera-


tures on a sunny day can climb more than 20 de- grees higher than the air temperature,


waited until the soybean canopies were


Purcell fully


closed before he began scanning the plants from the air. “Soil temperature can mask canopy tem- perature,” he said. Once the canopies were


closed, Purcell and grad- uate student Sumandeep Bazzer measured canopy temperatures of 168


breeding lines developed from crosses between parents that differed in their sensitivity of nitro- gen fixation to drought. Purcell and Bazzer con- ducted their experiments at two Agricultural Ex- periment Station loca- tions — Pine Tree Research Station, be- tween Wynne and For- rest City, and Rohwer Research Station, southeast


of


Dumas. They col- lected data from those plots over three years. “It takes about


five minutes to scan about 350 plots from the air,” Purcell said. “But analysis of images is time-consum- ing.” With multiple replications


of of weather


each of the 168 breeding


lines


planted in dupli- cated test plots in two research loca- tions and captur- ing five to 10 infrared images of each plot, Purcell and Bazzer had thousands of im- ages to evaluate. S o f t w a r e


(https://bit.ly/t urfanalyzer) devel- oped by Purcell’s son, Carlin, over- lays grids on the images to identify the test plots. The software extracted temperature data from all the pixels in each grid and identified


the


breeding lines with cooler canopies. The


research


was supported by the United Soy- bean Board and Arkansas soybean producers with funding adminis- tered through the Arkansas Soybean Promotion Board. Scientific Reports, a Nature publica- tion, recently pub- lished results of the


study:


h t t p s : / / b i t . ly/aaes-CanopyIR Genetic cartog-


raphy After identifying


the most drought- tolerant breeding lines,


wanted to identify genetic markers for the traits that contribute to a cooler canopy. The


difficulty


with traits like canopy tempera-


January 15, 2021 www.mafg.net / MidAmerica Farmer Grower • 13 Purcell


ture is that they are de- termined by the action of many genes scattered across different chromo- somes. Identifying these chromosome locations, referred to as loci, asso- ciated with cooler canopy temperatures


during


drought is particularly difficult, Purcell said. “There’s not a single gene that controls drought tol- erance,” he said.


Working with collabo-


rators at the USDA and other Land Grant Univer- sities, Purcell used ad- vanced gene mapping tools to identify loci asso- ciated with drought tol- erance traits. “We used different


methods to identify and confirm some genes that have been identified in earlier research, and also some novel genes


that were not caught be- fore,” Purcell said. It was a lengthy


process that took years, but Purcell said his team had identified 34 markers in previous re- search that are associ- ated with cooler leaf canopies under drought conditions. Working with Bazzer, Purcell identified 11 more loci for canopy temperature.


Of these 11 loci, nine were associated with loci for delayed canopy wilt- ing; this indicates that loci that contribute to delaying wilting also contribute to a cool canopy. Pyramid scheme The end game of all


this work is to give soy- bean breeders a set of tools that they can use


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