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Hope is Waiting in the Weeds

Could grain sorghum steal johnsongrass’ secret to longevity?

Col. William Johnson had no clue he was dancing with the devil in 1840. Big hopes and a bag of seed in hand, he planted an invasive weed as a forage crop on his Alabama farm. The coarse and clumping weed was already present on U.S. soil, tagged with a variety of names, but with his premier planting, johnsongrass stuck as the official name. More than 175 years later, scientists are making use of Johnson’s folly.

Stan Cox, senior research coordinator and scientist at The Land Institute, and Andrew Paterson, plant geneticist at the University of Georgia, are crossing friend and foe, combining grain sorghum and its outcast cousin johnsongrass to create multi-crop sorghums from single plantings through ratooning or true perennial production. Banking on johnsongrass’ wide adaptation, they are using it to improve cold and drought tolerance, as well as disease and insect resistance. 

With 20 years of sorghum research aimed at increasing the cereal’s overall drought resistance and developing perennial strains, Paterson leads a project funded by the U.S. Agency for International Development. “Repeated patterns of annual agriculture expose soil, which is our greatest natural resource, to erosion and loss of organic matter,” Paterson says.

Cox has produced several grain sorghum-johnsongrass crosses with variable progeny. Some show the ability to produce rhizomes and overwinter like johnsongrass; some have the relatively large seed and non-shattering characteristics of grain sorghum. “We’re finding all sorts of combinations,” Paterson explains. “We believe we’ll find disease-resistance genes in johnsongrass highly useful to grain sorghum. After all, johnsongrass is out there in fields surviving and showing resiliency each year.”

Johnsongrass is a robust plant, growing on every continent but Antarctica. On a list of the top 10 worst weeds, invariably glyphosate-resistant johnsongrass makes the cut. 

Paterson and Cox are searching for a balance where above-ground plant material produces yield and belowground plant material survives cold winters. “We’re trying to disarm johnsongrass and drop the noxious weed aspect but keep the perenniality,” Paterson says. “We’re not redoing a superweed. Our crosses harness a tiny portion of johnsongrass.”

Paterson has already placed speedy growth, thick stand, heavy biomass and disease resistance in his crop quiver. He’s presently targeting larger seed, higher yield and shatter resistance. “I’m very confident we’ll get all of these breeding questions worked out; it’s just a matter of time,” he adds.

The difficulty comes in selecting plants containing necessary perennial genes, yet lacking johnsongrass’ tendency of small seeds, excessive tillering and branching. “All plants have some of the good and bad genes. We take those with the most good and fewest bad, and cross them to grain sorghum. Then we repeat the process; it takes a lot of time,” Cox says.

This crop and weed marriage, however, might lead to a plant highly beneficial to soil and overall agriculture production. “Crossing and producing hybrid plants is the easy part,” Cox explains. “Achieving the ultimate goal—perennial grain sorghum varieties on a field scale to provide acceptable yields of grain—is just 15 to 20 years away.”  

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