When it comes to improving alfalfa, plant geneticist Edwin Bingham believes the job takes persistence. Bingham has become single-minded you might even say persistent in advocating for greater persistence as an agronomic virtue in alfalfa.
Alfalfa stands that can remain productive into a ripe old age allow farmers to spread establishment costs over more years, while providing their cows with a reliable feed supply. With a persistent variety, farmers also have fewer weed control problems, less soil erosion and they can take greater nitrogen credits when they plow down a stand.
“A persistent variety needs both winter-hardiness and pest resistance, but these traits alone don”t ensure stand longevity,” says Bingham, an agronomist at UW-Madison”s College of Agricultural and Life Sciences. “Persistence has a genetic basis, and my breeding program focuses on persistence by applying selection pressure to rebuild and maintain it.”
Bingham says alfalfa lost some of its persistence while plant breeders were selecting for other traits in the 1970s and 1980s. One of Bingham”s students analyzed 30 years of Wisconsin Alfalfa Variety trials and found that multiple disease resistance in many newer varieties was not always contributing to persistence. Also, there was evidence that Vernal, a 35-year-old variety, was persisting better than many newer varieties.
Bingham turned to Vernal as the genetic base for rebuilding persistence. He used a special Vernal population from Spooner, Wis., which had demonstrated its persistence through nearly five decades of Wisconsin winters. In the late 1980s, Bingham had already begun efforts to cross Vernal with partial inbreds from selected commercial sources that could strengthen the new plants” resistance to root rot and verticillium wilt.
The initial result of Bingham”s efforts to rebuild persistence was Columbia 2000, so named because it was developed and tested in Columbia County, Wis. The variety was released through the Wisconsin Crop Improvement Association in 1996.
Tests of the new variety began in 1990 and 1991. In those tests in seven states, Columbia 2000 yielded about 10 percent more than Vernal, according to Bingham.
“What we liked about Columbia 2000 in the early tests was the way it rose in rank in several Midwest trials during the years of testing,” Bingham says. “This meant that varieties that ranked higher in yield in the first year or two of testing were falling off while Columbia 2000 persisted.”
Bingham cites several examples:
* In Rosemount, Minn., Columbia 2000 rose from tenth of 63 entries in the first year to fourth in the fourth year.
* At Chatham, Mich., Columbia 2000 rose from eighth out of 10 in the first year to second in the fourth year.
* At Arlington, Wis., the 1990 and 1991 generations persisted through two of Wisconsin”s most severe winterkill winters in Bingham”s nurseries. “Many varieties decreased dramatically during the past six years at Arlington, but Vernal, Columbia 2000 and a few others have persisted,” Bingham says.
The key to rebuilding persistence, according to Bingham, is selecting for the trait as the last step in breeding rather than the first.
In his breeding program today, Bingham is selecting parents for higher levels of pest resistance but then putting them in persistence trials for at least five years before selecting parents of new varieties.
“Our experience suggests that the only way to ensure persistence is to select for persistence in the field,” Bingham says. “The history of alfalfa breeding contains many examples of quick tests for this or that trait, including persistence. Such tests have come and gone. Some of them may have contributed to the erosion of persistence in the 1970s and 1980s. Therefore, we are going to do it the old fashioned way selecting parents that have persisted in the field for years.”