Fall-Seeding Alfalfa Can Be Risky
As many southeastern and south-central growers have come to know,
establishing a fall stand of alfalfa can be a major headache when the fungus
Sclerotinia trifoliorum lurks in soils.
In the cooler, moist conditions that follow hummer's heat, this fungus can
devastate a new alfalfa stand by causing rots that kill seedlings before they
A legume that fixes its own nitrogen, alfalfa is grown as a high-protein hay
and forage crop for livestock. But in such south-central states as Kentucky and
Missouri, the very threat of a Sclerotinia outbreak can discourage
growers from even attempting a fall seeding.
"There are plenty of growers who've successfully done it," notes
plant pathologist Paul Vincelli, of the University of Kentucky in Lexington.
"But by the same token," he adds, "there are also a lot of
growers who say they'll never try it again."
Currently, no commercial alfalfa cultivars possess resistance adequate to
withstand a full-blown Sclerotinia assault, Vincelli says. But he and
other researchers who study the disease are keeping close tabs on new alfalfa
germplasm called Mississippi Sclerotinia-Resistant, or MSR.
The first of its kind, this resistant germplasm could supply valuable
"genetic ammo" for breeding new commercial cultivars.
"MSR has a higher level of resistance than any of the 26 commercial
cultivars we've compared it with so far," says ARS plant pathologist
Robert Pratt in discussing lab and field studies made since 1991. "My hope
is that the germplasm will serve as a resistant standard, or benchmark."
Pratt, along with plant breeder Dennis Rowe and lab technician Mark Stokes
of ARS' Forage Research Unit at Mississippi Slate, Mississippi, produced the
MSR germplasm. Earlier efforts to devise screening techniques for identifying
Sclerotinia resistance in alfalfa and other legumes led to the team's
development of MSR, says Pratt.
After searching among nearly 2,000 individual plants of the commercial
cultivar Delta, the researchers propagated the most promising candidates. They
then crossed and screened the plants several times over, using new techniques,
to strengthen the resistance trait in the MSR progeny. MSR has so far withstood
lab inoculations of Sclerotinia strains collected from diseased plants
in Wisconsin, Ohio, Pennsylvania, Louisiana, and Georgia. However, Pratt
cautions, a truer measure of its fungal resistance will come with field tests
in those states.
One researcher interested in the ARS germplasm is extension plant
pathologist Erik Stromberg, who is at the Virginia Polytechnic Institute in
Blacksburg. He hopes to test MSR against Sclerotinia in Virginia's
western and Piedmont regions.
About 100,000 acres of alfalfa are grown theremuch of it in old fescue
pasture that can harbor the fungus. Combined with other preventive tactics,
says Stromberg, planting resistant cultivars "would take much of the risk
out of getting the alfalfa established."
Ohio State University plant pathologist Landon Rhodes also points out
potential benefits to growers in northeastern and southern Ohioareas
where hilly terrain characterizes much of the alfalfa acreage. In such regions,
farmers practice no-till to protect soils from eroding.
However, says Rhodes, leaving the soil unturned can promote fungal infection
of alfalfa standsespecially in the fall. By Jan Suszkiw,
E. Rowe are in the USDA-ARS
Science Research Lab, 810 Highway 12 East, Mississippi State, MS 39762;
phone (662) 320-7386.
"Fall-Seeding Alfalfa Can Be Risky Business"
was published in the December 1995 issue of
Agricultural Research magazine.