It has dominated the Southeast peanut variety realm for the past two years, known primarily for its resistance to the dreaded tomato spotted wilt virus. But now, the same trait that made Georgia Green famous may threaten its reign.
“From Andalusia west, Georgia Green is working fine,” says Dallas Hartzog, Auburn University Extension agronomist. “The problem is in the eastern half of the Peanut Belt where tomato spotted wilt is affecting Georgia Green adversely.”
Long-standing peanut production is the reason for the high incidence of tomato spotted wilt virus in the southeastern part of the Peanut Belt, says Auburn University plant pathologist Austin Hagan. “The virus is more entrenched in areas traditionally known for peanut production. There isn't as much tomato spotted wilt in areas new to peanut production.”
Hagan says the number of virus-carrying thrips in those areas has overwhelmed the previous resistance of Georgia Green to the virus. “We're at a point now that growers have to look at alternate peanut lines as the next line of defense against tomato spotted wilt.”
The main contenders to replace Georgia Green are the mid-season cultivars of Georgia-02C, Carver, AP-3 and ANorden, according to Hagan. “These are the strongest candidates right now. Research has proven that they exhibit considerably less tomato spotted wilt than Georgia Green.”
Dan Gorbet, professor of agronomy at the University of Florida, has successfully experimented with these and other varieties in search of disease-resistant alternatives to Georgia Green. “We've released quite a few new varieties, including Andru II, ANorden, Carver, AP-3, Hull and DP-1 that exhibit the same disease resistance as Georgia Green, and in some cases, better resistance,” Gorbet says.
Both Gorbet and Assistant Professor Barry Tillman say they favor AP-3 and the University of Georgia release, Georgia-02C, as the most resistant medium maturity varieties. “They have very high yields, good grades and good resistance to white mold,” Tillman says.
In addition to Georgia 02-C, one of the most recent releases by peanut breeders at the University of Georgia is Georgia-03L, a large-podded variety with a high level of resistance to tomato spotted wilt virus and moderate resistance to soilborne diseases. “Georgia-03L combines disease resistance with large pods, medium maturity and excellent yields,” says University of Georgia peanut breeder Bill Branch. “It has very good stability and a wide range of adaptability throughout the major peanut production areas.”
Some researchers say there is no explanation for the apparent breakdown in resistance to the virus. “Why Georgia Green is having problems, we can't really say,” Hagan says. “There is not much difference in the genetic resistance package in Georgia Green and in those of the newer lines.”
But University of Georgia Extension Agronomist John Baldwin says the problem lies not in the Georgia Green variety itself but in poor management. “I don't think Georgia Green is becoming less resistant to tomato spotted wilt. Variety is one of the most important things to consider with tomato spotted wilt virus, but management practices also should be emphasized.”
While proper tillage systems, controlling insects, and row spacing may reduce the prevalence of tomato spotted wilt virus, Baldwin says one of the most important practices farmers must fine tune is planting date. “Some farmers are having problems because they are not following the University of Georgia Tomato Spotted Wilt Virus Risk Index and are planting too early.”
Growers should consider these and other factors first before planting a different variety, Baldwin says. “Some varieties that show improved tomato spotted wilt resistance are late maturing and may interfere with your cotton crop. Also, if you plant in May, you may suffer from frost damage. And, if the peanuts don't mature, it reflects in yield and grade.”
Despite the availability of different variety types, Hartzog says he still doesn't expect a dramatic shift in variety use in the next two or three years. “There may not be one dominant variety in the future. It's like Ford and Chevrolet — each man has his reasons for preferring one or the other. Each has its good and its bad characteristics. Only when these varieties are grown on a large scale will we see which ones will be dominant.”
Hartzog says the best advice he can give farmers is to avoid drastic changes such as converting all of their acreage to one variety. “The best thing a farmer can do is identify which varieties fit best in each situation and plant more than one variety.”