Improved peanut varieties lead fight against diseases

Varieties have become an increasingly important weapon in the Southeastern peanut grower’s continuing battle against diseases. Nowhere is this more true than in the lower Southeast, where growers spend millions of dollars each year controlling and attempting to prevent a myriad of peanut diseases.

Varieties such as the tomato spotted wilt virus-resistant runner-type Georgia Green have been credited with rescuing peanut farmers from devastation in states such as Georgia, Alabama and Florida, and varieties with even greater disease resistance are making their way through the research pipeline and onto the market.

According to University of Georgia Plant Breeder Bill Branch, the first and most important step growers should take to control diseases, especially tomato spotted wilt virus (TSWV), is to plant a resistant variety.

“It’s extremely important that peanut growers choose resistant varieties and plant high quality seed to insure an adequate stand for growth and development,” he says. “Planting a high quality plant material with good germination during the recommended planting time will help compensate for any potential losses.”

In addition, Branch says having an adequate stand early in the season is vital. “It is very critical to have an adequate stand to start out with in order to end up with at least four plants per foot at the end of the growing season. We recommend planting six seeds per foot of row,” he says.

While no variety of peanut is immune to the ravages of such diseases as TSWV, a few have consistently demonstrated moderate levels of resistance. In addition to resistance, some varieties appear to have some degree of tolerance as well. Higher levels of resistance and tolerance are anticipated since peanut breeding programs are now evaluating potential new varieties for response to tomato spotted wilt virus.

Peanut varieties also can have a major impact on fungal disease. The variety Georgia Green currently is planted on the majority of the peanut acreage in the Southeast. However, new varieties from breeding programs at the University of Georgia and the University of Florida not only have improved resistance to spotted wilt but to fungal diseases as well.

For example, the varieties DP-1 and Georgia-01R have some of the best leafspot resistance ever available in commercial varieties. Varieties Georgia-02C and Carver have a level of resistance to cylindrocladium black rot (CBR) that is superior to that of Georgia Green. Just as none of the current varieties is immune to spotted wilt, none is completely immune to fungal diseases either. However, improved resistance will likely lead to reductions in disease severity.

It is important to remember that improved resistance to one disease does not mean that the variety also possesses superior resistance to other diseases. For example, DP-1 and C99-R have greater resistance to leaf spot than Georgia Green. However Georgia Green has greater resistance to rhizoctonia limb rot.

“Rhizoctonia limb rot disease pressure fluctuates from year to year and field to field, but it can be a major problem depending on growing conditions,” says Branch.

Producers in the lower Southeast will have approximately 10 peanut cultivars to choose from to plant during the 2005 production season, according to University of Georgia Extension specialists. In 2004, seed of 14 cultivars were planted, but several have been dropped for this year. It is best, say Extension specialists, to consider all factors — disease resistance, maturity, seed availability, marketability — when selecting which cultivars to plant in 2005.

Seed are expected to be available for the following cultivars in the lower Southeast this year: Georgia Green, Georgia-03L, Anorden, Andru II, Georgia-02C, C-99R, Tifrunner, Georgia-01R, Carver and AP-3.

For some of these cultivars, the seed supply will be limited. These include Georgia-03L, AP-3, and Tifrunner. There is the possibility that there may be seed of ViruGard and Hull.

Georgia Green is a TSWV-resistant runner-type peanut variety released in 1995 by the Georgia Agricultural Experiment Stations. Georgia Green is highly productive and has very good stability across many different environments. In state yield tests conducted at multi-locations in Georgia during 2003 and 2004, Georgia Green was found to have a higher yield, grade, and dollar value return per acre than four other new medium maturing runner-type varieties: AP-3, Carver, Andru II, and ANorden. After more than a decade of research tests, Georgia Green still maintains a stable high level of resistance to TSWV. It also has a high level of rhizoctonia limb rot resistance, which most other varieties do not. It has a medium maturity, which is about two to three weeks earlier than the later maturing runner varieties.

Georgia-01R is a new multiple pest resistant runner-type peanut variety that was released in 2001 by the Georgia Agricultural Experiment Station. Georgia-01R has shown good resistance to TSWV, both early and late leafspots, stem rot or white mold, CBR, and leafhoppers, which should be beneficial in lowering production costs. Georgia-01R has late maturity and spreading runner growth habit as do these other varieties, and it has a larger seed size.

Georgia-02C is a new high-oleic runner-type variety that was released in 2002 by the Georgia Agricultural Experiment Stations. Georgia-02C can have later maturity than Georgia Green with seed and pod size slightly larger. It also has the high oleic and low linoleic fatty acid oil chemistry with spreading runner growth habit similar to AgraTech 201. Georgia-02C has excellent TSWV resistance as well as CBR resistance.

Georgia-03L is a new large-podded runner-type peanut variety that was released in 2003 by the Georgia Agricultural Experiment Stations. Georgia-03L has similar maturity as Georgia Green with pods and seed significantly larger, requiring more calcium. Georgia-03L also has a high level of resistance to tomato spotted wilt TSWV and moderate resistance to soilborne diseases white mold or stem rot and CBR.

Andru II is an early maturity variety but not as early as Andru 93 or ViruGard. Because it has high oleic oil chemistry, excellent TSWV resistance, and good white mold resistance, it will probably replace Andru 93 as an important early maturity variety. Anderson Peanut Company is the major supplier of Andru II seed.

ANorden is a medium maturity variety, with good TSWV resistance and high oleic oil chemistry. ANorden has the same level of resistance to white mold, leaf spot, and rhizoctonia limb rot as Georgia Green. ANorden will be a replacement for SunOleic 97R.

AP-3 is a recent release by the University of Florida that has been licensed to Anderson Peanuts. It is a sister line to Carver. AP-3 has excellent resistance to TSWV and white mold, the highest available in a medium maturity variety. Yields and grades were very good at Marianna and Gainesville.

Carver is a medium maturity variety with good resistance to TSWV and white mold. It has some resistance to CBR and rhizoctonia limb rot. Carver has good yield potential. A good leafspot spray is needed for this variety.

C-99R has been one of the higher-yielding entries in tests at multiple locations, and usually ranks as one of the best in resistance to TSWV. C-99R has resistance to leafspot, white mold, rust, and has a small amount of resistance to CBR. It is a late-maturing variety with large seed, and calcium needs are similar to a Virginia type.

Hull is a late maturity, jumbo runner seed size, and high oleic variety with good to excellent resistance to TSWV, late leaf spot, and white mold. It also has good resistance to CBR and some resistance to root-knot nematodes.

ViruGard was released by AgraTech Seeds in 1997. It has resistance to TSWV and has produced good yields. ViruGard varies in maturity, being 125 to 135 days. This may be due to weather conditions, but growers of this variety should be sure to use the hull-scrape or peanut maturity profile method of predicting maturity.

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