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New varieties target peanut diseasesNew varieties target peanut diseases

October 18, 2000

4 Min Read

High yields and quality with little need for chemical disease control are the goals of North Carolina and Virginia peanut breeders.

"For the foreseeable future our primary breeding objective is to breed more complete disease resistance into new varieties to reduce the need to apply pesticides to the peanut crop," Peanut Breeder Tom Isleib told farmers attending the 48th Peanut Field Day in Lewiston-Woodville, N.C.

In the past, peanut breeders have assumed growers would use chemicals to control most diseases and other pests. This left the breeders free to concentrate on other traits, like yield, bright hulls and a high percentage of fancy and jumbo peanuts.

Falling peanut prices have forced growers to seek ways to cut back on chemical applications, relying more on crop rotations and varietal resistance to control pests.

Isleib's breeding program is concentrating on four diseases that cause significant losses most every year: early leaf spot, Cylindrocladium black rot, Sclerotinia blight and tomato spotted wilt virus. Plantings of breeding lines and commercially available peanuts at the Peanut Belt Research Station showed the progress breeders are making toward insect and disease resistance.

"Although we have identified lines with good levels of resistance to each of the four diseases, our challenge is to combine all four resistances in a single variety with high yield and good grade characteristics," he says.

Efforts to develop a variety with resistance to leaf spot have met with little success. NC 6 and NC 12C have some resistance, but Isleib notes that, when left untreated, both varieties will suffer as much as 70 percent defoliation before the end of the season.

More popular varieties VA-C 92R and VA 98R are extremely susceptible to leaf spot. Isleib's current breeding goals call for developing varieties with moderate levels of resistance that will allow growers to follow leaf spot advisory recommendations and eliminate one or more sprays per season.

When CBR first hit North Carolina peanuts in the 1960s, there was no commercially available chemical control. Breeders initiated a crash program to breed resistant peanuts. With the support of the North Carolina Peanut Growers Association, North Carolina Crop Improvement Association, and the North Carolina Foundation Seed Producers, the breeding program has released four CBR resistant varieties: NC 8C, NC 10C, NC 12C and Perry.

"Perry's release is the culmination of decades of selection for resistance," Isleib says.

"Today there are numerous CYB-resistant lines with good agronomic performance in our program, a testament to the work put into the project over the years by D. A. Emery, J. C. Wynne, M. K. Beute and the current project staff."

While it carries some resistance to CBR, NC 12C is highly susceptible to Sclerotinia blight, as is Gregory. Isleib says Sclerotinia blight has spread in North Carolina over the past few years as growers have planted more acreage of these susceptible varieties. Currently only VA 93B, VA 98R and Perry have partial resistance to Sclerotinia.

Breeders are now attempting to cross low yielding, but Sclerotinia resistant lines, with agronomically superior parents to produce high-yielding resistant lines. They are also attempting to transfer the resistance genes from Tamspan 90 Spanish peanut (the source of resistance in the runner-type variety Tamrun 98) into high yielding Virginia-type lines.

Through last season, Isleib characterized both NC-V 11 and Gregory as tolerant to tomato spotted wilt virus. However, he says the heavier than normal TSWV pressure this year may cause pathologists and breeders to revise their ratings before the 2001 planting season.

Isleib's variety performance tests on the Peanut Belt Research Station and in other locations around the state show how this disease has attacked all currently available peanut varieties. Until greater resistance is developed, specialists recommend planting one of the more tolerant varieties, and increasing seeding rates. In some incidences, use of a granular, in-furrow insecticide has also reduced TSWV incidence.

While much of Isleib's breeding work is concentrating on disease and insect resistance, he is also developing varieties which exhibit other desirable traits. Pod brightness, high-oleic oil content and improved flavor are three breeding targets.

He is also selecting lines of peanuts with oil content below 37 percent on a dry weight basis. These low oil peanuts would qualify to be marketed as reduced fat peanuts.

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