Diseases are major yield limiting factors in peanuts in the USA and around the world. The University of Florida peanut breeding program has put considerable emphasis on breeding for pest resistance, especially to late leaf spot, stem rot/white mold (S. rolfsii), and tomato spotted wilt virus (TSWV). ‘Southern Runner’ was the first cultivar released (1986) from this program that had documented multiple pest resistance. Southern Runner, numerous breeding lines and plant introductions have since been used in the Florida program to provide growers with ever better cultivars with improved pest resistance. Recently ‘Florida MDR 98' was released with essentially the same “resistance package” as Southern Runner, but with improved levels of disease resistance and better agronomic characteristics.

The MDR in Florida MDR 98 stands for Multiple Disease Resistance. MDR 98 originates from a cross made in 1984 between Southern Runner and an F1 plant from Andru 93 and UF81206. UF81206 has better disease resistance to leaf spot, white mold, and rust than Southern Runner with some resistance to root knot nematode, but typically grades poorly. We wanted to get some earliness and seedling vigor from Andru 93 from this cross. A pedigree selection program was followed in the F2 - F4 generation under unsprayed conditions (no leaf spot control). Seed from F5 plants were bulked to initiate yield tests. Florida MDR 98 was tested as 84x28-5-4- 2-b3-B or UF91108. UF91108 or Florida MDR 98 was first yield tested in 1990 under unsprayed conditions at Marianna, Florida and was entered in sprayed tests in Marianna and Gainesville in 1991. UF91108 was tested in the Uniform Peanut Performance Tests (UPPT) in all major peanut producing states in 1993-95.

Florida MDR 98 has shown moderate to good resistance to late leaf spot, white mold, TSWV, and rust, with greater pod yields, larger seed size, and better grades than Southern Runner. MDR 98 also has mid-oleic (65% oleic fatty acid) oil chemistry, as compared to about 50% for Florunner and 80% for SunOleic 97R.

Table 1 gives data from unsprayed (no leaf spot fungicide) yield tests conducted at Marianna from 1990-96. In the unsprayed (leaf spot) yield tests at Marianna (1990-96), MDR 98 showed a 16% yield advantage over Southern Runner, with total sound mature kernels (TSMK) value of 81.3% for MDR 98 vs. 79.1 % for Southern Runner. These results clearly show the leaf spot resistance of MDR 98 is superior to that of Southern Runner. The data in Table 2 are from Marianna tests that were sprayed full season for leaf spot control. Six tests had MDR 98 and Florunner and three tests in 1993-95 had MDR 98, Florunner, and Southern Runner. MDR 98 had a 33% yield advantage over Florunner in the 1991-96 tests and a 6.9% yield advantage over Southern Runner in the 1993-95 tests at Marianna. MDR 98 also had lower disease ratings and better grades.

Table 3 gives data from tests conducted in Gainesville from 1991-95. These data further support the results from the Marianna studies, indicating a yield and grade advantage for Florida MDR 98 over Florunner and Southern Runner.

The pod yield and grading data in Table 4 are from the 1993-95 Uniform Peanut Performance Tests at Marianna, Headland (Alabama), and Tifton (Georgia). Florida MDR 98 had a 26.7% yield advantage over Florunner in these tests, with better grades.

Results from Marianna field studies that were inoculated with S. rolfsii, which causes stem rot/white mold, are presented in Table 5. Florida MDR 98 had a 43.6% pod yield advantage over Southern Runner and a 224% yield advantage over the highly susceptible Florunner. This indicates that MDR 98 has even better resistance to white mold than Southern Runner.

Table 6 gives results from early planted studies conducted at Marianna and Attapulgus, Georgia, to evaluate for tomato spotted wilt virus (TSWV). These tests were planted in early April and at low seeding rates (1.5 seed per row foot) to enhance development of TSWV. Florida MDR 98 gave a modest yield advantage over the resistant Southern Runner with a significant yield advantage over the susceptible Florunner, with lower disease incidence and severity.

Table 7 gives results from a 1997 April-planted variety test at Marianna that had extremely severe TSWV pressure. Florida MDR 98 had significantly greater pod yield than Georgia Green (nearly 1000 lbs/A), which was the second highest yielding runner type variety in the test. MDR 98 also had the lowest disease level and best grades (79.2% TSMK).

All of the data clearly supports the multiple disease resistance of Florida MDR 98. The resistance to late leaf spot, white mold, and TSWV should help reduce risk to growers from potential loss from these disease problems. MDR 98 does not have immunity to these diseases but is more resistant than any peanut cultivar currently available. A grower should be able to reduce leaf spot and white mold control costs with MDR 98, similar to that obtained with Southern Runner. However, MDR 98 does have the same late maturity as Southern Runner and possibly similar seedling vigor. Further management studies are being conducted on the best ways to cut fungicide cost.

Seed supply will be limited for the 1998 crop and probably continue to be limited in 1999. Hopefully, a good supply of seed will be available in the year 2000.

For more information on any of these or related topics, feel free to contact Albert Culbreath by phone (912) 386-3370, fax (912) 386-7285 or email (spotwilt@tifton.cpes.peachnet.edu).