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Breeding Longleaf Pines for Resistance to Brown Spot Needle Blight. E. Bayne Snyder, Principal Plant Geneticist, Institute of Forest Genetics, Gulfport, Mississippi 39501, Southern Forest Experiment Station, USDA Forest Service; Harold J. Derr, Principal Silviculturist, Alexandria Forestry Center, Pineville, Louisiana 71360, Southern Forest Experiment Station, USDA Forest Service. Phytopathology 62:325-329. Accepted for publication 7 October 1971. DOI: 10.1094/Phyto-62-325.

In tests with wind-pollinated progenies from 540 parents, heritability of brown-spot resistance was 0.57, and that of height was 0.52, at age 3 years. Infection in progeny of the best 10% of parents averaged 48%, compared to a population average of 63%. This 10%, plus the fastest growing seedlings, were selected for second-generation breeding. In addition, individual seedlings less than 30% infected or more than 1 ft tall were retained. Tests with exposed and protected progeny indicate that inherent fast height growth is not the major mechanism of resistance. The frequency of brown-spot resistant genotypes varied by seed source, especially where there were differences in parental exposure to the disease. Offspring from parents selected 30 years earlier from a heavily infected planting averaged 55% taller and had about 10% less brown-spot infection than those from parents with unknown history. Southwestern Alabama was the best of five geographic sources that were sampled for both height growth and brown-spot resistance.