Description

In tests with wind-pollinated progenies from 540 parents, heritability of brown-spot resistance was 0.57, and that 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 breedings. In addition, individual seedlings less than 30% infected or more than 1 ft. tall were retained. Tests with iexposed 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% lessf brown-spot infection than those from parents with unknown history. Southwestern Alabama was the best of five geographic sources that were smapled for both height growth and brown-spot resistance.