High digestible dry matter yield is desired by maize (Zea mays L.) silage producers. The brown midrlb‐3 mutant (bm3) improves the digestibility of maize stover but reduces grain and fodder yields of homozygous bm3 genotypes. Our objective was to estimate the relative genetic potential for improvement of silage quality and yield in bm3 and normal maize populations. A total of 130 bm3 and normal 130 S1 lines were developed from three populations segregating for the bm3 allele. All 260 S1 lines were evaluated at two Minnesota locations in 1978. In 1979, 64 bm3 64 normal S1 lines, and 24 bm3 and 24 normal S1 ✕ S1 hybrids were evaluated at three locations.The bm3 genotypes averaged 77% of the grain yield, 90% of the stover yield and 84% of the fodder yield of the normal genotypes. Some bm3 genotypes produced as much stover as the best normal genotypes. However, no bm3 genotypes produced as much grain or fodder as the best normal genotypes. The normal genotypes yielded 16% more digestible dry matter than the bm3 genotypes. Estimates of genetic variability and predicted genetic gain for digestible dry matter yield were similar for bm3 and normal populations. Even though bm3 germplasm offers a substantial advantage in stover digestibility, our results indicate normal populations of maize may offer more potential for silage breeding programs.

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The brown midrib‐3 mutant (bm3) improves the ruminant digestibility of maize (Zea mays L.) sotver, but homozygous bm3 plants are usually less vigorous than normal plants. Because early season vigor can influence final grain and stover yield, our objective was to investigate the potential for genetically improving the early vigor of bm3 genotypes relative to normal genotypes. A total of 130 bm3 and 130 normal S1 lines were developed from three populations segregating for the bm3 allele and were evaluated in three field environments in Minnesota. Average seedling dry weight of the normal lines was 10% higher than the bm3 lines, but a few bm3 lines had seedling dry weights as high as the best normal lines. Predicted gains from selection among bm3 lines were similar to normal lines of the same population. Dry matter accumulation rates of the normal lines during vegetative growth averaged 13% higher than the bm3 lines, but a few bm3 lines had rates as high as the best normal lines. Two bm3 and two normal S1 lines and their hybrids within bm3 and normal genotypes were evaluated for dry matter accumulation rate over the entire growing season. The average linear accumulation rate of total dry matter was 15% higher in the normal genotypes. The lower rate of grain filling of the bm3 genotypes was somewhat compensated for by a longer effective duration of grain filling. Our results suggest that bm3 populations could be improved to acceptable levels of early vigor and growth rate.

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