Effect of the Brown Midrib‐3 Allele on Early Vigor and Growth Rate of Maize1

Abstract

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.