Agronomic Traits and Nutritive Value of Stover in Brown Midrib-3 Maize Hybrids

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  • Brown midrib-3 トウモロコシ交雑種の栽培特性及び茎葉部の成分と消化性
  • Brown midrib-3 トウモロコシ コウザツシュ ノ サイバイ トクセ

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Field trial and in situ digestion trials with brown midrib-3 maize hybrids were carried out to determine the effect of brown midrib-3 (bm_3) gene on agronomic traits and nutritive value of stover in Chushin dist., Nagano, Central Japan. In 1987, comparisons were made between isogenic materials, normal (1/2 of plants) and bm_3 (1/2 of plants) from two triple hybrids developed with inbred lines. The seed parents were yellow dent hybrids (S_4 lines homozygous for the normal allele × S_6 line homozygous for the bm_3 allele) derived from an American hybrid and an American synthetic variety. The pollen parent was a white flint inbredline (S_1 line homozygous for the bm_3 allele) derived from a Yugoslavian local variety. The bm_3 (homozygous for the bm_3 allele) and normal (heterozygous) stands were grown at the rate of 625 plants/a in a split-plot design with two replicates by thinning after appearance of brown pigment on the midrib. Vigor in early growth and maturity were similar in both phenotypes : bm_3 type (homozygote for bm_3) and the normal type (heterozygote). The effect of heterozygosis for bm_3 on stalk length, ear height, lodging resistance at silage harvest appeared to vary according to the genetic background of seed parents. Dry matter yields of bm_3 type were 10-20% lower than the normal type. In comparison with the nomal type, the number of ear per unit area in brn3 type decreased but the proportion of grain in whole-crop dry matter of bm_3 type were not decreased. Whole-crop dry matter concentration and the proportions of organic cellular content, organic cell wall content (OCW), NDF, ADF and silica in stover did not differ significantly. In comparison with the content of low digestible fraction in OCW (Ob) and the ADL concentration in stover for bm_3 homozygote were 6% and 2% lower, and the in vitro digestibility of OCW and content of estimated digestible organic matter were 10% and 4% higher on the averages, respectively. 24-hr in situ disappearance of dry matter in whole-crop harvested at silking stage was also 4% higher for homozygote than for heterozygote when used steers. It is concluded that the gain of digestible organic matter content in stover and whole crop of bm_3 hybrids through heightened cell wall digestibility is about 4%, but the dry matter yield loses 15-20%. These results indicate that the combining ability and dry matter productivity of parental lines are important for breeding bm_3 hybrids.

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