Research on selected high quality protein hybrids
--Z. X. Liu, S. F. Jia, Q. F. Guo, J. F. Xu and L. M. Wang

Better normal maize inbred lines were crossed with o2 (floury endosperm) inbred lines, by means of inbreeding, backcross and many other methods, to develop new and excellent agronomic characteristics in o2 inbred lines. In order to overcome such defects of o2 lines as lower grain yield and floury endosperm, the lines selected were crossed with high quality protein maize populations, which carry the o2 gene with modified endosperm texture. After several generations of inbreeding and selection of hard endosperm, we obtained maize inbred lines with high quality protein and modified endosperm texture, which make them indistinguishable from other normal flint lines.

The best lines obtained have an average lysine content of from 0.35% to 0.42% in whole kernels, which is an increase of 75% to 110% over normal lines. The protein content is from 8.7% to 11.2% and similar to normal lines. For example, the protein content of QI205 is 10.2% and its lysine content is 0.4% in whole kernels. It has outstanding agronomic characteristics and has been used in the production of hybrids.

We bred high quality protein maize hybrids with not only higher lysine content, but also higher grain yield. For instance, LUDAN203 was crossed by two excellent o2 lines (ZHONGXI091 and QI205). The hybrid has a higher grain yield of 8,500 kg/ha in general, and the maximum grain yield will reach more than 12,750 kg/ha. In 1990 and 1991, average grain yields of LUDAN203 were 8,325 and 8,355 kg/ha respectively in the state regional test across 18 experimental sites, with increases of 21.8% and 18.5% over normal maize hybrid ZHONGDAN2 (6,833 and 7,065 kg/ha) as check. The normal maize hybrid once obtained the highest invention prize of our country. Protein and lysine content in whole kernels of LUDAN203 are 9.8% and 0.40%. It also has excellent agronomic characteristics and has received wide utilization. Recently, the planted area of this variety has reached more than 6,000 hectares.

A significant feeding effect of the hybrid was obtained when LUDAN203 was used as feed for hens and pigs in 1991. The daily increase of gross weight and the rate of egg production of test hens rose by 20% and 26.8% respectively over normal maize check hybrid (YEDAN4). The daily increase of gross weight of test pigs rose by 35% over the normal maize check hybrid.

The results obtained indicate that in the o2 genetic background it is effective to select high quality protein maize hybrids with modified endosperm texture (hard endosperm) so as to obtain higher grain yield. The effectiveness is higher in flint maize than in dent maize due to the fact that in the former it is easier to develop the modified endosperm texture kernel than in the latter.

Nevertheless, we believe the characteristic of multiple rows of the ear is important to increase kernel number, and to obtain higher grain yield in the selection process. For example, LUDAN203 has more than 800 kernels per ear. This is an easy way for the intercession of the negative correlation between high quality and high grain yield.

In addition, the lysine content in kernels has been taken into account in selecting lines of the high quality protein and modified endosperm texture. As a matter of fact, there is still room for improvement in our work. We hope to develop high-yielding hybrids with high quality protein and hard endosperm in the near future. 

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