The revealing and selection of high-protein sources of maize
--V.E. Micu, Eugenia Partas and A.I. Rotari

This research began in 1974. In the first stage (1974-80) the protein content of 1,572 populations and samples was determined by the Kjeldahl semi-micromethod. In the investigated collection, including large diversity in geographical and genetic origin, morphology, growing period and other traits, samples with high protein content (12-15%) were revealed, the majority of them among local flint populations from Moldova.

In the second stage, the individual selection of high-protein plants in the best population was conducted and the results for four of them (K-44, K-466, K-553, K-1081) are presented in Table 1. Annually, 10-20 plants were self-pollinated and analyzed for protein content. Though the volume is limited, nevertheless each of the four populations reveals large genetic diversity among plants in protein content. Using long-term selection, progenies with protein content of more than 23-24% have resulted, significantly exceeding the initial level. It is necessary to note that the best progenies, with 23-24% protein, were obtained in population K-466, which had the highest initial protein content (Table 1) and highest variation. After 12 years of selection, genetic variability of protein content is not settled, as shown by the 1992 data.

Table 1. The protein content in self-pollinated progenies of the last 10 cycles of selection (% in dry matter).
 

Cycles of Selection & Year	K-44 lim	K-466 lim	K-553 lim	K1081 lim
Initial Level	12.12-12.75	13.25-15.69	12.25-13.75	14.44-14.91
3 - 1983	17.08-20.09	15.88-20.69	13.72-18.41	15.64-19.25
4 - 1984	17.06-19.00	14.68-23.35	16.37-19.25	15.88-21.66
5 - 1985	15.52-19.37	15.16-19.85	17.44-19.61	12.51-15.88
6 - 1986	13.96-19.12	12.27-21.30	15.88-16.60	12.27-16.00
7 - 1987	15.06-19.61	14.19-22.65	17.69-18.08	15.64-17.69
8 - 1988	16.97-21.17	14.80-20.21	17.08-19.13	13.83-18.53
9 - 1989	17.20-21.39	15.61-24.27	17.31-20.45	16.36-18.78
10- 1990	18.24-20.02	17.88-23.86	18.81-19.27	17.05-19.50
11- 1991	18.79-21.02	18.03-23.71	17.15-20.18	15.40-18.26
12- 1992	16.03-17.71	17.37-21.53	15.67-17.88	16.60-17.05
Populations limit	12.12-21.39	12.27-24.27	12.25-20.45	12.27-21.66
No. of Analyzed Progenies	159	626	60	68

The third stage of work began in 1987 and includes the cross of the four families highest in protein, self-pollination of hybrids, and selection in segregating progenies. Protein content in 1989-93 was determined by Near-Infrared method mod. 4500. In the F1 in all cases the protein content decreased considerably (Table 2), but the best progenies of the F2-F5 generation exceeded the best of the parental component by a considerable extent, except the hybrids with K-466. In these, the protein content of cross progenies was 21.05%, and the best selections from the F2-F5 had lower protein contents.

Nevertheless, even with these exceptions, the results testify to: (1) the presence of various genetic factors in different high protein sources; (2) the possibility of concentration of genetic factors favorably affecting the protein content from different sources into one. This allows us to expand the genetic base for further selection of a high-protein source. The work will be continued in this direction in order to obtain a source of high protein unrelated to IHP.

Table 2. The protein content of crossed families (1987), their best progenies (1988-92) and their F1-F5 (% in dry matter).
 

Sources & Hybrids	1987	1988	1989	1990	1991	1992
K-44 female	17.93	19.45	19.05	19.10	19.95	17.75
K-1081 male	16.40	16.26	17.60	18.40	17.35	17.48
K-44 x K-1081		15.83	21.30	23.31	23.40	21.95
K-1081 female	16.10	16.40	16.21	17.60	18.40	17.3
K-553 male	16.00	17.93	18.30	18.20	18.55	18.90
K-1081 x K-553		14.49	16.60	19.55	20.40	21.10
K-1081 female	15.04	16.38	16.10	17.58	18.35	17.35
K-466 male	21.05	18.03	18.14	20.40	20.87	20.48
K-1081 x K-466		15.52	19.85	18.90	21.45	20.58

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