Combining ability of the total grain nitrogen, yield of nitrogen and grain yield in two sets of diallel crosses was studied. In the first set high protein inbred lines Early 7, Tva200HP, Hymador 222, P270 Barilles and P263-213, were used. In the second set of diallel crosses, except for the above-mentioned inbreds, normal inbreds Tva10870 and F115 were included. The combining ability was analyzed according to Griffing (Model I, Method I). The results are as follows:
1. Analysis of genetic variability of the content of the total grain nitrogen showed significant influence of GCA on this character in both diallel sets.
2. GCA:SCA ratio (1:2) in the first diallel set indicates that grain yield in high protein inbreds is mainly determined by SCA. By including normal inbreds in the diallel set the ratio of GCA:SCA becomes more nearly equal (1:1). Comparison of this finding with our previous unpublished studies, in which combining ability of yield of normal inbreds was determined only by GCA, shows that grain yield of normal and high protein genotypes is probably controlled by different genetic systems. This conclusion is in agreement with the assumption of Pollmer et al. (Z. Pflanzenz. 80:142-147), that decreased yield potential of high protein genotypes is a consequence of long-term selection pressure, during which the genetic system controlling grain yield has changed.
3. Reciprocal differences in the content of the total grain nitrogen were found only in the F1 generation. No reciprocal effects were found in further generations. This fact confirms our previous finding from breeding of high protein inbreds, that any differences in the protein content between direct and reciprocal crossing disappeared after three generations of self-pollination. This conclusion could be used in breeding of high protein genotypes to eliminate some negative characters of the genetic source.
4. As for the yield of nitrogen, it is more dependent on grain yield than on nitrogen content. Correlation coefficient between yield of nitrogen and grain yield was 0.885**. No correlation was found between grain yield and content of the total grain nitrogen.
5. The best hybrid combination from the diallel sets was Hymador 222 x F115, which had nitrogen content of 15.25% and reached a grain yield of 8.60 t.ha-1 and a nitrogen yield of 1.31 t.ha-1. There were other hybrid combinations of the high protein x normal type, which overcame the population mean in all characters. This shows a possibility of production of high protein hybrids with good yield potential by combination of the high protein x normal genotypes.
H. Zeleke, A. Piovarci, M. Nesticky
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