Quantitative analyses of formation and reduction of yield elements in winter wheat cultivars Senta and Vlada (in 1988/1989 and 1989/1990), ST 146 line (1988/1989) and Vega cultivar (1989/1990) were performed at decisive growth stages under the following model conditions: stand density (seeding rates 2.5, 4.0, 5.5 million germinable seeds.ha-1); sowing date (first - September 20, second - October 5, third - October 20). As a basic method of statistical evaluation the analysis of variance of two-fold classification with replications was used. Differences between individual mean variant values were verified using the Tukey test. The study was aimed at assessing the characteristics of yield element formation, reduction and compensation in different winter wheat genotypes and increased utilization of yield potential by controlling yield elements. The data on characteristics of the genotypes studied are presented in Tabs I and II. The Senta genotype manifested intensive tillering; the tillers formed were considerably reduced. It was characterized by a high floret formation, a kernel number per spike and their weight. The Vlada genotype had a low tiller number; however, their high realization secured a high productivity of the stand density. It formed lower potential as well as actual spike productivity. The Vega genotype showed a lower intensity of tiller production, however, with a high percentage of their realization. It produced a high floret number per spike which was considerably reduced. It reached a high kernel weight. The ST 146 line established high numbers of tillers and productive stems. It considerably reduced the florets formed and showed a low spike productivity. Yield element formation was significantly controlled by stand density (Tabs III, IV). At the raising seeding rate a number of tillers and productive stems per plant reduced; however, the productive density of the stand did not significantly differ at the seeding rates investigated (it was compensated by a plant number). The seeding rate was in negative correlation with both the number of formed florets and actual kernels per spike. A higher kernel number per spike at the seeding rate of 2.5 million germinable seeds.ha-1 significantly increased the spike productivity and stand sink, which positively affected the grain yield. Spike weight was not significantly influenced. Tillering dynamics, floret formation and reduction was influenced by sowing dates (Tabs V, VI). A later sowing date significantly reduced a tiller number established both per spike and 1 m2. Their unevenness increased (Tab. VII). The first sowing date secured a higher number of productive stems per unit area as compared to both later ones. Plant development at various sowing dates was delayed and therefore, floret formation and reduction always took place in different periods and were influenced by weather conditions. At a later sowing date, a kernel number per spike as well as stand sink fell down. This reduction was not compensated by an increased kernel weight and grain yield decrease was noticed. Based on the results obtained the following conclusions can be drawn. Considering the grain yield formation early growth stages were very important during ontogenesis; they affected a tiller (spike) number and significantly expressed in subsequent formation of a final kernal number which expresses accumulation capacity. Early and balanced tillering is desirable. This requirement is dependent on the influence of weather conditions during the year. In winter wheat, it can be limited by an early sowing date. The seeding rate of 2.5 million seeds.ha-1 optimized the ratio between yield elements and positively affected grain yield. The results showed that from the point of view of breeding for production ability the genotypes not only with high production potential but as well as with its high realization are suitable.
