FORMATION AND REDUCTION OF YIELD ELEMENTS IN WINTER-WHEAT

Quantitative analyses of formation and reduction of yield elements in winter wheat cultivars Senta and Vlada (in 1988/1989 and 1989/1990), S T 146 line (1988/1989) and Vega cultivar (1989/1990) were performed at decisive growth stages under the following model conditions: stand de nsity (seeding rates 2.5, 4.0, 5.5 million germinable seeds.ha-1); sow ing date (first - September 20, second - October 5, third - October 20 ). As a basic method of statistical evaluation the analysis of varianc e of two-fold classification with replications was used. Differences b etween individual mean variant values were verified using the Tukey te st. The study was aimed at assessing the characteristics of yield elem ent formation, reduction and compensation in different winter wheat ge notypes and increased utilization of yield potential by controlling yi eld elements. The data on characteristics of the genotypes studied are presented in Tabs I and II. The Senta genotype manifested intensive t illering; the tillers formed were considerably reduced. It was charact erized by a high floret formation, a kernel number per spike and their weight. The Vlada genotype had a low tiller number; however, their hi gh realization secured a high productivity of the stand density. It fo rmed lower potential as well as actual spike productivity. The Vega ge notype 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 we ight. The ST 146 line established high numbers of tillers and producti ve stems. It considerably reduced the florets formed and showed a low spike productivity. Yield element formation was significantly controll ed by stand density (Tabs III, IV). At the raising seeding rate a numb er of tillers and productive stems per plant reduced; however, the pro ductive density of the stand did not significantly differ at the seedi ng rates investigated (it was compensated by a plant number). The seed ing rate was in negative correlation with both the number of formed fl orets and actual kernels per spike. A higher kernel number per spike a t the seeding rate of 2.5 million germinable seeds.ha-1 significantly increased the spike productivity and stand sink, which positively affe cted the grain yield. Spike weight was not significantly influenced. T illering dynamics, floret formation and reduction was influenced by so wing dates (Tabs V, VI). A later sowing date significantly reduced a t iller number established both per spike and 1 m2. Their unevenness inc reased (Tab. VII). The first sowing date secured a higher number of pr oductive stems per unit area as compared to both later ones. Plant dev elopment at various sowing dates was delayed and therefore, floret for mation and reduction always took place in different periods and were i nfluenced by weather conditions. At a later sowing date, a kernel numb er per spike as well as stand sink fell down. This reduction was not c ompensated by an increased kernel weight and grain yield decrease was noticed. Based on the results obtained the following conclusions can b e drawn. Considering the grain yield formation early growth stages wer e very important during ontogenesis; they affected a tiller (spike) nu mber and significantly expressed in subsequent formation of a final ke rnal 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 lim ited 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 breedin g for production ability the genotypes not only with high production p otential but as well as with its high realization are suitable.