The effect of growth regulators on the yield and quality of sugar beet roots

Growth regulators (biologically active substances) in sugar beet are used t o improve biological values of seed and growth regulation and development o f the course of vegetation with an aim to increase the yield of roots and t heir sugar content. The possibilities of effect of intensive formation of n ew leaves in spring period or deposition of reserve substances into root in autumn, increase of sugar content and sugar production per 1 ha were inves tigated. Regulation of the process of formation of white sugar yield is ver y complicated. In view of hormonal regulation Kutina (1988) and Prochazka e t al. (1997) tried to characterize it briefly. Zahradnicek et al. (1996) re ports that in despite of majority of other plant materials in which cytokin ins of zeatin type prevail, cytokinin N-6-(delta(2)-isopentenyl)adenin was dominant. The degree of reaction of selected sugar beet variety thigh sugar content Edda and normal Hilma) on application of growth regulators was stu died. In exact small-plot field trials in the experimental station at Uhrin eves the effect of growth regulators on amount and quality of harvested sug ar beet roots was evaluated. Applications of growth regulators Rastim 30 DK V (0.3 l.ha(-1), active substance benzolinon), Atonik (0.6 l.ha(-1), aromat ic nitrocompounds) and highly effective Cytokinin R [3.10(-6) M, (meta-hydr oxy benzyl)adenosine] tin special literature denoted as mOH.BAR) were inves tigated. The first spraying was applied in growth stage 31 to 33 (6 to 14 l eaves). The second one about six weeks before harvest, in the growth stage 42 to 46. Fertilization and agrotechnics of the trial were usual. Soils of experimental station at Uhrineves are deep, they belong to great soil group Luvisol. Average daily air temperature is 8.3 degrees C, during the growin g season 14.6 degrees C. Average yearly precipitation amounts to 575 mm, ou t of this period April to September 380 mm. The results of three-year trial s (Tabs I and II) confirm a positive effect of selected growth regulators o n the amount of harvested sugar beet roots. Significant increase of root yi eld on average of studied years was found in autumn treatment with cytokini n, Atonik as well as Rastim 30 DKV in both the studied varieties but it was more marked in more yielding variety Hilma. The highest increase against u ntreated control on average of studied years was recorded after two treatme nts of the stand with Rastim 30 DKV (13.7% increase). Rastim 30 DKV acted m ost significantly in the variety Hilma in different years. The effect of st udied substances on sugar content was very low in all three experimental ye ars. Our previous opinion that application of growth regulators may rather affect amount of production than its quality given by sugar content above a ll. This applies to varieties with genetically conditioned higher sugar con tent (C and NC types). Increased root yield after stand treatment with inve stigated growth regulators reflected in the increase of sugar production, m ore significantly in the variety Hilma than Edda. On average of investigate d years the yield of white sugar against untreated control increased in the variety Edda as much as by 7.1% in the variant treated with cytokinin four to six weeks before harvest. In the other studied variants an increase var ied from 1.6 to 3% on average. In the variety Hilma increase was more marke d particularly in variants with pre-harvest-autumn application (by 11 to 15 %). Conclusions (Pulkrabek, 1995) that double treatment with Atonik or Rastim 3 0 DKV increase root yields per 1 ha by 3 to 5% and that it does not affect significantly the sugar content of sugar beet yield should be added by the fact that in yielding and normal varieties (e.g. Hilma) increase of the roo t yield is higher than in varieties with high sugar content (e.g. Edda). It follows from the previous trials (Zahradnicek et al., 1996) evaluating the effect of leaf application of Atonik that root losses during storage befor e their technological processing are lower than in untreated control. These conclusions were also confirmed in the laboratory tests (Kotyk ct al., 199 6). They manifest decreased rate of respiration after treatment of sugar be et with Atonik. In summary the effect of leaf treatment of sugar beet with Atonik can be evaluated very positively. It increases sugar production in t he field and it decreases storage losses of sugar before its technological processing by lower respiration during storage.