The effect of leaf area reduction on the yield and quality of sugar beet (Beta vulgaris L. var. altissima Döll).

The yield of sugar beet is directly affected by LAI (leaf area index) and values of LAD (leaf area duration). The integral leaf area plays, except for other factors, an important role during the damage or reduction of leaf apparatus. There are many sources of leaf damage: natural disasters (hailstorm), diseases, pests (including game browsing) etc. The intensity of the root production and quality differs in relation to the growth stage of the damage plant. The aim of this study was to evaluate the extent of losses in the root yield and the quality of sugar beet upon gradual reduction of the leaf area. Two diploid varieties Monza and Compact were used in the small-plot trials conducted in years 2004 to 2006 (in the experimental station Žabčice – maize production region, zone K2, average altitude 184 m, soil type was classified as gley fluvisoil, soil is medium heavy to heavy, clay-loam to loam type). The leaf area was manually reduced by 25% and 50% at BBCH 18–19 growth phase (8–9 leaves unfolded). The results were statistically evaluated by analysis of variance and testing by Tukey test (at the significance level α = 5%). Reduction of the leaf area was reflected on the decrease of the root yield by 1 to 10% depending on the year of harvest. In addition, the stressful state of the plants after defoliation resulted in the decrease of the yield of polarization sugar per hectare, namely by 0.45 to 1.66 t.ha–1. In 2005, the leaf area reduction caused a rise of the α-amino nitrogen content. The rise in the potassium and sodium cations content caused by the leaf area reduction also increased the sugar content in the treacle (by 0.1 to 0.16%). The increasing leaf area reduction lead to decreasing of yield of polarization sugar. However, this descent was statistically significant in harvest year 2006 only.