Changes in Sugar Content in Winter Wheat during Overwintering

A three-year field study (2005-2007) of winter wheat was conducted on lessive brown soil, silt loam at the Study and research farm "Peterlauki". The study covered three genetically different winter wheat cultivars (‘Cubus’, ‘Tarso’, and ‘Zentos’). Wheat was sown on 4 different dates with a 10-day interval in the period from the end of August until the end of September by using three sowing rates (300, 400, and 500 fertile seeds per 1 m²) in four replications. Samples for identification of sugar content were taken from all cultivars in autumn at the end of vegetation period and in spring at the beginning of vegetation by cutting the surface part of the plant. During overwintering - end of January and beginning of February - samples were taken from all wheat varieties sown on all sowing times with the sowing rate of 400 fertile seeds per 1 m². The study revealed that sugar content in autumn, prior to the end of vegetation, was the highest for early sown winter wheat, but slightly decreased with each succeeding date of sowing. However, prior to overwintering, differences in sugar content among plants sown on different dates depended on the length of autumn season and on fluctuations in temperature during that period. Sugar content was different among different varieties, and changes that were identified during the vegetation period depended mainly on wintering conditions. If varieties with rich tillering and intensive growth in autumn were sown early, they lost greater amounts of sugar during overwintering. Although sugar content in plants in spring differed considerably year after year, differences in sugar content among the plants sown on different dates within one year almost completely leveled out and were slight. Plants rich in above-ground biomass utilised considerably more sugars to support their life function in the period of wintering. In the spring with comparatively early beginning of vegetation, relatively more sugar had remained in plants out of the amounts accumulated in autumn period in comparison to the spring with late beginning of vegetation. No impact of the sowing rate on sugar content and its changes during the vegetation period was identified