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Photosynthate Partitioning in Sugarbeet¹

Partitioning of photosynthate to various parts of a crop has a marked influence on economic yield. We used the sugarbeet (Beta vulgaris L.) to investigate quantitatively the effect of this partitioning on growth. Plants were grown for 21 days in the growth chamber. Partitioning was measured indirectly by using the Taproot- Leaf Weight Ratio (TLWR), where TLWR = Taproot fresh weight + Leaf lamina fresh weight. Our objectives were to study the pattern of variability of TLWR within and among sugarbeet breeding lines and hybrids, the effect of selection on TLWR, and the detectability of differences in TLWR at various stages of vegetative development.

In selection studies, seedlings with the lowest and highest TLWR 21 days from emergence were selected for polycross seed production. Progenies of two cycles of selection were tested. Ontogeny of TLWR was followed for 21 days from emergence.

Populations differed significantly in mean TLWR. Within unselected populations, TLWR of individual seedlings varied more than twofold among some of the 24 breeding lines and hybrids examined. In the first cycle of selection in line EL 40, mean TLWR of the high- TLWR parents was 83% greater than that of the low, and progenies from the high TWLR selections differed from the low by 38%. In the second cycle, the parents differed by 118% and the progenies by 60%. The responses observed in the two cycles of selection indicate that TLWR is genetically controlled.

During the 21 days from emergence, the TLWR was high at 3 days, the first measurement, decreased more than fivefold to a minimum near 15 days, and then increased gradually thereafter. TLWR is not correlated with taproot weight and only slightly correlated with leaf lamina weight at 21 days.

Key Words: Taproot • Fibrous roots • Beta vulgaris L. • Allocation • Translocation • Assimilate • Selection

² Plant physiologists, Light and Plant Growth Laboratory, Plant Physiology Inst., FR-SEA, USDA, Beltsville, MD 20705.

Received for publication September 26, 1977.

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