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Photoassimilate Partitioning of Main Shoot Leaves in Field-Grown Spring Barley¹

Premature tiller mortality could conceivably limit grain yield production in barley (Hordeum vulgare L.). Knowing photoassimilate partitioning patterns during the vegetative development phase of growth is important for understanding the causes of tiller mortality. A field experiment was conducted to ascertain the ¹⁴C translocation patterns of individual main shoot leaf blades during the pre-anthesis period for three spring barley genotypes differing in tiller production and survival. One of the top three to five leaves was labelled with ¹⁴CO₂ on each date and above-ground plant parts were harvested for determining the distribution of ¹⁴C after a 24 h translocation period. Also, for two of the leaves, labelled plants were allowed to translocate until anthesis or maturity before the distribution of radioactivity was measured. Most ¹⁴C fixed by the first developed leaves on the main shoot was translocated to newly emerging main shoot leaves or to young tillers. The leaf subtending and the leaf above a particular tiller preferentially exported carbon to that tiller. During the early tiller production phase of growth, proportionately more ¹⁴C was translocated to tillers of the higher tillering genotypes than for the lower tillering one. During the time when tiller mortality became evident, no differences in partitioning patterns were found between the high or low tiller mortality genotypes. Later formed leaves in all genotypes provided relatively large proportions of labelled photoassimilate to the main shoot stem and inflorescence. A sharp decline in the percentage of ¹⁴C translocated to all tillers occurred when the main stem began rapid growth. We conclude that the shift in main shoot photoassimilate translocation away from tillers and to the main shoot stem contributes to the premature abortion of tillers in barley.

Key Words: Tillering • Translocation • Hordeum vulgare L.

² Graduate research assistant and associate professor, Univ. of Minnesota, St. Paul, MN 55108.

Received for publication September 14, 1984.