Oat Stem Vascular Size in Relation to Kernel Number and Weight. I. Controlled Environment

The increase in dry weight of seeds in cereals is dependent on the transport of carbon. There is however little information regarding the capacity of the vascular system of oats to transport carbohydrates to the panicle. To describe the capacity of the vascular system of the upper stem internode of nearly mature oats (Avena sativa L.),we measured the number and size of vascular bundles, phloem area, and number of sieve tube members in cross sections of two cultivars (‘Goodland’ and ‘Froker’) grown in a controlled environment. Cultivar differences were examined, and measurements were related to kernel number and yield/panicle. Also, measurements were made on cross sections of each internode of the panicle main axis of Froker. The stem diameter, vascular bundle number and area, and the number of sieve tube members were significantly greater in Froker than in Goodland. Froker also had significantly more kernels and higher yield/panicle than did Goodland. Stem diameter, bundle number, bundle area, and phloem area were good predictors (as determined by regression analysis) of the number of kernels/panicle (r² = 0.80, 0.66, 0.77, and 0.61, respectively) and of yield/panicle (r² = 0.75, 0.55, 0.74, and 0.61, respectively). Mean values associated with the vascular measurements declined from the lower to the upper internodes of the panicle main axis of Froker, but did so less rapidly than did the number of spikelets or kernels produced on branches from the corresponding nodes. Thus, kernels developing on upper panicle node branches were served by more vascular tissue/kernel than were those of the lower nodes. The results of this study suggest that the capacity of the vascular system to transport carbohydrates may be associated with differences in kernel size within panicles and with spikelet blasting.