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Compensatory Response of Sunflower to Stand Reduction Applied at Different Plant Growth Stages¹

Differential plant populations occurring among plots in yield trials can be critical in evaluating potential worth of sunflower (Helianthus annuus L.) hybrids or breeding lines. The objective of this study was to determine degree of loss in seed yield when stand is reduced at various growth stages of plant development and to identify the nature of plant compensation for stand loss in sunflower.

No significant reductions in seed yield occurred when plant populations were reduced 25% from the check (50,000 plants/ha) at the 4, 8, and 16-leaf growth stages. Compensation was due to significant increases in head diameter. Stand loss of 25% at later growth stages resulted in significant yield loss. Compensation occurred in seed weight as well as head diameter when stands were reduced 50% at early growth stages. Seed yields were reduced 18 to 23%.

Sunflower plants were able to significantly compensate even when 75% stand reduction was applied at bud and flowering stages, with seed weight accounting for most recovery in yield. A 38 to 42% and 56 to 58% loss occurred when stands were reduced 75% at the 4 to 16-leaf and bud to flowering growth stages, respectively. Oil percentages of seeds from plants grown in plots with high stand reductions were reduced 6% and height was decreased 25 cm. Significant negative correlations were noted between oil percentage and height with yield, head diameter, and seed weight at the lowest plant population. Plant population would be critical to control in studies investigating inheritance of plant height or oil percentage of sunflower.

Key Words: Helianthus annuus L. • Seed yield • Sunflower breeding • Plant population • Stand reduction

² Research geneticists, USDA, ARS, Dep. of Agronomy, North Dakota State Univ., Fargo, ND 58105.

Received for publication January 16, 1981.