INTERHYBRID COMPETITION AFFECTS SUNFLOWER CHARACTER EXPRESSION

Field researchers are confronted with selection of the proper plot des ign to assure agreement of small-scale experimental plot results with large-scale commercial field production. The objective of this researc h was to investigate the effect of plot design on expression of hybrid sunflower (Helianthus annuus L.) characters. Field studies were condu cted in North Dakota at three dryland sites: Carrington, Fargo, and Pr osper. Interhybrid and intrahybrid competitive situations were attaine d by using one-row or two-row hybrid arrangements with three hybrids a s possible borders. Competitive effects were determined on achene yiel d, achene oil concentration, achene weight, test weight, days to anthe sis, head diameter, plant height, and leaf number. Plot achene yield w as 20% greater when the border hybrid was a semidwarf than when border hybrids were of more conventional height. Border hybrid competitive i nfluences on achene yield were approximately twice as great for one-ro w as for two-row arrangements. Other characters influenced by interhyb rid competition were test weight, head diameter, and plant height. Cha racters not influenced by interhybrid competition included achene weig ht, achene oil concentration, days to anthesis, and leaf number. Plot border rows are recommended when evaluating characters subject to inte rhybrid competitive influences. An alternative approach is using one-r ow or two-row arrangements and grouping hybrids similar in plant heigh t and maturity in the same field proximity.