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Planting Date Effects on Sunflower Head and Seed Development¹

The effects of environmental conditions during sunflower (Helianthus annuus L.) seed development and maturation on the final oil percent of seed and composition of the oil have been studied extensively but little is known about the sequential changes that occur in seed and oil during seed development and maturation. A better understanding of these changes could lead to improved management of sunflower for seed and oil production. The objective of this study was to determine the influence of planting date on development and maturation of sunflower head and seed. Sunflower was planted in about 2-week intervals from 23 Mar. to 1 Aug. 1977 in field plots on Pullman clay loam (fine, mixed, thermic Torrertic Paleustolls). The experiment had a randomized block design with three replications. Plants that were at the same stage of development were marked at the ray flower stage. After anthesis, head samples were collected two or three tunes each week for about 30 days to determine head weight and diameter; seed dry matter percent, weight, and oil percent; and oleic and linoleic acid concentration of the oil. Separate seed samples were obtained from the outer, middle, and inner sections of the heads. Planting date, sampling date, and head position, as well as the interactions of these variables, significantly affected all dependent variables. Head diameter and fresh weight initially increased as the sunflower developed, then decreased due to head shrinkage and drying as the sunflower matured. Seed dry matter percent increased from the first to last sampling, but not at the same rate for all planting dates. Trendsfor seed weight were similar to those for dry matter. Total oil percent of seed increased from the first to the seventh sampling after which the differences were not significant. Seed from late plantings generally had a low oil percent, but seed from the ninth planting had an unexplained high oil percent. Oleic and linoleic acid concentrations of the oil decreased and increased, respectively, for later plantings. These trends also occurred with later samplings of sunflower planted on a given date. Based on multiple regressions, air temperature significantly influenced changes per day in seed oil percent, but not the oleic and linoleic acid concentration of the oil, during the intervals between samplings. During these intervals, changes in oleic and linoleic acid concentration of the oil were significantly influenced by total solar radiation and day length.

Key Words: Helianthus annuus L. • Oleic acid • Linoleic acid

² Soil scientist, USDA Conservation and Production Research Laboratory, Bushland, TX 79012, and research geneticist, W. R. Poage Pecan Field Station, Brownwood, TX 76801 (The second author was formerly at Bushland).

Received for publication February 9, 1981.