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Cyclic Flowering Patterns in Flax as Influenced by Environment and Plant Growth Regulators¹

Studies were conducted to determine the mechanism which regulates flowering pattern in flax (Linum usitatissimum L.). CI 1303 flax produced flowers in cycles with distinct blossoming periods separated by brief rest periods (20 days) when grown in the field or in green. house and growth chamber environments in nutrient solution. Removal of bolls at the end of the first flowering period caused prompt renewal of flower production. Daily flower removal resulted in continuous flowering without rest periods and without plant senescence. An increase in light intensity from 14,300 to 25,500 lux in. creased seed production in the first flowering period, but further increase to 31,900 inx produced no additional increase in yield. Enhancement of CO2 level to 1270 ppm increased flower, boll, and seed production in the first flowering peirod. The plants flowered in cycles in spite of high light and CO2 levels.

Buds excised from the panicle and main-stem and cultured in vitro produced shoots and then, in 4 to 30 days, produced flowers. Blossoms were produced even by buds which are normally inhibited in the intact plant. Maximum flower counts were obtained from buds isolated at the beginning of a flowering period. Auxins and gibberellin added to the medium at 5 or I0 ppm levels inhibited flower development. It is concluded that cyclic flowering is causally regulated by hormonal systems, but the number of flowers produced in each flowering period is limited by nutritional factors and rate of plant senescence.

Key Words: Light intensity • Carbon dioxide enrichment • Flower bud development • Senescence • Auxin • Gibberellin • Tissue culture

² Former Graduate Assistant, South Dakota State University (present address: 1890 Parkway Drive, Anchorage, AK 99504); and Plant Physiologist, North Central Region, ARS, USDA Brookings, SD 57006, respectively

Received for publication November 7, 1972.