Flowering of Smooth Brome Grass Under Certain Environmental Conditions

Abstract

1. Flowering and growth responses of thirteen diverse clones of smooth brome grass were studied in greenhouse experiments, supplemented by observations made on plants established in the field, conducted during the winter and spring of 1946 and 1947. 2. In early 1946, clonal divisions, consisting of single sections of rhizomes, were grown on Chicago natural daylength and light intensity and on 17-, 15-, and 13-hour photoperiods under fluorescent lamps providing relatively high light intensity and under incandescentfilament lamps providing relatively low light intensity. Flowering first occurred approximately 1 month after bringing the plants in from the field in early January. Earliest and most prolific flowering and most vigorous vegetative growth occurred on 17-hour photoperiod under fluorescent light. The number of elongated tillers was directly, and of unelongated tillers inversely, correlated with length of photoperiod. Rhizome production was not obviously affected by photoperiod but was strongly affected by light intensity. 3. Plants were brought in from the field on August 31, 1946, and again on December 27 after exposure to low temperatures. Clonal divisions of both groups of plants, consisting of pieces of entire plants, were grown on 18- and 13-hour photoperiods under fluorescent lamps, beginning January 7, 1947, and on natural daylength. Flowering of the 18-hour December plants occurred in approximately 3-4 weeks after differential photoperiodic treatments were begun. One December plant on 13-hour photoperiod flowered. No December plants on natural daylength had flowered by June 1. None of the August plants flowered under any treatment, but all on long photoperiod showed marked tiller elongation. Increase in number of tillers was greatest for the August plants on natural daylength, least for those on 18-hour photoperiod, Of the December plants, the series on natural daylength produced most new tillers, plants on 13-hour photoperiod least. Dry weights of tops of both August and December plants were greatest in the 18-hour series, of roots in the 13-hour series. Height in both August and December plants was greatest in the 18-hour series, least in the series on natural daylength. Fully viable seed was produced on the 18-hour December plants under the relatively poor growing conditions of a Chicago winter in the greenhouse. 4. Floral primordia were present on plants growing in the field at Chicago in early April. A 13-hour photoperiod inhibited their subsequent normal development and elongation. 5. The vegetative and flowering responses showed no apparent correlation with place of origin of the clones.