Growth and Development in Range Grasses. V. Photoperiodic Responses of Clonal Divisions of Three Latitudinal Strains of Side-Oats Grama

Abstract

1. Clonal divisions of twelve selected individuals of each of three strains of side-oats grama were grown from April 16 to November 17, 1944, on Chicago natural daylength and on photoperiods of 13, 14, and 15 (or more) hours. The three strains from Texas (San Antonio), Oklahoma (El Reno), and North Dakota (Cannonball) represent the extremes and approximate means of latitudinal origin and range of response of twelve strains previously grown over a 2-year period on 9-, 13-, 16-, 20-hour, and natural photoperiods. The selected individuals sampled the diversity of each strain. 2. All clones from Texas flowered rapidly and persistently on 13-hour photoperiod, and in late September on natural photoperiod. Some flowered weakly in September and October in the 14-hour series. None flowered in the 15-hour series. Vegetative growth was vigorous on all treatments. These clones are intermediate- or short-day plants with an upper critical photoperiod for rapid and vigorous flowering between 13 and 14 hours. All clones from North Dakota grew and flowered vigorously on natural, 14-, and 15-hour photoperiods. On 13-hour photoperiod growth was very limited, although some clones flowered weakly. These clones are long-day plants with a critical photoperiod for vigorous growth and flowering between 13 and 14 hours. Most clones from Oklahoma flowered equally well and fairly rapidly on 13- and 14-hour photoperiods. Most of them eventually flowered on natural photoperiod, but were delayed, in contrast to the 13- and 14-hour series. Most of them either failed to flower or were delayed in flowering on 15-hour photoperiod. These data and previous observations indicate that this strain includes both intermediate- and long-day plants, both types having a short critical photoperiod between 9 and 13 hours. One of the former has an upper critical photoperiod between 14 and 15 hours. 3. Such strong photoperiodic differentiation and adjustment have seldom been reported within a single native species. The series of photoperiodic types within it raises interesting questions as to the evolution and nature of the responsible genetic and physiological mechanisms, since the species probably originated in low latitudes, where the short-day response is typical, with subsequent adjustment to the longer days encountered in the northward extension of its range. Other implications of the findings discussed in this or the preceding paper (6) concern some of the causes of the morphological diversity among the latitudinal strains when grown together, as reported by other workers, and the bearing of photoperiodic adjustment upon possible acclimatization of strains to latitudes lower or higher than their native ones.