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

Abstract

Clonal divisions of 12 selected individuals of each of 3 strains of side-oats grama, (Boutelova curtipendula) were grown from Apr. 16 to Nov. 17,1944, on Chicago natural daylength and on photoperiods of 13, 14, and 15 (or more) hrs. The 3 strains from Texas (San Antonio), Oklahoma (El Reno), and N. Dakota (Cannonball) represent the extremes and approx. means of latitudinal origin and range of response of 12 strains previously grown over a 2-yr. period on 9-, 13-, 16-, 20-hr., and natural photoperiods. The selected individuals sampled the diversity of each strain. All clones from Texas flowered rapidly and persistently on 13-hr. photoperiod, and in late Sept. on natural photoperiod. Some flowered weakly in Sept. and Oct. in the 14-hr. series. None flowered in the 15-hr. 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 hrs. All clones from N. Dakota grew and flowered vigorously on natural, I4-, and 15-hr. photoperiods. On 13-hr. 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 hrs. Most clones from Oklahoma flowered equally well and fairly rapidly on 13- and 14-hr. photoperiods. Most of them eventually flowered on natural photoperiod, but were delayed, in contrast to the 13- and 14-hr. series. Most of them either failed to flower or were delayed in flowering on 15-hr. 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 hrs. One of the former has an upper critical photoperiod between 14 and 15 hrs. Such strong photo-periodic differentiation and adjustment have seldom been reported within a single native species. The series of photo-periodic types within it raises interesting questions as to the evolution and nature of the responsible genetic and physiol. 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 [see B. A. 19(2): entry 3674] concern some of the causes of the morph. diversity among the latitudinal strains when grown together, as reported by other workers, and the bearing of photoperiodic adjustment upon possible acclimatization of strains of latitudes lower or higher than their native ones.