Growth and Development in Range Grasses. III. Photoperiodic Responses in the Genus Bouteloua

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Abstract
Lots of 100 plants each of side-oats grama (B. cur-tipendula), slender grama (B. filiformis), Rothrock''s grama (B. rothrockii), hairy grama (B. hirsuta), black grama (B. eriopoda), and blue grama (B. gracilis) were grown continuously for 41/2-5 months after germination on Apr. 6 on photoperiods of 16, 12, and 8 hours in the Univ. of Chicago greenhouses. Reciprocal transfers were then made among treatments, both with and without simultaneous clipping of the tops, and the plants were allowed to grow for another 4-6 months. Southern Arizona, except for blue grama from Montana, was the seed source of all spp. Growth and flowering responses showed definitely that these strains of slender and side-oats grama, which belong to the same subgenus (Atheropogon), are typical short-day plants, most individuals failing to flower on a 16-hr. photo-period. A "critical photoperiod" expt. showed this value to lie between 14 and 141/2hrs. The other 4 spp., belonging to the subgenus Chondrosium, made less decisive flowering responses. The species with strains from Arizona were considerably delayed in flowering on the longest photoperiod, and these strains should probably be regarded as short-day plants. Blue grama from Montana was more or less indeterminate, with some long-day tendencies in flowering behavior. The 5 spp. with strains from Arizona exhibited more or less typical short-day vegetative behavior. The total numbers of tillers, of tillers bearing inflorescences, and of crown roots were inversely correlated with length of photoperiod to a greater or less degree in most spp., while average max. height, av. dry wt. of roots and tops, and vigor of individual inflorescences were correlated positively with length of photoperiod. The effects of photoperiod should be considered in interpreting growth habits of these species in nature, and in selection and breeding programs designed to develop strains more desirable for forage production, or for use in artificial revegetation of overgrazed or denuded areas.

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