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Effects of Daylength and Gibberellic Acid on the Creeping‐Rooted Habit of Alfalfa 1
Author(s) -
Carlson G. E.,
Sprague V. G.,
Washko J. B.
Publication year - 1964
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1964.0011183x000400040020x
Subject(s) - agricultural experiment station , habit , gibberellic acid , crop , library science , biology , agriculture , agronomy , ecology , psychology , germination , psychotherapist , computer science
T HE formation of stems on roots of creeping-rooted alfalfa, Medicago sativa L., not only is interesting, but also affords new opportunties to forage programs. Full utilization of the potential of creeping-rooted alfalfa will depend not only on the development of adapted varieties but also on sound management practices based on a thorough understanding of the physiological processes involved in stem formation on roots. Expression of the creeping habit of alfalfa was reduced by competition from grass3 and increased by short days and cool temperatures (2). The number of adventitious stem sites on roots of alfalfa from which adventitious stems arise was decreased by defoliation and increased by short days (1). The number of sites was in part a function of root size, but the differential response of site production to photoperiod and defoliation appeared to be result of undefined physiological effects on the tops (1). Photoperiod may affect directly site production, or it may first affect another growth response such as top growth, which in turn affects site production. Photoperiod may differentially affect the production or destruction of site-promoting or siteinhibiting substances. Murray (9) X-radiated tops of rooted creeping-rooted alfalfa cuttings and observed that more adventitious stems were produced in less time by the nonX-radiated cuttings. These results suggest that an unknown X-radiation effect, which stimulated adventitious stem formation, was translocated to the roots. Skoog (10) demonstrated auxin inactivation and inhibition of auxin formation by X-radiation. Increased tillering of plants under short daylengths was attributed to decreased auxin content (5). Results of a previous study indicated that top growth and site formation of alfalfa were affected markedly by daylength (1). The dependence of these processes on a common photoperiodic reaction and their relation may be evaluated if the short-day growth habit of tops were reversed by gibberellic acid (GA). Gibberellic acid is known to promote stem elongation (12), and a preliminary trial with alfalfa indicated that applications of GA to [plants grown on short days. produced the long-day habit ottop growth. The oblectives of these studies were to measure and compare rates of site formation and top and root growth of two clones with differing degrees of responsiveness to short days, and to measure the relation of GA reversal of the short-day growth habit of tops to site production.