The environmental control of growth in creeping-rooted lucerne

For many years plant breeders have been trying to develop a persistent pasture legume for the Great Plains of the U.S.A. and Canada, and more recently for the drier areas of Australia and New Zealand. Of the legumes tested in the Prairie region, lucerne has proved to be the most productive and persistent. However, even the hardiest of the common varieties do not persist through a series of dry years. Recently, creeping-rooted lucerne was introduced into New Zealand as a possible variety for use in the drier areas. In its introduced form it was found to be too low producing to become an important economic variety but by crossing with the higher producing Medicago Sativa types and selecting for creeping habit it is hoped to evolve better strains. It is felt that higher producing strains of creeping-rooted lucerne could have an important place in the drier areas of Canterbury and Otago, and possibly solve the legume problem in the high country, if it could be successfully established. Creeping-rooted lucerne has horizontal roots from 4-6" underground which are capable of producing adventitious shoots at intervals along their length. These serial shoots either develop a root system of their own or rely on the parent root. (Fig. 2, Page 3) The plants spread readily without moist surface conditions. The phenomenon of adventitious shoot formation on roots is an interesting one. As Torrey (1958) points out, “the capacity for endogenous bud formation is a distinctive character of relatively few groups of plants, and involves a mechanism about which we have very little physiological knowledge”. Previous workers have dealt almost entirely with shoot production on root segments isolated from the parent plant. Although this is a convenient method for testing the potential of root segments to produce adventitious stems, and studying their formation, its value is somewhat limited. It was felt that a wider understanding of the problem would be obtained if adventitious shoot production on the roots was studied in relation to the physiology of the whole plant. This study therefore deals with the effects of environment on the growth of the plant as a whole, with particular reference to the creeping-rooted habit