Shoot development in lucerne : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Agricultural Science in the University of Canterbury [Lincoln College]

Abstract

In recent years there has been an upsurge of interest in lucerne as a pasture plant for prazing, either sown alone of in a mixture. This has been accompanied by an increased interest in the effect of a higher proportion of M. falcate genes on the agronomic characteristics of lucerne. Since M. falcate is tolerant of more extreme environments than M. sativa, the infusion of M. falcate germ plasm into lucerne breeding programmes has conferred several advantages. The most notable of these has been the breeding of creeping lucernes, both rhizomatous and creeping rooted types having been developed. The available evidence suggests that not only are the creeping lucernes more tolerant of grazing than non-creeping cultivars, but they can be of special value in environments subjected to drought or extreme winter conditions. In an attempt to even out seasonal variability on light soils, several cultivars of lucerne were sown at Ashley Dene, in a mixed sward under grazing conditions in 1950 (Iversen 1965, 1967). Yields were increased from the 3500 lb D.M./acre normally achieved on this soil type, to 5000 lb D.M./acre, with reduced variability. Within five years the standard New Zealand cultivar (Wairau) had thinned to nothing, several other strains were little better, but Glutinosa, a rhizomatous creeper, persisted well and was still thriving after sixteen years (Iversen 1967). In 1954 the Plant Science Department at Lincoln College commenced an improvement programme with Glutinosa, aiming to produce a grazing type lucerne more suited to the Canterbury environment. The final selection of six parents was made in 1963 and the first seed obtained in 1964. Since then a number of field trials comparing College Glutinosa and Wairau in various environments, have shown that College Glutinosa can be a valuable alternative to Wairau, especially as a grazing plant (J.G.H. White, pers.comm). Little work has been done to investigate the responses of College Glutinosa to variations in environment or management systems. The present study was designed to obtain information on the normal pattern of crown development under simulated sward conditions. The pattern of shoot formation and development was also studied more fully under controlled environment conditions in growth cabinets.