Seasonal root changes and their relationships to leaf production and persistency of growth in some grasses and clovers : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Field Husbandry at Massey University, by 550 [D.E. Yen]

The seasonal behaviour of pasture plant species is of fundamental importance to the farmer as one of the indices of value of any particular species, and the uses to which it can be put; and to the plant breeder, since it is his primary object to produce pasture plants which suit the farmer under his particular system of farming. To illustrate this point specifically, the example of the ideals aimed at in the breeding of short rotation ryegrass in New Zealand may be cited. Quoting Levy (1945), "... Italian ryegrass is a one- to two-year plant for the temporary pasture, and the true perennial ryegrass can be used widely in rotational and permanent pastures. There is, however, too large a gap between true perennial ryegrass and true Italian ryegrass, and many years of breeding and selection within these species accentuated the gap rather than reduced it." It can be seen that the short rotation system of farming, incorporating pasture leys of 3-4 years was not well served in the choice of a suitable ryegrass. Thus the plant breeding section of the Grasslands Division (Department of Scientific and Industrial Research) turned its attention towards breeding by hybridisation of perennial and Italian ryegrass, a type that would possess as far as possible the desirable qualities of these two species in combination; that is, it would combine some of the rapid establishment, high winter and early spring growth and palatability of Italian ryegrass with an appreciable degree of persistency of perennial ryegrass. Seasonal growth thus played the major part in the objectives of the resultant programme from which short rotation ryegrass was produced. Comparative trials of yields of the three grasses, perennial, Italian and short rotation ryegrasses were conducted in different localities, serving a very important purpose in providing farmers with direct information regarding the seasonal characteristics of production of the new type. These trials, which are continuing, show that short rotation ryegrass conforms largely to the objectives aimed at, so that the requirement s of the man farming under short rotation system have been met, to a great extent, by the work of the plant breeder. [From Introduction