Self-sterility, self-fertility, inbreeding and heterosis; genetical interpretation and application in pasture plant breeding

Abstract

It is not the object of this paper to supply specific information on the behaviour of pasture plants under various conditions of fertilization. I shall attempt to review some of the results obtained in work on various organisms, in the search for those principles which are fundimental to the phenomena forming the subject of this paper; fundamentals which, I admit, may not generally allow of a direct application in economic plant breeding, but which may, lead the way to new ideas and to new methods of procedure. There is one idea fundamental to modern crop biology: that the biological constitution of any crop should be controlled. Needless to say, this does not imply that all crops should be uniform, consisting of one pure line of one species. But whether 8 plant population consists of one variety of one species- as in most agricultural crops - or of an association of a number of species - as in most pastural crops - we ask that any individual Component, species,variety or strain, be biologically "controlled", i.e. its members should be reasonably uniform in a genetic sense. It appears to me that our present ideas are perhaps not the last word on crop constitution; that even in our agricultural crops; particularly in those with dense spacing, plant associations of closely related forms might be superior to the single lines constituting our present crop varieties. But this would only on the surface mean a reversion to the mixed crops of days gone by-: each constituent would be biologically stable, its performance known; alone and in co-operation with others, and the composition and relative prevalence in the mixture would be controlled.