The Progeny Test and Methods of Breeding Appropriate to Certain Species of Crop Plants

Abstract

Methods of procedure in breeding self-fertilized species of crop plants have been fairly well standardized. The same can not be said with reference to cross-fertilized crops. The latter include such widely different species as corn, alfalfa, red clover, timothy and many other grasses and legumes. These vary greatly in their mode of reproduction and breeding behavior. Improvement of these species presents a variety of problems, depending on how they are to be cultured and utilized. Methods of breeding should be used, which are appropriate to the species concerned and the objective to be attained. Breeding methods commonly employed can be grouped under three headings-selfed line breeding, strain building and mass selection. These are discussed and compared with respect to their applicability to different species and specific problems. "Selfed line breeding" has been employed most extensively in corn improvement. Although apparently well adapted to this crop, it has only a limited usefulness in the breeding of herbage plants. "Strain building" involves the crossing of few or many carefully selected parent plants. It admits of different systems of mating and aims to maintain vigor of growth by bringing into the strain as wide a range of genotypes as possible, as far as this is consistent with progress toward the desired result. Inbreeding may be detrimental in so far as it tends to narrow the lines of inheritance and restrict the range of adaptation of the strain. In nature there exists within the species definite hereditary habitat types which represent the genotypical response of the species-population to a particular habitat. "Mass selection" provides a ready means of capitalizing on the work which nature has accomplished. The progeny test provides the only reliable method of evaluating the breeding potentialities of parent plants. The information to be gained from such tests differs greatly in significance and precision depending on whether the progeny is grown from selfed seed or from hybrid seed of crosses between homozygous or heterozygous individuals. It is of supreme importance that progenies shall be subjected to the incidence of those environmental factors which presumably may influence the success of the new production.