EARLY GENERATION TESTING AS A MEANS OF PREDICTING THE VALUE OF SPECIFIC CHROMOSOME SUBSTITUTIONS INTO COMMON WHEAT

Abstract

Two experimental methods were used in an attempt to establish tests by which the value of whole chromosomes for substitution could be determined. The first of these, the F₁ method, depended on the comparison of the performance of reciprocal F₁ monosomic × disomic hybrid combinations, in which the univalent chromosome from the two different sources was tested against the uniform genetic background provided by the F₁ hybrid. The second method, the F₃ bulk method, involved the establishment of the chromosome pair under test in a pure state in a F₃ hybrid bulk by the use of the appropriate monosomic line. This material was tested against the F₃ hybrid bulk of the parental varieties in which all the chromosomes were freely segregating, and also against existing substitution lines.The F₁ method demonstrated marked differences between homologous chromosomes of different varieties when they were tested in the univalent condition for the characters investigated. From these differences the homologous chromosomes of the varieties could, in some cases, be arranged in a linear order of performance, an order which may indicate their relative contribution if they were used in the production of substitution lines.The F₃ bulk method did not reveal appreciable differences between the chromosome lines studied and therefore could not be used as a predictive method.