A further comparison is obtained from the 108 crosses from which material was grown for selection by both the pedigree and the bulk method. The latest generation by which all progenies from an individual cross were rejected was for (a) : the number of drosses from which selections were taken by both methods and (b) : the number of crosses from which selections were taken by the pedigree method only, the material grown for the bulk method being rejected before reaching the F₁₀ generation.


For example, there were 22 crosses in which no selections were obtained from the bulk line, and in which some selections by the pedigree method survived up to F₆ but were rejected by F₇.

Material from crosses made after 1941 is still under test. The total number of crosses made between 1927 and 1956 was 754 (many crosses were repeated several times) and the total number of hybrid bulks started was 269.

Two high yielding varieties, recently released, have been bred by the pedigree method :-

Arawa : The average percentage increase over the standard variety was 17%, in 61 large replicated field trials, sown in different districts, over 6 seasons.

Aotea : The average percentage increase over the standard variety was 22%, in 85 large replicated field trials, sown in different districts, over 8 seasons.

The immediate effect of these varieties on the breeding programme has been the raising of the yield standard for wheat trials and the rejection of the majority of the progenies in the various stages of testing. For this reason the hybrid bulk method has been abandoned for general wheat breeding as it does not keep pace with the production of new high yielding varieties in various parts of the world. Selection by the pedigree method from crosses with these new wheats as parents may result in further increases in yield which will be achieved more rapidly than by the hybrid bulk method.

Compound crosses. The use of F₁ generations as parents for further crosses widens considerably the variation expected in F₂ and allows for the selection of combinations of the attributes of four or more parents. Frankel in 1936, made his first compound cross which involved four distinct varieties. This practice, the use of F₁ generations as parents for further crosses, was continued at the Wheat Research Institute and later at the Crop Research Division to which wheat breeding was transferred. The two new wheats, which have produced large increases in yield, were both derived from compound crosses.

(Received May 11, 1957)