Sterility in Wheat Hybrids. I. Sterility Relationships and Endosperm Development.

Partial or complete sterility is of frequent occurrence in species crosses. Within the same genus certain species are sterile when crossed while ather combinations are completely fertile. Partial sterility may cause the elimination of certain classes of gametes and prevent desired recombinations of characters in the second generation. Sterility may also cause an abnormal vegetative development. It is therefore desirable to determine the sterility relationships of the species of economic genera. The present study of the genus Triticum will include: (1) the endosperm development in fertile and sterile crosses; (2) sterility in species crosses as determined by grains set and pollen counts; (3) hybrid vigor of F, plants in relation to sterility; and (4) size and variability of pollen grains in parents and F1 plants. The second generation of species crosses and the cytological basis for sterility in wheat crosses will be treated later. The species of wheat are divided by SCHULZ (see VON TSCHERMAK 1914) into three groups as follows: