Selecting winter/facultative wheat genotypes from spring x spring crosses

F sub(2) populations derived from a half diallel cross between 11 spring bread wheat cultivars were classified according to segregation for heading date in a spring environment. Seventeen populations segregated very late plants, presumably of winter type, resulting from the presence of different Vrn genes in the parents. The objective of the study was to evaluate the performance of these spring x spring crosses grown in a winter wheat environment. F sub(2) plants were selected from six populations and were simultaneously exposed for several generations to the winter wheat environment (Toluca, Mexico, winter) and spring wheat environment (Ciudad Obregon, Mexico, winter; Toluca, spring). Visual selection was conducted on F sub(3)-F sub(5) populations for agronomic type relevant to the environment under which the segregating generations were grown. The lines grown in the spring environment performed very well and a number of them were promoted to advanced generation testing. The same lines grown in the winter environment suffered from frost and were almost entirely discarded, proving that spring x spring crosses have limited value for germplasm improvement targeted for conditions similar to the Toluca highland winter environment.