SELECTING WINTER FACULTATIVE WHEAT GENOTYPES FROM SPRING X SPRING CROSSES (REPRINTED FROM WHEAT - PROSPECTS FOR GLOBAL IMPROVEMENT, 1998)/

F-2 populations derived from a half diallel cross between 11 spring br ead wheat cultivars were classified according to segregation for headi ng date in a spring environment. Seventeen populations segregated very late plants, presumably of winter type, resulting from the presence o f different Vrn genes in the parents. The objective of the study was t o evaluate the performance of these spring x spring crosses grown in a winter wheat environment. F-2 plants were selected from six populatio ns and were simultaneously exposed for several generations to the wint er wheat environment (Toluca, Mexico, winter) and spring wheat environ ment (Ciudad Obregon, Mexico, winter; Toluca, spring). Visual selectio n was conducted on F-3-F-5 populations for agronomic type relevant to the environment under which the segregating generations were grown. Th e lines grown in the spring environment performed very well and a numb er of them were promoted to advanced generation testing. The same line s 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.