HETEROSIS IN CROSSES BETWEEN AMERICAN AND SPANISH POPULATIONS OF MAIZE

Most maize (Zea mays L.) crosses in temperature zones use the heterotic pattern Reid X Lancaster, but in western Europe the pattern U.S. dent X European flint has also been used. This study was undertaken to determine the heterotic relationships between Spanish and U.S. Corn Belt germplasm to identify a heterotic pattern for a comprehensive system of breeding. Four early U.S. Corn Belt and five Spanish populations were crossed in a diallel series that was tested for three years at two locations. Using heterosis for yield as the measure of dissimilarity, a phenogram showed the existence of three groups of populations: U.S. Corn Belt, northern Spain, and southern Spain. Two composites were formed, one with germplasm from northern Spain (EPS6) and the other with germplasm from southern Spain (EPS7), that were subjected to one cycle of S1 recurrent selection. The yield gains were 10.4 and 9.4% for EPS6 and EPS7, respectively. The mid-parent heterosis was 32.7%, much greater than predicted (17.7%). Spanish germplasm can be a useful addition to maize breeding programs of temperature zones, enhancing the genetic base of the material being used.