SCREENING TROPICAL MAIZE POPULATIONS TO OBTAIN SEMIEXOTIC FORAGE HYBRIDS

In mild Mediterranean irrigated zones, it is possible to grow late for age maize hybrids (900-1000 United Nations Food and Agriculture Organi zation [FAO]). These late hybrids should give higher yields than avail able commercial hybrids (700-800 FAO). This study was conducted to (i) assess whether semiexotic (adapted x tropical) materials would be a v iable source of high-yielding late forage hybrids, (ii) determine the most suitable exotic populations for a breeding program, (iii) evaluat e the most important production-and/or quality-related traits for sele ction. Testcrosses of 44 tropical populations by B73 and Mo17 adapted inbreds were evaluated. Field trials, which included three sets of top crosses, were carried out in Northeast Spain. The hybrids B73 x Mo17 (700 FAO) and 'Pioneer 3183' (800 FAO) were used as common checks. Twe nty-seven semiexotics yielded more total digestible dry matter than di d B73 x Mo17, and seven semiexotics outyielded Pioneer 3183. Higher st over yields, good ear production, and similar stover digestibility are responsible for these results. The B73 testcrosses performed better t han Mo17 testcrosses for total digestible dry matter, mainly because o f better earyield. The best-performing semiexotics included Tuxpeno an d Cateto germplasm. Correlations and multiple regression analysis show ed that total digestible dry matter depends mainly on ear yield, to a lesser extent on stover production, and little on stover digestibility . The low genetic variability among populations for stover digestibili ty is probably responsible for the low influence on total digestible d ry matter. Increases in stover digestibility should be possible withou t reducing biomass production because production traits and stover dig estibility were not correlated.