SCREENING TROPICAL MAIZE POPULATIONS TO OBTAIN SEMIEXOTIC FORAGE HYBRIDS

In mild Mediterranean irrigated zones, it is possible to grow late forage maize hybrids (900-1000 United Nations Food and Agriculture Organization [FAO]). These late hybrids should give higher yields than available commercial hybrids (700-800 FAO). This study was conducted to (i) assess whether semiexotic (adapted x tropical) materials would be a viable source of high-yielding late forage hybrids, (ii) determine the most suitable exotic populations for a breeding program, (iii) evaluate the most important production-and/or quality-related traits for selection. 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. Twenty-seven semiexotics yielded more total digestible dry matter than did B73 x Mo17, and seven semiexotics outyielded Pioneer 3183. Higher stover yields, good ear production, and similar stover digestibility are responsible for these results. The B73 testcrosses performed better than Mo17 testcrosses for total digestible dry matter, mainly because of better earyield. The best-performing semiexotics included Tuxpeno and Cateto germplasm. Correlations and multiple regression analysis showed 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 digestibility is probably responsible for the low influence on total digestible dry matter. Increases in stover digestibility should be possible without reducing biomass production because production traits and stover digestibility were not correlated.