Semiexotic population of corn Mo17xAcross 8443 La Posta as a base for forage breeding

Little information about genetic variation in exotic or semiexotic forage p opulations is available, making it difficult to calculate the expected bree ding advances in this type of germplasm. Thus, the semiexotic population Mo 17 x Across 8443 La Posta was studied to (i) estimate the quantitative gene tic parameters for forage traits and (ii) evaluate this germplasm as a base for forage breeding programs. One hundred and fifty full-sib families, dis tributed in fifty half-sib families were studied over two years at a single location. Heritability estimates for days to pollen shedding (0.69), numbe r of leaves (0.78), ear height (0.54), plant height (0.47), and ear height/ plant height (0.40) were greater than those found in many Corn-Belt populat ions, while stem diameter showed an h(2) of 0.29. The stover nutritive qual ity trails presented low heritabilities (between 0.09 and 0.15). Heritabili ty of ear yield was not significantly different from zero and h(2) of stove r production was 0.44. Positive additive genetic correlations were found am ong days to flowering, all studied morphological traits: stover yield and t otal dry matter yield. Total digestible dry matter yield showed significant correlations with stem diameter, plant height and production traits, while nutritive quality traits were not correlated with morphological or product ion traits. Improvement of the semiexotic population should lower ear heigh t and increase stover digestibility and yield, while avoiding further lengt hening of the maturity range. Indirect selection through stem diameter and plant height are suggested as means of increasing total digestible dry matt er yield, as direct selection for this trait seems very difficult.