Indirect selection for total digestible dry matter yield in forage maize, using stem diameter

Abstract

Breeding for increased Total Digestible dry matter yield (TDdmy) in forage maize presents problems due to trait complexity, low heritabilities of its components, and difficulty of some analysis. Consequently the use of indirect selection would be an alternative procedure in order to advance in this character. Previous studies on several morphological traits pointed to the diameter of the first stem elongated internode as a good trait to select. This diameter has an acceptable heritability (h2=0.37), is positively correlated with yield (r=0.52), is not negatively correlated with nutritive quality, and can be measured before flowering, thus allowing to make crosses among the selected plants. To check this in a practical manner five cycles of mass selection were undertaken in Lancaster variety. The comparative study of the five selected generations and the base population yielded the following results: a) a constant increase in stem diameter of about 4% per generation, b) a constant increase of stover yield, and an increase of ear yield interrupted at the third cycle of selection, c) no changes in stover digestibility but a 24% increase in TDdmy at the end of the process, due to the increase in biomass yield, d) a 4.4% increase in days to flowering at the end of the process. Although the correlated response of the ear yield stopped at the third cycle of selection it is concluded that stem diameter is a good trait to select in order to improve TDdmy.