GENETIC-VARIATION AND SELECTION CRITERION FOR DIGESTIBILITY TRAITS OFFORAGE MAIZE

Variations in feeding value characteristics were studied on a factoria l mating design, within a multilocal network. The in vitro digestibili ty of dry matter (IVDDM), neutral detergent fiber (NDF), acid detergen t fiber (ADF), acid detergent lignin (ADL), starch, soluble carbohydra te, protein and ash contents were evaluated on whole plant samples. Th e in vitro digestibility of the non- starch and non- soluble carbohydr ate plant part (IVDNSC) was also computed from near infra-red reflecta nce spectroscopy estimations of IVDDM, starch and soluble carbohydrate contents. Variations due to general combining ability (GCA) were more important, for all traits, than variations due to specific combining ability (SCA). Variations due to the GCA x environment interaction wer e also sizeable and were partly explained by the earliness of the line s. IVDDM was primarily influenced by the relative proportions of cell walls and starch in the whole plant, which were particularly susceptib le to the development stage of the plants, at harvest. When adjusted f or earliness, there was generally no significant relation between the line per se value and GCA performance in the biochemical constituent c ontents of the plant. On the contrary, IVDNSC seemed to be a feeding v alue trait worth evaluating at the inbred line level. It was also almo st independent of the ripening stage and could be easily computed from whole plant samples. IVDNSC, with a simultaneous control of starch co ntent, might be a good selection criterion for evaluating and improvin g the nutritive value of forage maize.