Genetic analysis and QTL mapping of cell wall digestibility and lignification in silage maize

Improving digestibility is a major goal for forage maize (Zea mays L.) breeding programs. Quantitative trait loci (QTL) affecting forage maize digestibility-related and agronomic traits were mapped and characterized in a set of recombinant inbred lines (RIL). Eleven traits were analyzed on whole plant samples: neutral detergent fiber (NDF), starch content (STC), crude protein content (CPC), acid detergent lignin (ADL), in vitro dry matter digestibility (IVDMD), in vitro cell wall digestibility (IVNDFD), in vitro digestibility of non-starch and non-soluble carbohydrate (IVDNSC), dry matter content (I)MC), dry matter yield (I)MY), mid-silk date (SILK), and plant height (PHT). Evaluation was performed among the RIL populations studied per se (RILps) and in combination with a tester (TC). The genetic variances (sigma (2)(g)) were highly significant and, in most cases, greater than genotype X year interaction variances (sigma (2)(gxy)). Heritabilities ranged from 0.49 to 0.70 in RILps and from 0.12 to 0.58 in TC. Twenty-eight QTL were identified among TC by CIM, which explained individually between 3.3 and 20.2% of the phenotypic variation (R-p(2)) for traits related to digestibility or agronomic performance. Twenty QTL were identified among RILps, which explained individually between 6.5 and 15.3% of the phenotypic variation (M). Seven of these QTL were common to TC and RILps. Cell wall digestibility estimates (IVNDFD or IVDNSC) were the traits with the highest number of QTL. In contrast, we detected only one QTL for dry matter digestibility (IVDMD). Thus, it may be useful to separate IVDMD into its two component parts, cell wall digestibility, which could be estimated from line per se values, and starch content. Characteristics such as IVDNSC or IVNDFD, coupled with QTL information, would be powerful tools in the search for genes involved in maize lignification or cell wall biogenesis.