Kernel modifications and tryptophan content in QPM segregating generations

Maize has poor nutritional value due to deficiency of two essential amino acids - tryptophan and lysine. Although recessive opaque2 (o2) mutation significantly increases their content in the endosperm, incorporation of opaque2 into high yielding cultivars was not commercially successful, because of its numerous agronomic and processing problems due to soft endosperm. Quality protein maize - QPM has lately been introduced as opaque2 maize with improved endosperm hardness and improved agronomic traits, but mostly within tropical and subtropical germplasm. The ongoing breeding project at MRI includes improvement of MRI opaque2 lines and conversion of standard lines to QPM germplasm. The main selection steps in QPM breeding involve assessing kernel modifications and tryptophan level in each generation. Herein, we present the results of the analysis for these traits on F3 and BC1F1 generations of QPM x opaque2, opaque2 x QPM and standard lines x QPM crosses. The results showed that the majority the genotypes had kernel types 2 and 3 (good modifications). The whole grain tryptophan content in F3 and BC1F1 genotypes of crosses between QPM and opaque2 germplasm was at the quality protein level, with a few exceptions. All BC1F1 genotypes of standard lines x QPM had tryptophan content in the range of normal maize, while majority of F3 genotypes had tryptophan content at level of QPM. The progeny (with increased tryptophan levels) of QPM and opaque2 crosses had significantly higher tryptophan content compared to the progeny of crosses between standard and QPM lines - 0.098 to 0.114 and 0.080, respectively. All genotypes that had poorly modified kernels and/or low tryptophan content will be discarded from further breeding.

Relations between ruminal and intestinal in sacco starch digestion in ruminants

The proportion of the starch that escapes rumen degradation varies from 5 to 65% of the starch intake. It depends on the feeding level and the nature of the cereal, and for a same cereal, on its endosperm hardness, related to genotype and maturity, and on the technological treatments, including particle size (Huntington et al., 2006). The intestinal digestion of starch escaping rumen degradation essentially takes place in the small intestine and varies between 15 to 85% of the starch that arrives into the duodenum. As in the rumen, this variability would essentially be due to the intrinsic features of the maize that determines the accessibility of the starch to the endogenous enzymes, in particular the endosperm hardness and the particle size. The aim of this work was to evaluate the rumen starch degradation of maize and its residue digestion in the small intestine as function of particle size and endosperm hardness.