Genetic variability for feeding value of faba bean seeds (Vicia faba): Comparative chemical composition of isogenics involving zero-tannin and zero-vicine genes

In a preliminary experiment, 74 faba bean genotypes including winter genoty pes (autumn-sown) and spring genotypes (spring-sown) and isogenic populatio n pairs (tannin-containing v. tannin-free and vicine/convicine-high v. vici ne/convicine-low), were analysed for the chemical composition of their seed s. A large variability was found for the main constituents (starch, protein and fibre). Autumn-sown genotypes contained 2.3 % less proteins but 2.5 % more starch in the seed dry matter (DM) than spring-sown genotypes. The ve gene, which lowers the vicine and convicine contents, did not significantly modify the main seed components in the isogenic comparisons. The ttl and z t2 genes, which eliminate condensed tannins in the seed coats, lowered by 2 .1 % the proportion of the seed coat in the DM. In the isogenic comparisons , the zt2 gene had a stronger effect than ttl in reducing the total seed fi bre and increasing the protein content. In a second experiment, from the original 74 genotypes, 12 contrasted genot ypes were selected and multiplied for animal nutrition trials. Their chemic al analysis confirmed the variability between the faba bean categories obse rved in Expt 1, but detailed chemical analyses illustrated the variability in amino acid, fatty acid, amylose and oligosaccharide composition, trypsin inhibitory activity, condensed tannins, lectins and phytic phosphorus cont ents.