In vitro digestibility of the testa in tannin-free field beans (Vicia faba L.)

Abstract

SummaryThe seed-coat of all white-flowered varieties of Vicia faba and segregants tested was free of tannin. In two field trials, the whole grain of white-flowered varieties wassignificantly higher in in vitro digestibility of the dry matter, on average 4·7% higher, than coloured-flowered varieties of similar seed size. In subsequent trials where the testa and cotyledon were examined separately, this difference was shown to be largely due to a mean D value (digestibility of the organic matter) of the testa in tannin-free varieties of 56·4% compared with 17·2% in tannin-containing varieties. Seed size was positively correlated with D value but not because of differing proportions of testa.Differences between varieties in acid-pepsin solubility and protein content of the testa were much smaller and not associated with presence of tannin. The testa colour of some tannin-free F2 plants was a darker shade of grey than either parental population. An inbred line completely lacking in anthocyanin in flowers and stem but with the normal black wing spot had tannin in its testa.Grains of peas from the coloured-flowered variety, Minerva, reacted to a tannin test wheieas those from white-flowered varieties, Greenshaft and Flavanda, did not.The case for breeding further tannin-free varieties of Vicia faba is discussed.