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The effect of genetic removal of condensed tannins on the levels of other antinutritional factors in faba beans (Vicio faba L.) has been studied by comparison between partners of six near-isogenic pairs for trypsin inhibitor activities (TIA), concentrations of lectins and pyrimidine glucosides (vicine and convicine), seed weight, and the proportion of testa thereof. Each near-isogenic pair consisted of two lines which were genetically almost identical, apart from the absence [tannin-free (TF)] or presence [tannin-containing (TC)] of condensed tannins. Within these pairs no effect of tannin content was observed on cotyledon-bound TIA or lectin concentrations. Seeds of the TF lines showed higher levels of pyrimidine glucosides, lower seed weight, and lower proportion of testa as compared to the TC lines of the same near-isogenic pair. Methanolic extracts from testa of exclusively the TC lines showed significant TIA with both porcine and bovine trypsin. This TIA was completely inhibited by 1% poly(vinylpyrrolidone). These data indicate that condensed tannins are responsible for the testabound TIA. The observations are discussed in relation to the consequences of breeding faba beans, free of condensed tannins, for the agricultural characteristics and for the nutritional quality of the crop.

The effect of breeding for the absence of condensed tannins in the testa of Vicia faba L. on resistance to foot rot, Ascochyta blight and chocolate spot diseases was investigated in 1988-92 at Wageningen, The Netherlands. For this purpose the disease development in tannin-free and tannin-containing partners of six near-isogenic pairs was compared after exposure to causative pathogens. Except for one near-isogenic pair, in which both partner lines showed a relatively high resistance, the tannin-free lines were more susceptible to foot rot than the tannin-containing partners of the same pair. This observation indicates that the presence of condensed tannins in the testa prevents infection of the plant by the causative pathogens. Fusarium oxysporum and F. solani, isolated from faba bean tissues showing foot rot symptoms, were shown to be primary foot rot pathogens, while F. avenaceum caused wilting of young plantlets. No pathogenic isolates were obtained from F. tabacinum. Resistance to Botrytis fabae (chocolate spot disease), scored on leaves and stems under glasshouse and field conditions in 1992, was not influenced by selection for the absence of condensed tannins which occur in the testa of mature seeds. Under the same environmental conditions, leaves, stems, pods and seeds of tannin-free lines showed similar levels of damage due to Ascochyta fabae (Ascochyta blight) as the tannin-containing partner lines of the same near-isogenic pair. These results indicate that condensed tannins do not play a role in resistance to both B. fabae and A. fabae, probably because, except for the seeds, these polyphenols do not accumulate in the tissues affected by these pathogens.

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