TANNIN STRACTURE QTL · Linking tannins, biological activities and genetic maps in a unique willow germplasm collection

Linking tannins, biological activities and genetic maps in a unique willow germplasm collection

Willow (Salix spp.) leaves are of interest as a complementary animal feed, especially during summer droughts and in extensive farming systems. However, willow leaves also contain tannins, which may affect their nutritive value. This project analysed the tannin composition of 75 diverse accessions from the UK National Willow Collection at the BBSRC Rothamsted Research Institute. At the University of Reading (UK), the postdoctoral researcher successfully applied a method, which had been designed for the direct screening of tannins in an Onobrychis germplasm collection (Gea et al., 2011), to the direct screening of willow leaves. This analysis revealed that tannin content and composition varied considerably between the different willow species: total content ranged from 0.28 to 3.93 g/100 g dry matter and tannin polymer size from 1,400 to 9,450 Daltons. The ratio of procyanidin to prodelphinidin tannins varied from 12.0/88.0 to 98.7/1.3, while cis to trans flavanol ratios ranged from 1.4/98.6 to 91.4/8.6. As a general rule, the trans flavanols, gallocatechin and catechin, were present as terminal and extension units, while most of the cis flavanols, epicatechin and epigallocatechin, occurred as extension units only. Interestingly, samples that were rich in catechin and gallocatechin as terminal units, also tended to have a high concentration of catechin and gallocatechin as extension units. The combined tannin traits caused the accessions to cluster into 2 distinct groups, which were mainly based on contrasting prodelphinidin concentrations. Gallocatechin as terminal or extension unit contributed most to this classification. The ratio of cis to trans flavanols explained the classification of subgroups. This cluster analysis reflected some of the genetic linkages, in particular for accessions that belong to the S. viminalis species. The development of this tannin trait dendrogramme will be used in the future to identify genetic markers for tannins and to lay the foundations for a future breeding programme in order to harness the benefits that willow can offer for animal nutrition and health. Tannins with contrasting structures were isolated from different willow accessions, purified and tested for their nematicidal (syn. anthelmintic) effects at INRA ENVT (UMR 1225), Toulouse, France. The anthelmintic activity was measured against the infective larvae of an abomasal species, Haemonchus contortus, which was used as a model. Anthelmintic measurements were made using the Larval Exsheatment Inhibition assay (Jackson and Hoste, 2010). Preliminary results based on multivariate analyses (Principal Component Analysis) indicate that polymer size and prodelphinidin content are tannin traits, which were most important for explaining anthelmintic activity. However, the results also confirmed a potential role of simple flavan-3-ols, such as epicatechin and epigallocatechin, for the anthelmintic properties of some animal feeds. The appointed researcher was able to confirm two of the stated project hypotheses: i) that tannins differ between genetically diverse willow accessions and ii) that contrasting tannin types give rise to different anthelmintic responses. As the researcher needed to return to his home country early, the remaining two hypotheses will need to be tested in a separate project. Once this work will be completed, it is expected to provide new targets for willow breeding and generate impact in terms of alternative willow uses. Farmers and other animal owners are likely to make more use of shrub-based fodder systems, which are sustainable, in order to cope with summer droughts and to utilise more local instead of imported feed resources. Supplementary feeding with shrub and tree leaves will offer some resilience to farmers to cope with climate change and extreme weather events.

Data: CORDIS, © European Union