SCREENING SERICEA-LESPEDEZA GERMPLASM FOR HERBAGE QUALITY

Sericea lespedeza [Lespedeza cuneata (Dumont) G. Don] is recognized as being a relatively poor quality forage because of high concentrations of tannins in its leaves. Therefore, an accurate assessment of tannins in the leaves is essential for the selection of low tannin lines. The objectives of our research were to investigate improved methods of tannin analysis for the screening of the lespedeza germplasm, and to determine the relationship between in vitro dry matter digestibility (IVDMD), crude protein (CP), and leaf tannins. Field experiments containing 81 lespedeza entries were established at two locations. Herbage samples were harvested twice during the growing season for 2 yr and the leaves analyzed for IVDMD, CP, and tannin concentration by near infrared reflectance spectroscopy (NIRS). Results of an HCl-vanillin analysis of aqueous acetone extracts of fresh-frozen samples (ACE-FF) and oven-dried samples (ACE-OD), and methanolic extracts of oven-dried samples (MET-OD) were used to derive the NIRS tannin equations. Standard errors of calibration (SEC) were lowest for the MET-OD data and highest for the ACE-FF data. However, coefficients of variation (CV) were inversely proportional to SEC. Coefficients of variation of field experiments were also lowest when samples were analyzed by the NIRS tannin equation derived from ACE-FF data. Differences in tannin concentration, CP, and IVDMD existed among entries, locations, and seasons. Differences between locations and seasons were due to changes in moisture and temperature. Strong negative correlations were found for the ACE-FF tannin data and IVDMD (r = -0.90 to -0.92), and ACE-FF data and CP (r = -0.66 to -0.70) relationships. Our results indicate that the tannin analysis of ACE-FF is a better reference method for NIRS calibration and subsequent screening of the lespedeza germplasm, and that the relationships between tannins, CP and IVDMD, suggest that a significant improvement in herbage quality may be achieved.