Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

Poster Abstract - 4.39

DETERMINATION OF SAPONINS IN 2N GAMETE-DERIVED ALFALFA (MEDICAGO SATIVA L.) PLANTS

mariani A.*, ursino A.**, pintus B.**, odoardi M.**

*) Istituto di Ricerche sul Miglioramento Genetico delle Piante Foraggere, CNR, Perugia

**) Istituto Sperimentale per le Colture Foraggere, MiPAF, Lodi

anti-nutritional compounds, Medicago sativa L., 2n gametes

In cultivated alfalfa (Medicago sativa L. 2n = 4x = 32 ), heterosis is dependent on heterozygosity involving allelic and non-allelic gene interactions. An effective non-conventional method for maximizing heterozygosity in tetraploid cultivated alfalfa is the use of meiotic mutants producing 2n gametes. A program involving unilateral -USP- and bilateral -BSP- sexual polyploidization was undertaken to obtain tetraploid (4x) populations from diploid (2x) mutants selected for their high production of 2n pollen and 2n eggs. The plants obtained by USP and BSP are being evaluated for forage yield and fertility, along with 2x and 4x controls.

When breeding for productivity in forage species, such as alfalfa, several factors should be taken into account. One of these is the presence of secondary metabolites with anti-nutritional activity, like saponins, affecting the quality of green forage and protein concentrates. Because the diploid species which had generated tetraploid plants by USP and BSP, had shown different saponin contents, from medium to high, a study was undertaken to determine the presence and concentration of saponins in the latter plants as compared with 2x and 4x controls and with parental species. In alfalfa, saponins are described as biologically active compounds acting as anti-quality factors for feeding poultry and piglets, but they are also thought to have a protective action against microbial pathogens and pests in plants, and a hypocholesterolemic effect in man. Therefore, the purpose of specific genetic selection programs is to obtain new high-yield alfalfa varieties with low saponin contents in the aerial parts of the plants.

For saponin determination, as a first step, USP plants, BSP plants and control plants were submitted to a micro-hemolytic test to verify the presence and semi-quantitative concentration of biologically active saponins. Preliminary results from the hemolytic test on plant samples collected in autumn 2001 show differences between BSP, USP and control plants. Analysis of leaf extracts showed moderate to strong hemolysis in 4 out of 6 BSP plants, and only 3 out of 12 USP plants, while hemolytic saponins were detected in all the control plants.

The next step consists in distinguishing among the various sapogenins from plant extracts using such quantitative chemical methods as GC and GC-MS, particularly suitable for the purpose. Gas chromatographic analyses of medicagenic acid, the sapogenin most largely represented in the genus Medicago, are still in progress. They will be useful in providing chemical markers for selection among the best performing and safest genotypes to obtain new high-yield alfalfa varieties.