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

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Poster Abstract - 5.58

DETERMINATION OF SAPONINS AS ANTI-NUTRITIONAL COMPOUNDS IN ALFALFA (MEDICAGO SATIVA L.)

B. PINTUS*, A. TAVA*, M. ODOARDI*, A. MARIANI**

*) Istituto Sperimentale Colture Foraggere, Viale Piacenza 29, I-26900 Lodi

**) Istituto di Genetica Vegetale – Sezione di Perugia, CNR, Via Madonna Alta 130, I-06128 Perugia

Medicago sativa L., anti-nutritional compounds, saponins

In 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. Tetraploid plants were produced by unilateral (USP) and bilateral (BSP) sexual polyploidization from diploid (2x) mutants selected for their high production of 2n pollen and 2n eggs. When breeding for productivity in forage species such as alfalfa, one of several factors to be taken into account is the presence of metabolites with an anti-nutritional activity. Among these substances are saponins, because they can affect the quality of green forage and protein concentrates. Based on these considerations, a specific programme of genetic selection was undertaken to obtain new high yield alfalfa varieties with a low saponin content in the aerial parts of the plants. A number of plants obtained by USP and BSP, along with 2x and 4x controls, were evaluated for saponin content and type. A first determination was made by applying a semi-quantitative, micro-hemolytic test to verify the presence and semi-quantitative concentration of biologically active saponins. The test was performed on leaf samples harvested in autumn and spring, in order to estimate possible differences in saponin content among various plant groups and between different growth seasons.

The results of the hemolytic test showed differences among the groups of plants, as well as variations between the two growth seasons. Specifically, the frequency and level of hemolysis decreased in the BSP group from autumn to the following spring, while in the USP group the presence of strongly hemolytic individuals was confirmed. The 4x and 2x controls were only slightly hemolytic.

The next step of the research consisted in distinguishing among the various sapogenins from plant extracts by quantitative chemical methods, and in determining the content of medicagenic acid, the sapogenin most largely represented in the genus Medicago. Qualitative and quantitative analyses of derivatized sapogenins were carried out by Gas Chromatography and GC-MS. These analyses, still in progress, will allow us to define the possible utilization of medicagenic acid as a chemical marker of the selected genotypes to obtain new high yield and high quality varieties. We will also look for a possible dose effect of the saponins in the tetraploidization process as a result of the doubling of the number of alleles involved in the determination of this metabolite.