Genetic diversity in sesame (Sesamum indicum L.): molecular markers, metabolic profiles and effect of plant extracts on soil-borne pathogenic fungi | Genetische Diversität in Sesam (Sesamum indicum L.): Genomebene, Profile der Sekundärmetabolitenproduktion und Wirkung von Sesam-Extracten auf mikrobielle Krankheitserreger

Zusammenfassung

Sesame (Sesamum indicum L.) is an important crop in tropical and subtropical areas. Sesame seed is traditionally used for direct consumption, because of its high nutritional value (50 % oil and 25 % protein), and as a source of oil of excellent quality. Potentially beneficial effects of sesame on human health have recently renewed the interest in this ancient crop. Information on the genetic diversity in sesame is limited, only some studies about morphological diversity have been carried out, and generally, these studies have been focused on regional interest. To overcome this gap of knowledge in sesame, this research was achieved to know how diverse is a sesame germplasm collection containing both accessions from different origin regions, and commercial cultivars or experimental lines. Genetic diversity was assessed at three different levels: DNA (by means of amplified fragment length polymorphism or AFLP), metabolic profiles, and functional metabolites (by means of effect of plant extracts on soil-borne pathogenic fungi). Individual outputs for every approach were obtained, but also information about usefulness of AFLP for identifying sesame cultivars, optimal conditions for bioassays, and identification of sesame accessions potentially valuables for breeding and/or production of natural compounds against soil-borne fungi The assessment by means of AFLP resulted in a high level of variability within all diversity centres except Central Asia. No association between geographic origin and AFLP patterns was found. Most of the variation is explained by genetic diversity within origin regions rather than between origin regions. According to the results, conservation strategies do not need to cover all diversity centres as long as they sample a sufficient number of accessions. Similarly, choosing parent genotypes for breeding programs from many diversity centres as compared to sampling just one centre (except Central Asia) is not likely to increase the variability among progeny significantly, whether the objective is breeding for poligenic traits such as yield. AFLP-based fingerprints demonstrated to be useful for identifying unequivocally sesame genotypes, resulting an average and maximum probability of identical match by chance between 2 accessions of 2.7 x 10-7 and 5.2 x 10-5 respectively. Correlation between AFLP and metabolic profiles was not found, but some important consistencies were reported. Metabolic profiles were obtained from seeds; and indirect selection on some metabolites at seed by farmers and differences in the sampling on the genome of the two methodologies could explain the results. Identification of similarity/dissimilarity relationship between pairs, based on AFLP and seed metabolic profiles, depend on the genotypes under comparison, due to differences in evolutionary history of each genotype. Therefore the assumption that genetic distance between two genotypes is directly proportional to the probability of identifying very different levels in some important agronomic or quality trait is not necessarily true, and is not supported by this work. Search in plants of novel compounds with antimicrobial properties requires large screening of accessions, not only at inter-species level, but also within species. Adequate system of screening must be available for this goal. The present study report the standardization of a biosassay to test biological activity of novel compounds on growth of Macrophomina phaseolina. The proposed bioassay has the advantage of being suitable to test small amount of compounds, reducing required laboratory space and therefore being suitable for testing a great amount of sources with several replications. This is especially advantageous for testing natural compounds from plant genetic resources collections, because of the large amount of sources available. The present study shows the importance of large screening within a species when antifungal activity from plants are being searched. Large within-species genetic variation has been originated by evolutionary forces, which can lead to differentiation at metabolite level and therefore, in the effect of plant extracts on fungi growth. Extreme response of fungi before plant extracts from different accessions of sesame are reported in this study: large stimulatory effect or strong growth inhibition. Some accessions have been identified as potentially valuable for breeding and/or production of natural products to control soil-borne fungi, not only from root extracts, also from stem, leaf and seed extracts. Results of the present study suggest that toxic compounds to fungi are present in all the accessions, but final effect on fungi growth depend on its balance respect to other compounds present in the plant organ.