Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress
Giardini Naxos, Italy - 18/21 September, 2002
REPRODUCTIVE DINAMICS OF THE FACULTATIVE APOMICT HYPERICUM PERFORATUM L.
ARZENTON F.*, BÄUMLEIN H.**, MATZK F.**, BRAKE M.*, PARRINI P.*
*) Dipartimento di Agronomia Ambientale e Produzioni Vegetali, Università di Padova, Agripolis, Via Romea 16, 35020 Legnaro, Padova, Italy
**) Institut für Pflanzengenetik und Kulturpflanzenforschung (IPK), Corrensstrasse 3, D-06466 Gatersleben, Germany
apomixis, FCSS, AFLP, St. John’s wort
St. John’s wort (Hypericum perforatum L.) reproduces by facultative aposporous and pseudogamous apomixis. Commercial interests on St. John’s wort are mainly due to the significant effects of its pharmaceutical derivatives. According to a recent finding by Schempp et al. (2002, Oncogene, 21: 1242-1250) the antibiotic hyperforin inhibits the growth of tumour cells by induction of apoptosis. As a matter of fact, the increasing importance of this species makes necessary to develop cultivars with favourable agronomic traits. Because apomixis eliminates genetic segregation and enables complex traits to be fixed in a single step, any elite genotype can be converted directly into a cultivar. Thus, a deeper knowledge of the genetic aspects of the apomictic system of H. perforatum is needed for its exploitation in breeding programs. We assessed the reproductive behavior of 18 Italian ecotypes with the flow cytometric seed screen (FCSS) method using seed bulks and single seeds. All the accessions were shown to be facultatively apomictic displaying an highly variable extent of apomixis/sexuality. One of the accessions, #13 Plois d’Alpago (BL), exhibited a reduced level of parthenogenesis in aposporous embryo sacs as indicated by the high frequency of triploid BIII hybrids produced by fertilisation of unreduced eggs (overall 44% of sexuality). In the rest of the accessions it was possible to detect different sexual off-types and sources of genetic variation like balanced BII hybrids and also haploids (7%, on average) resulting from parthenogenesis of meiotic eggs. Obligate apomictic genotypes as well as twins proved to occur rarely. The high incidence of sexual events as assessed by flow cytometric estimation of the nuclear DNA content of seeds (embryo plus endosperm) was confirmed by high degree of genomic DNA polymorphisms detected among plants within ecotype using molecular markers. We found that the within H. perforatum population genetic similarity estimates ranged from 0.624 (#4 Cellarda, BL) to 0.964 (#14, Tisoi, BL) being equal to 0.849 on average and to 0.979 for the cultivar Topas adopted as reference standard. Furthermore, we analysed ten apomictic and six sexual genotypes from different accessions from Matzk et al. (2001, Plant J. 26: 275-282) using 46 Pst/Mse primer combinations in order to develop AFLP markers linked to the apomixis trait. The seven markers selected as specific of the apomictic plants will be cloned and converted into SCAR markers or used as probes for Southern analysis. The SCARs or RFLPs will be then exploited to screen an F1 population derived from a sexual by apomictic cross combination in order to: I) confirm the classification based on the FCSS analysis; II) establish the first linkage group related to apomixis in H. perforatum; III) assess whether DNA markers are correlated with apomixis as a whole or only with one of its single components (apospory or parthenogenesis).