Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress
Giardini Naxos, Italy - 18/21 September, 2002
MOLECULAR CYTOGENETICS OF VITIS VINIFERA L. AND FICUS CARICA L: LOCATION OF rDNA SEQUENCES
FALISTOCCO E., ANTONIELLI L.
Dipartimento di Biologia Vegetale e Biotecnologie Agroambientali, Borgo XX Giugno 74, 06121 Perugia, Italy
grapevine, fig, fluorescent in situ hybridization, ribosomal genes, triploidy
Grapevine (Vitis vinifera L.) and fig (Ficus carica L.) are among the oldest fruit trees cultivated in the Mediterranean regions. The thousands varieties of grapevine actually existing derive from the single species V. vinifera which originated in Mid Asia. Compared to other crops of similar importance, genetic studies in this species began only recently. Nevertheless, the molecular approach used in the last years has contributed to a very rapid increase in the knowledge of the grape genome. F. carica is very widespread species mainly because of the rusticity and the high capability of adaptation of its wild form: the caprifig. The species is usually considered gynodioecious rather than dioecious since it comprises female plants having only female flowers and plants with separate male and female flowers. These plants, althought hermaphrodite, are considered functionally male because produce pollen. Althought the species is very interesting from a biological point of view, genetic studies are very scanty, paricularly those concerning chromosomes, a situation common to many tree species of agricultural interest. The development of molecular cytogenetic techniques, such as in situ hybridization with fluorochromes (FISH), has given a tremendous impulse to chromosome studies with great benefit of species which are unsuited to conventional cytological treatments. The physical mapping of repetitive genes is often the first step to acquire information on genome structure of species almost unexplored from the cytogenetic point of view.
In this study the physical location of 18S-5.8S-25S and 5S ribosomal genes on chromosomes of V. vinifera and F. carica was analyzed by using the probes pTa71 and pXVI in double target in situ hybridization. Ten accessions of grapevine and fifteen of fig were investigated.
The chromosome numbers 2n=38 and 2n=26 were confirmed for V. vinifera and F. carica, respectively. One plant of fig resulted to be triploid with 2n=3x=39. The results of FISH revealed that in the genome of V. vinifera there are two pairs of sites of 18S-5.8S-25S genes presumedly associated to the secondary constrictions. A certain difference in the intensity of the signals of the hybrid sites was observed among accessions. Only one pair of loci of 5S genes was instead found. In all the accessions these loci appeared very small and were difficult to detect. The distribution of the rDNA sequences in F. carica was similar to that of grapevine with two pairs and one pair of 18S-5.8S-25S and 5S gene sites respectively. However in this species the 5S loci have a remarkable size and were always clearly distinguished. The results of this study is providing information on the chromosome organization of these species, in order to realize a molecular karyotype of both V. vinifera and F. carica.