Genetic variation in the Sicilian endangered populations of Brassica rupestris.

Abstract

Boll. Mus. Ist. Biol. Univ. Genova, 73, 2011 106° Congresso Società Botanica Italiana – Genova 21-23 settembre 2011 163 GENETIC VARIATION IN THE SICILIAN ENDANGERED BRASSICA RUPESTRIS F.M. RAIMONDO1, A. SCIALABBA1, G. ZECCA2, F. GRASSI2, G. CASAZZA3, L. MINUTO3 1 Department of Environment Biology and Biodiversity, University of Palermo, Via Archirafi 38, I-90123 Palermo, Italy. raimondo@unipa.it; germas@unipa.it; 2 Botanical Garden, Department of Biology, Università di Milano, Via Celoria 26, 20133 Milano, Italy. giovanni.zecca@gmail.com; fabrizio.grassi@guest.unimi.it; 3Department for the Study of Territory and its Resources, University of Genova, Corso Dogali 1M, I-16136 Genova, Italy. gabriele.casazza@unige.it; minuto@dipteris.unige.it Brassica rupestris Raf. is an endemic plant belonging to the Brassica section. It grows in rocky places and cliffs of the Central-Western Sicily (Italy). Rare and endangered species are susceptible to loss of genetic variation through genetic drift in small populations. Management decisions for the conservation of rare taxa necessitate an understanding of their biology and other factors, including genetic variability. For this reason the gathering of data on population genetic structure of rare species has become a common prelude to their conservation planning (Ellstrand & Elam, 1993). In the present study the ISSR technique was used to examine natural populations of B. rupestris (both subsp. rupestris and subsp. hispida) for the following purposes: 1) to evaluate the genetic diversity both at species and subspecies levels, 2) to assess the genetic differentiation of populations and 3) to provide suggestions for effective conservation programs. Six natural populations of B. rupestris subsp. rupestris and two populations of B. rupestris subsp. hispida, covering the whole range of the two subtaxa, were investigated and mapped using GPS (Garmin) in order to evaluate their genetic diversity. Six were from Palermo province: S. Calogero, Capo Zafferano, P.so Scuro - Castelbuono, Mt. Pellegrino, Mt. Kumeta, Mt. Pizzuta; one from Agrigento province: Gole Tardara - Sciacca; one from Reggio Calabria province: Stilo. ISSR were used to detect the genetic diversity within and among populations representative of the species distribution range. From each site, a variable number (8< N <10) according to the availability of individuals were randomly sampled (n = 76); 1-2 leaves per plant were dried in situ in silica gel, washed in laboratory and total genomic DNA extracted by using DNeasy Plant Mini Kit (Qiagen) following the manufacturer‘s instructions. High levels of genetic diversity were revealed both at population (PPB = 53.88%, HS = 0.2115, Sh = 0.3085) and at species level (PPB = 96.55%, HT = 0.3070, Sh = 0.4638). The correlation between genetic and geographic distances was negative (Mantel test, r = -0.23). Our data on B. rupestris revealed that about 67% of genetic variation is detectable within the population while 23% among populations within infraspecific taxa. This fact is also confirmed by the quite good value of migration rate among populations and it could be explained by hypothesizing the self-incompatibility systems, often found in many Brassica populations (Geraci et al., 2004). The information on the pattern of genetic variation obtained in the present work bear important inferences for conservation management, and in particular for ex situ conservation programmes. The populations showing local markers (Gole Tardara, San Calogero, and Mt. Pellegrino) deserve particular attention for their important presence in a seeds bank. This research was supported by PRIN 2007JNJ7MX_003 project. Ellstrand C. & Elam D.R., 1993. Population genetic consequences of small population size: implications for plant conservation. Annu Rev Ecol Syst 24:217–242. Geraci A., Chèvre A.M., Divaret I., Eber F. & Raimondo FM., 2004. Isozyme analysis of geneti