Cytogenetics study of Garcinia mangostana L.

Abstract

Garcinia mangostana L. (mangosteen) is one of the most popular tropical fruit of Southeast Asia. It has economic potential for both local and export markets. Today, there are two types of mangosteen cultivated in Malaysia, one with normal globose fruits (common mangosteen) and the other with oblong shape fruits with slightly pointed tip, known as mesta variety. To date, data on genome size, chromosomal characterization, and genome studies of common mangosteen variety is very much lacking. For mesta variety, the data is not available yet. This study aims to determine genome size, chromosome number, ploidy level, and origin of common mangosteen and mesta through flow cytometry (FCM), chromosome counting, 18S-25S ribosomal DNA-fluorescence in situ hybridisation (rDNA-FISH), and genomic in situ hybridisation (GISH). Using FCM with Glycine max cv. Polanka (2C=2.5pg) as a standard, the genome size of common mangosteen was found to be 6.00±0.08 pg, which was significantly lower than genome size of mesta, 6.50±0.17 pg. Chromosome count revealed that the chromosome number of common mangosteen and mesta varied from 74-110 and 104-138, respectively. Based on statistical analysis, the chromosome numbers of common mangosteen was significantly lower than that of mesta. Chromosome count analysis explained the reason why mesta has a higher genome size compared to common mangosteen. The difference in genome content might also explain different fruit morphology. For ploidy level determination, rDNA-FISH performed on common mangosteen and mesta chromosomes showed four hybridisation signals thereby indicating that both are tetraploid. Phylogenetic analysis using ITS sequences demonstrated that four Garcinia species namely G. malaccensis, G. penangiana, G.celebica (syn. G. hombroniana), and G. opaca could be candidate ancestors of mangosteen. Consequently, these four species were used as probe and blocking DNA in GISH. GISH analysis performed on mangosteen chromosomes revealed that mangosteen and mesta originated from G. malaccensis. In conclusion, cytogenetics information obtained in this study were able to describe the origin of mangosteen and the evolution of its variety, mesta. Polyploidisation in G. malaccensis led to the evolution from G. malaccensis to common mangosteen and aneuploidisation in mangosteen led to the development of mesta from common mangosteen. The cytogenetics data such as genome size and chromosome number of common mangosteen and mesta obtained from the present study are useful information for further genome sequencing project.