Cytological variation of rRNA genes and subtelomeric repeat sequences in Indonesian and Japanese cucumber accessions

抄録

Genomic study is very important for understanding function of chromosomes, delving into evolution, and providing useful information for the strategies of genome manipulation. Karyotyping using Fluorescence in situ Hybridization (FISH) technique is one of the ways to achieve these goals. Although many publications describing cucumber chromosome analyses have been appeared, information on Indonesian cucumber is still rare. In the present study, karyotypes of four Indonesian pureline cultivars, five Indonesian hybrid cultivars and two landrace varieties of Japanese cucumber were observed and compared. Repetitive sequences of 45S and 5S rDNAs and one type of tandem repetitive DNA sequence (type I) were hybridized as FISH probes to mitotic chromosomes of cucumber. The results showed variation in the numbers of 45S rDNA signals, especially in the Indonesian hybrid cultivars which had the most various numbers of signals (eight, nine, and ten signals) among the accessions studied. Two Indonesian hybrid cultivars and one Japanese landrace variety had unpaired signals of 45S rDNA. On the contrary, all accessions had same number of 5S rDNA signals (a pair signals) on chromosome 5. The type I signals distributed on all of the cucumber chromosomes either at one end of the chromosome arm or at both ends of the arms in almost of all cucumber accessions. However, three accessions of Indonesian cucumber did not have type I signals on one of their chromosomes (i.e., chromosome 7). The data showed that Indonesian cucumbers investigated here had different karyotypes from the previous reports, implying potential genetic variation in Indonesian varieties.