Inter-simple Sequence Repeat Fragments Research Articles

Phylogenetic Relationships among Selected Citrus Germplasm Accessions Revealed by Inter-simple Sequence Repeat (ISSR) Markers

ISSR markers were analyzed to study phylogenetic relationships among 46 Citrus L. accessions representing 35 species. A dendrogram based on the unweighted pair-group method, arithmetic average cluster analysis was constructed using a similarity matrix derived from 642 polymorphic ISSR fragments generated by 10 primers. These 46 accessions could be classified into five major groups: 1) C. indica Tan.; 2) C. maxima (Burm.) Merrill; 3) lemon [C. limon (L.) Burm.] or lime [C. aurantifolia (Christm.) Swingle] type accessions; 4) C. halimii B. C. Stone; and 5) sour orange (C. aurantium L.), mandarins and their hybrids. Group 5 was further divided into three subgroups. Although some previous work had grouped it with mandarins, C. indica appeared to be a distinct genotype or species that was not close to mandarins. C. tachibana Tan. grouped closely to mandarins. C. vulgaris Risso was not related to sour orange but was similar to accessions usually classified in the lime or lemon group. Sour orange and its hybrids, C. nippokoreana Tan., C. hanayu Hort. ex Shirai, C. sudachi Hort. ex Shirai, and C. yuko Hort. ex Tan. had close phylogenetic relationships with mandarins. Although the mandarin accessions studied were divergent in morphology, the genetic distances among them were relatively small. Relationships among these Citrus accessions revealed by ISSR markers were generally in agreement with previous taxonomic classifications.

Genetic linkage map of ISSR and RAPD markers in Einkorn wheat in relation to that of RFLP markers

The potential of PCR-based markers for construction of a genetic linkage map in Einkorn wheat was investigated. From a comparison of polymorphisms between two Einkorn wheats, Triticum monococcum (Mn) and T. boeoticum (Bt), we obtained 49 polymorphic bands produced by 33 primers for inter-simple sequence repeat (ISSR) and 36 polymorphic bands shown by 25 combinations of random amplified polymorphic DNA (RAPD) primers for mapping in 66 individuals in the F2 population. Although 44 ISSR fragments and 29 RAPD fragments statistically showed a 3 : 1 segregation ratio in the F2 population, only 9 markers each of the ISSR and RAPD bands were able to be mapped on the RFLP linkage map of Einkorn wheat. ISSR markers were distributed throughout the chromosomes. The mapped positions of the ISSR markers seemed to be similar to those obtained by the RFLP markers. On the other hand, 4 of the 9 RAPD markers could map the RFLP marker-poor region on the short arm of 3Am, suggesting a potential to map novel regions containing repetitive sequences. Comparisons of the genetic linkage map of Einkorn wheat to the linkage map and cytological map of common wheat revealed that the marker orders between the two maps of Einkorn wheat and common wheat coincided except for 4A, which harbors chromosome rearrangements specific for polyploid wheats, indicating a conservatism between the two genomes. Recombinations in Einkorn wheat chromosomes took place more frequently around the centromere and less at the distal part of chromosomes in comparison to those in common wheat. Nevertheless, recombinations even in Einkorn wheat chromosomes were strongly suppressed around the centromere. In fact, the markers located within 1 cM of the centromere were located almost in the central part of the chromosome arm.