A new citrus linkage map based on SRAP, SSR, ISSR, POGP, RGA and RAPD markers

Sequence-related amplified polymorphism (SRAP), simple sequence repeats (SSR), inter-simple sequence repeat (ISSR), peroxidase gene polymorphism (POGP), resistant gene analog (RGA), randomly amplified polymorphic DNA (RAPD), and a morphological marker, Alternaria brown spot resistance gene of citrus named as Cabsr caused by (Alternaria alternata f. sp. Citri) were used to establish genetic linkage map of citrus using a population of 164 F-1 individuals derived between 'Clementine' mandarin (Citrus reticulata Blanco 'Clementine) and 'Orlando' tangelo' (C. paradisi Macf. 'Duncan' x C. reticulata Blanco 'Dancy'). A total of 609 markers, including 385 SRAP, 97 RAPD, 95 SSR, 18 ISSR, 12 POGP, and 2 RGA markers were used in linkage analysis. The 'Clementine' linkage map has 215 markers, comprising 144 testcross and 71 intercross markers placed in nine linkage groups. The 'Clementine' linkage map covered 858 cM with and average map distance of 3.5 cM between adjacent markers. The 'Orlando' linkage map has 189 markers, comprising 126 testcross and 61 intercross markers placed in nine linkage groups. The 'Orlando' linkage map covered 886 cM with an average map distance of 3.9 cM between adjacent markers. Segregation ratios for Cabsr were not significantly different from 1:1, suggesting that this trait is controlled by a single locus. This locus was placed in 'Orlando' linkage group 1. The new map has an improved distribution of markers along the linkage groups with fewer gaps. Combining different marker systems in linkage mapping studies may give better genome coverage due to their chromosomal target site differences, therefore fewer gaps in linkage groups.