Comparison of linkage maps from F2 and three times intermated generations in two populations of European flint maize (Zea mays L.).

Intermated mapping populations are expected to result in high mapping resolution for tightly linked loci. The objectives of our study were to (1) investigate the consequences of constructing linkage maps from intermated populations using mapping methods developed for F(2) populations, (2) compare linkage maps constructed from intermated populations (F(2)Syn3) with maps generated from corresponding F(2) and F(3) base populations, and (3) investigate the advantages of intermated mapping populations for applications in plant breeding programs. We constructed linkage maps for two European flint maize populations (A x B, C x D) by mapping 105 SSR markers in generations F(2) and F(2)Syn3 of population A x B, and 102 SSR markers in generations F(3) and F(2)Syn3 of population C x D. Maps for F(2)Syn3 were constructed with mapping methods for F(2) populations (Map A) as well as with those specifically developed for intermated populations (Map B). Both methods relate map distances to recombination frequencies in a single meiosis and, therefore, did not show a map expansion in F(2)Syn3 compared with maps constructed from the respective F(2) or F(3) base populations. Map A and B differed considerably, presumably because of theoretical shortcomings of Map A. Since loosely linked markers could not unambiguously be mapped in the F(2)Syn3 populations, they may hamper the construction of linkage maps from intermated populations.

Molecular mapping of the Rf1 gene restoring pollen fertility in PET1-based F1 hybrids in sunflower (Helianthus annuus L.).

Up to now a single cytoplasmic male sterility (CMS) source, PET1, is used worldwide for hybrid breeding in sunflower. Introgression of the restorer gene Rf1, responsible for fertility restoration, into new breeding material requires tightly linked markers to perform an efficient marker-assisted selection. A survey of 520 decamer primers by bulked segregant analyses identified five RAPD markers linked to the restorer gene Rf1. In a F(2) population of 183 individuals one of the RAPD markers, OPK13_454, mapped 0.8 cM from Rf1, followed by OPY10_740 with 2 cM. Bulked segregant analyses using 48 AFLP primer combinations identified 17 polymorphisms, which could be mapped in the same linkage group as Rf1. E33M61_136, and E41M48_113 were mapped 0.3 cM and 1.6 cM from the gene, respectively. Conversion of E41M48_113 into a sequence-specific marker resulted in a monomorphic pattern. However, two of the RAPD markers, OPK13_454 and OPY10_740, were successfully converted into SCAR markers, HRG01 and HRG02, which are now available for marker-assisted selection. To investigate the utility of these SCAR markers in other cross-combinations they were tested in a set of 20 lines. Comparison of the patterns of 11 restorer and nine maintainer lines of PET1 demonstrated that the markers OPK13_454/HRG01 and HRG02 were absent in all maintainer lines but present in all restorer lines, apart from the high oleic line RHA348 and the dwarf line Gio55. In addition, restorer lines developed from the interspecific hybrids Helianthus annuus x Helianthus mollis and H. annuus x Helianthus rigidus gave the same characteristic amplification products.