Integrated genetic map of tomato chromosome 3
Evan der Blezen, A., Overduin, B., Nljkamp, H. J. J. and Hille, J.
Department of Genetics, Institute for Molecular Biological Sciences, BioCentrum Amsterdam, Vrije Universiteit, De
Boelelaan 1087, 1081 HV Amsterdam, The Netherlands
The tomato Altemaria stem canker (Asc) locus confers resistance to the fungal pathogen Alternaria
alternata f. sp. lycopersici and is linked to sf (solanifolia) on chromosome 3L (Witsenboer et al., 1989). Using
molecular markers from Tanksley et al. (1992), we recently introduced Asc on the RFLP map (will be published
elsewhere). The chromosomal position of Asc on the RFLP map, however, showed to be different from the
predicted location on the integrated map (Koornneef at al., 1993). In order to correctly place Asc on the integrated
map, three-point crosses are required. To this end, a chromosome 3 tester was selected containing the markers sy
(sunny), bls (baby lea syndrome), asc and sf from an F2 between LA 1004 and LA 1182. Subsequently, this tester-
3 was crossed to ET570 which harbors a T-DNA in a Moneymaker background. This T-DNA was localized on the
end of chromosome 3L by RFLP mapping and encodes resistance to kanamycin (Km) (K. Theres, pers. comm.).
The resulting F2 segregated for 5 loci in coupling phase: sy, bls, Asc, sf and Km. For Asc detached leaflet assays
were performed (Witsenboer et al., 1989). Km was scored following spraying with kanamycin (Weide et al., 1989).
All markers segregated in a 3:1 fashion. Recombinant fractions were calculated using JOINMAP (Stam, 1993)
(Table 1). The Asc locus mapped between bls and sf (Figure 1). Km mapped distal to sf and consequently, the
ET570 T-DNA is presently the most distal marker on the classical map of 3L.
Because Asc and ET570 now have been mapped on the classical map and the RFLP map, integration of
the maps is possible. To construct an integrated map, linkage data of different markers have been used: classical
markers (references in Koornneef et al., 1993), RFLP markers (Tanksley et al. 1992), and data combining both
classic and RFLP markers (Figure 1). In addition to the Asc and ET570 linkage analyses that combine RFLP and
classical markers, RFLP mapping data were included of sy, r and sf (Koornneef at al., 1993) and of r (Chetelat at
al., 1993). The limitation of the classical map is that the markers were not all mapped relative to each other.
Because most markers were mapped to sy and sf or to r (the backbones of the classical map), we used these to
construct the integrated map. Although pdc has only been shown to be linked to sy, the marker was incorporated
because it is the most distal marker on 3S. All recombination values and map positions were calculated using the
computer program JOINMAP (version 1.3) with a LOD score of 3.0 for linkage groups, a LOD 0.05 for mapping,
end Kosambi's mapping function (Stam, 1993). From figure 1 it is apparent that the integrated map of. the long arm
of chromosome 3 allows alignment of markers from different maps. In order to align markers on 3S, additional
classical markers (e.g. pdc, cn, sy, wf) should be linked to RFLP markers. We would like to thank K. Theres for
making available ET570 seeds and RFLP data, C. Rick for the gift of marker lines, M. Koornneef, R. Chetelat and
S. Tanksley for exchanging linkage data, and P. Stam for developing and sharing the JOINMAP computer
package.
Literature Cited:
Chetelat R.T., Klann E., DeVerna J.W. Yelle S., and Bennett A.B. (1993) Inheritance and genetic mapping of fruit
sucrose accumulation in Lycopersicon chmielewskii. Plant J 4: 643-650
Koornneef M., Bade J., Hanhart C., Horsman K., Schel J., Soppe W., Verkerk R., and label P. (1993)
Characterization and mapping of a gene controlling shoot regeneration in tomato. Plant J 3:131-141
No navigation control above? Click here!