Comparative analysis of two tomato RFLP maps

Lan, T.H., Paterson, A.H. and Wing R.A. Department of Soil and Crop Sciences, Texas A&M University, College Station, TX 77845

Comparative linkage analysis was undertaken to collate the NPI tomato RFLP map (Helentjaris at al., 1986) and a high-density tomato RFLP map developed at Cornell University which carries 1200 markers (Tanksley et al., 1992). A total of 29 molecular markers (generously provided by Pioneer Hi-Bred International, Inc., but initially prepared and described by Native Plants, Inc.) were used to probe 37 individuals from the F2 population which had been used in the construction of the high-density map (probes, plants and mapping data kindly provided by S. Tanksley, and described by Tanksley et al., 1992). Tomato nuclear DNA extraction, Southern blotting and hybridization were performed as described (Bernatzky & Tanksley, 1986). Probes were prepared by PCR amplification (Innis et al., 1990) and then labeled by the random hexamer labeling procedure (Feinberg & Vogelstein, 1984). Data were analyzed through Mapmaker (Lander et al., 1987), using the Macintosh version 1.0 (kindly provided by S. Tingey, DuPont).

Sixteen linkage groups out of 20 in the NPI tomato map have been mapped to 11 chromosomes of the Cornell high-density map (Fig 1). By mapping two or more markers per linkage group on the high-density map, the orientation of linkage groups B, G, I, J, L, M, Q, T was determined . Probes previously mapped to linkage groups F, K, L, P were found to map to loci on different chromosomes. These discrepancies probably relate to hybridization of individual probes to multiple loci in tomato. For markers 66K and 60L, each show two polymorphisms which map to different chromosomes. But since marker 59L and 60L both map to chromosome 10, linkage group L probably corresponds to chromosome 10. For linkage group F, 4F showed a single band and mapped to chromosome 2. However, 54F hybridized to multiple bands but only one was polymorphic, mapping to Chromosome 9. Because the distance between 54F and TG254 (22C) is 4.7 cM and linkage group F and C were not linked together on the NPI map, linkage group F is more likely located on chromosome 2. Finally, two probes from linkage group P mapped to three chromosomes. One of these (123P) show two polymorphisms and mapped to chromosome 7 and 8 respectively. The other (61P) mapped to chromosome 10. We have no explanation for this discrepancy.

Three water-use-efficiency associated markers, 85B, 4F and 90Q (Martin et al., 1989) map to chromosome 12, 2 and 11 respectively. Linkage groups C, D and I, carrying insect-resistance markers (Nienhuis et al., 1987), map to chromosomes 9, 6 and 1 respectively.

Figure 1. The solid bars stand for the NPI linkage groups, and the open bars represent the chromosomes in the high density map. The distance between markers was expressed as centi-Morgan in the high density map which calculated by Kosam bi mapping function and recombination frequency in the NPI map.

Chromosomes 1 and 2

Chromosomes 3 and 4

Chromosomes 6, 7 and 8

Chromosomes 9 and 10

Chromosomes 11 and 12

Acknowledgement: This study supported by Texas Agriculture Experiment Station, and USDA-NRICGP Grant #91-37300-6456 to R.A.W.

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