Map location Diaphorase-3 (Dia-3),a new isozyme marker on 9S.

Chetelat, R.T., Takahashi, M. and DeVerna*, J.W. Dept. of Vegetable Crops, Univ. of California, Davis, CA 95616
* Campbell Soup Research and Development, 28605 County Rd. 104, Davis, CA 95616

The diaphorase isozymes are well resolved on starch gels using a Tris-citrate/sodium-borate pH 7.8 system and the MTT/DCPIP activity detection method (Wendel and Weeden 1989). Both shoots and roots are satisfactory sources of the enzyme. Analysis of a set of S. lycopersicoides alien addition lines (DeVerna et al. 1987) indicated at least three loci on separate chromosomes are responsible for the array of bands produced: Dia-1 on chromosome 5, Dia-2 on chromosome 1, and Dia-3 on chromosome 9. The Dia-3^1^ band from S. lycopersicoides is slightly retarded relative to Dia-2+, both of which are advanced relative to Dia-1. Under our conditions, no corresponding Dia-3+ band was detected in L. esculentum, which may be null for the locus. Accordingly, Dia-3^1^ is scored as a dominant. For the present linkage study, a BC3F2 plant carrying the marker was identified among diploid derivatives of S. lycopersicoides (Chetelat et al. 1989) and was crossed to the chromosome 9 linkage tester stock LA1001 containing the markers ah and marm. The results of the test cross (Table 1) indicate significant associations between Dia-3 and ah (X^2 = 97.2) and between ah and marm (X^2 =5.17), but not between Dia-3 and marm (X^2 = 3.6). The data indicate Dia-3 is not in between ah and marm, hence is most likely on 9S, given the proximity of ah to the centromere. The following map illustrates these relationships:

The map position of Dia-3 is being further refined by linkage studies with pct, a new marker on 9S (Rick et al. 1992), as well as the isozyme locus Est-2.

Table 1. Frequency of genotypes from the repulsion test cross of Dia-3^1^ x ah - marm.

__________________________  __________________________
# Plants  Dia-3  ah  marm   # Plants  Dia-3  ah  marm
__________________________  __________________________
  82        1     +   +       73        1     +  marm
  52       null  ah  marm     56       null  ah   +
  31        1    ah  marm     11        1    ah   +
  27       null   +   +        9       null   +  marm
__________________________  __________________________

Literature cited

Chetelat, R.T., DeVerna, J.W. and Rick, C.M. (1989) Genome 32: 783-790.

DeVerna, J.W., Chetelat, R.T. and Rick, C.M. (1987) Biol. Zent. bl. 106: 417-428.

Rick, C.M., Baergen. K., Chmielewska, W., Tarquis, A.M. and Chetelat, R.T. (1992) TGC 42: 31-32.

Wendel, J.F. and Weeden, N.F. (1989) In: Soltis, D.E. and Soltis, P.S. (eds) Isozymes in Plant Biology, Dioscorides Press, pp5-45.