New evidence for placement of Ve - the gene for resistance to Verticillium race 1.

Zamir, D., Bolkan, H., Juvik, J.A., Watterson, J.C. and Tanksley, S.D. Department of Plant Breeding, Cornell University, Ithaca, NY 14853

A single dominant gene, Ve, for resistance to Verticillium wilt race 1 was identified in 1932 in a Peruvian accession; the first resistant varieties were released in 1952 (Stevens and Rick 1986). The gene was first reported to reside on chromosome 12 (Kerr and Busch 1977) and more recently on chromosome 7 (Juvik et al. 1991). The later report was based on analysis of an F5 recombinant inbred population derived from a cross between UC204B as the source of the resistance, and L. cheesmanii (LA483) a susceptible parent. Seed of 98 RI lines were evaluated for Verticillium race 1 resistance and the segregation of 96 RFLP markers. Strong association of TG20 with the resistance response was detected.

In an attempt to obtain finer mapping of Ve, 84 lines of the same RI population in a more advanced generation (F9) were inoculated. While the genotype of some of the lines was not clear, unequivocal characterization of the disease response as either homozygous resistant (Ve/Ve) or homozygous susceptible (ve/ve) was obtained for 58 lines. Our inability to characterize the entire population may be due to residual heterozygosity in the RI population (Zamir, unpub.) and possible other Ve modifier genes that segregated in the population. Association between 135 RFLP markers and the disease response was evaluated using a Chi- square test (Table 1). The results indicate that TG105B (chromosome 9; Tanksley et al. 1992) shows strong linkage with the resistance gene while the association with TG20 with Ve is no longer significant.

Markers in the TG105B region of chromosome 9 had not been tested in the earlier generation. We therefore probed DNA of F5 with TG105; the results are consistent with the effects in the F9 generation. In contrast to the F9, TG20 shows a significant association with the Verticillium response. It should be noted that TG105 is a duplicated clone in the tomato genome; TG105A is tightly linked to the gene for resistance to Fusarium race 2 on chromosome 11 (Sarfatti et al. 1989).

The preliminary results presented here suggest that Ve is located on chromosome 9 and not on chromosome 7 as originally reported, although we can not eliminate the possibility that other genetic modifiers are located elsewhere in the genome. Additional studies are in progress aimed at verifying the location of the Ve gene using different populations.

Table 1. A Chi-square independence test for the associations between RFLP markers and the Verticillium disease response in F9 and F5 recombinant inbred (RI) populations.

___________________________________________________________________________
                Resistant (Ve/Ve)   Susceptible (ve/ve)
             __________________     ___________________ 
Marker       1*      2       3      1      2       3        X^2        P
___________________________________________________________________________
RI in F9
_________
TG105B       20      2       1      8      5      22       24.1      <0.005
TG20          9      4      10     15      8      12        0.6      0.9-0.5

RI in F5 
_________
TG105B        4      0       0      2      2      11       11.0      <0.005 
TG20          7      0       3      6      4      16        7.3    0.05-0.025
____________________________________________________________________
* For each of the assayed markers, 1= homozygous for the L. esculentum alleles;
2=heterozygous; 3=homozygous for the L. chesmanii alleles.

Literature cited:

Juvik, J.A., Bolkan, H. and S.D. Tanksley (1991)Tomato Genetics Cooperative 41:23- 25
Kerr, E.A., and L.V. Bush (1977) Tomato Genetics Cooperative 27:18
Sarfatti M. et al. (1989) Theor. Appl. Genet. 78:755-759.
Stevens, M.A. and C.M. Rick (1986) Genetics and Breeding. in: The Tomato Crop. eds, J.G. Atherton and J. Rudich. Chapman and Hall pp.35-109.
Tanksley, S.D. et al. (1992) Genetics: 1141-1160.