Volume 60 - Tomato Genetics Cooperative - University of Florida

The average DSI for RS families with the T1-Ty3 introgression was 1.7 while
DSI for those SR families with the Ty2 introgression was 4.8. RR families with both
introgressions for resistance had an average DSI of 1.4 and those with neither
introgression had DSI of 3.6. There was no difference in the average DSI for the RR
and SR families. Surprisingly, the DSI for the SR families was higher than the DSI for
the SS families. These observations indicated that Ty2 introgression provides no
effective resistance to these begomoviruses.
An important observation was that there was a considerable range in the
average DSI for families with the same genotype for these two introgressions (Fig. 5).
For example, one RR family had a DSI of 3.2, which was greater than the other four
RR families (range of 0.3 to 1.4). Within the RS families, one family had a DSI of 0.2
and another RS family had a DSI of 3.8. The genotype for the markers in these
families, i.e., the presence or absence of the PCR fragments corresponding to the S.
lycopersicum size or the introgression size, was reconfirmed by additional testing in
the laboratory. Explanations to consider are that there could have been a
recombination event between the PCR marker and the resistance gene for these
introgressions or that other genes controlling resistance were segregating within the
F2 plants.
DSI
6
5
4
3
2
1
0
-1
F3 Families and Parents
Fig. 5. Average disease severity index (DSI) and standard errors for individual F3
families for each genotype and the two parents. See Fig. 3 for codes.
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