The dominant nature of this Sw-5 gene is particularly useful to select
resistant heterozygous/homozygous plants from a hybrid such as Bolseno. Fully 3/4 of the F-2's will be resistant, and logically 1/4 will be not. Only one third of the resistant plants will be homozygous and true breeding. The other 2/3 will segregate again for the 1:2:1
An inoculation test with a TSWV virus strain also may be performed
to confirm the successful introgression of resistance in breeding lines. Who does this service?
One of the reasons I have made a number of crosses with Sophya, is that in addition to the intermediate resistance to TSWV, it carries resistances to
Fusarium crown & root rot
Fusarium wilt 1 and 2
Root knot
Gray leaf spot
Tomato mosaic
Tomato yellow leaf curl
Verticillium wilt
and is a rare indeterminate line.
Therefore, half of the crosses to other lines will carry a heterozygous gene. Furthermore, half of those crosses to yet other lines will 1:1 hit or miss. That is OK since look at all the other traits that may pull through.
I put these crosses away and may send them out to areas where TSWV is a problem. If the heirloom quality of the tomatoes meet acceptance AND is resistant to TSWV, I must have great numbers of crosses and segregating selfed lines to obtain even a modicum of cool lines.
Tom Wagner
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