I have found this a hard subject to make simple. But here goes...

Tomato late blight resistance genes are non-allelic

Quote:
Non-allelic genes are genes located at different loci on the same
chromosome or on different chromosomes altogether.


The gene, Ph-3, Chromosome 9
Ph-1 (chromosome 7
Ph-2 (chromosome 10).

Reports are that
Quote:
WV106
carried a single dominant allele conditioning a high level
of resistance to P. infestans tomato race 0 (T0)
(Ph-1)

and that WV700 possessed one or more dominant resistance genes (but is associated with Ph-2)


Quote:
Researchers at the AVRDC identified resistance to late blight from Solanum pimpinellifolium L. accession L3708. Segregation data obtained for resistance do not support the hypothesis of single gene control of the full resistance trait, but suggest that more than one gene is involved, and that these genes interact in an epistatic manner. Differential responses were also observed between the resistant CU-R lines and the resistant CLN-R lines, which were independently bred from L3708. RFLP analysis confirmed the Ph-3 gene derived from L3708 is located on chromosome 9.



The meaning of (genes interact in an epistatic manner )
epistatic (not comparable)

1. (genetics) Of or pertaining to epistasis, the interaction between genes.

I have a lot of self doubt about my work with Late Blight resistance. Since I had great results with sinlgle dominance with WV 700 with my particular strain of it for years 2004-2007. But 2008 is a year that needed homozygous Ph-2 and Ph-3 clones. Mountain Magic has heterozygous genes as a hybrid and it did not survive to the end of the infestation process. Only my most homozygous clone (Ph-2 and Ph-3)survived totally. I will be testing some seedlings from the recent hybrid of WV 700 X homozygous Ph-1 and 2 for this fall. The hybrid would be homozygous for Ph-2 but only heterozygous for Ph-1.


The good news is that I am transferring the genes Ph-2 and Ph-2 into a wide variety of clones such as Black Pineapple, Black Prince, Green Sleeves, WV 700, and many, many more. I've got to remind myself to sow a huge compilation of varieties soon.

The kind of work I am doing with require that I do a large extension collaboration. I will be exploring ideas to that effect soon.

Tom Wagner