Originally Posted by Fusion_power
Mountain Merit is an effort to get a larger fruited highly disease tolerant tomato out of the existing NC breeding lines. It has genes ph2, ph3, mi, sw5, i, i2, i3, ve, and sp. The problem is that some of these genes are located so close together that there have been difficulties getting them onto the same chromosome. Ph3 and Sw5 in particular were a problem. Mountain Merit has the above genes but many of them are in heterozygous state meaning that any crosses will segregate and efforts to combine the traits into a stable line will be unsuccessful.
Here are the genetics of the two lines:
NC123S - mi, i, i2, i3, ve, sw5
NC1 Celebr - i, i2, ve, ebr, ph2, ph3
As you can see, Mountain Merit is homozygous for i, i2, and ve and will segregate for ph2, ph3, sw5, and mi.
I talked to Randy Gardener 3 weeks ago about a line that was developed in Ohio that finally managed to get sw5 and ph3 onto the same chromosome. He does not have it but said he would inquire if he could get a sample. To give you an idea how difficult this is, 1152 plants were grown and 3 of them turned out to have desirable traits including homozygous sw5 and ph3.
Does this mean you shouldn't try a few crosses? No, but it means you will be working against long odds. I would suggest getting some seed of Iron Lady which contains 2 genes for septoria tolerance. Between Mountain Merit and Iron Lady you would have most of the major diseases and pests covered with the exception of Bacterial Spot.
For some more information on tomatoes and disease tolerance, you might read from links in the Winter Reading thread. Of particular interest is the Ashrafi article from Penn State about breeding for early blight tolerance. There is a variety available from TGRC that has sw7 which is a new gene for spotted wilt tolerance and there is info about mi9 which conveys nematode tolerance that does not break down at high temps. Interestingly, sw7 does not seem to be a true disease tolerance gene, rather, it seems to work by making insects avoid the plants that have the gene.
If you are interested in some partially advanced breeding stock, I have F2 seed from a cross of my Big Beef X Eva Purple Ball which Randy Gardner crossed with a disease tolerant red selection. I have not verified the genetics, but it probably has ph2, ph3, and a couple of early blight tolerance genes.
The Big Beef X Eva Purple Ball line is unique in conveying significantly increased fruitfulness. Doubling the crop is typical of the line. To my knowledge, there is no other line available that has this unique ability.
I am working with some lines that I hope will combine a few more genes to the above list. I don't want sp (determinate) so I am going to exclude it. I do want j1 (jointless) and I want to add in some genes for septoria tolerance. I also want to increase the sweetness and total flavor so I am adding in the sucr gene and will be breeding from some very high flavor heirloom lines.
DarJones
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