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Post by templeton on Dec 28, 2012 5:58:14 GMT -5
I've got a persistent problem with powdery mildew in tomatoes, and this season sourced a few F1 lines that so far seem to be resistant. Most of my preferred varieties seem to be susceptible. Does anyone have information on what these genes might be, and how I might go about introducing them into some of my desired varieties? The F1 resistant lines I've got are Granadero, Geronimo, Masada and Kadima - unfortunately Tropic seems to be succumbing like everything else. It would be great to get resistance into some dwarf lines as well since their growth habit seems particularly suited to promotion of the disease. Any suggestions most welcome. Would particularly like to know if these are a suite of genes, and whether they are dominant or recessive (or something else). I'll be doing some crosses anyway, but a bit of background might help me decide on strategies. T
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Post by DarJones on Dec 28, 2012 22:43:05 GMT -5
The source of Leveillula taurica resistance is the lv gene which was derived from S. Chilense accession LA0458. It appears to be recessive so you would have to grow an F1 which would be susceptible, then the F2 seedlings would segregate with 1 resistant plant and 3 susceptible.
DarJones
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Post by raymondo on Dec 28, 2012 23:21:31 GMT -5
TGRC has that gene listed as Lv, dominant. It is also referred to as such in a number of papers. Breeding is a little more problematic with a dominant gene, but not impossible. Apparently the development of resistant cultivars has been hampered by linkage drag. Early work with the resistant cultivar Laurica showed that an entire segment of chromosome 12 (where the gene lies) was of foreign origin (S. chilense) and this brought with it a host of undesirable characteristics. The segment is tightly linked so tends to move as a block, carrying with it the undesirable traits. However, that was some time back. Presumably the linkage group has been broken up with more recent work and modern resistant cultivars would be of better quality. TGRC lists two accessions that contain Lv - LA3118 (Laurica) and LA3119. Since the resistant cultivars you have T are all F1s they are probably heterozygous Lvlv. So, if you cross them into Japanese Black Trifele for example, half your F1s from the cross will be heterozygous Lvlv and presumably resistant. You would have to select these to create the F2 generation which will then be 3/4 Lv_ and 1/4 lvlv. Then the fun begins as you try to identify lines that are homozygous LvLv! There is another bug that causes PM in tomatoes, Oidium neolycopersici. It is more like the classic PM found in legumes with white powder-like deposits on leaves. There are at least two genes involved with this one (one incompletely dominant and another recessive). There is also possibly a third. Here's a flyer with a little info, though no list of cultivars: libnts.avrdc.org.tw/fulltext_pdf/FLYER/f0158.pdf
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Post by templeton on Dec 29, 2012 1:13:21 GMT -5
Thanks, gentlemen. Will get to work with the forceps. T
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Post by wildseed57 on Dec 29, 2012 12:29:33 GMT -5
Hi I have this problem here in Missouri, last year it killed over half of the tomato plants I grew the rest was killed out by blight and spider mites, so if anyone finds a variety that would make a good tomato other than some tiny current or cherry type and is indeterminate please let me know. I'm hoping Tom might release something that would work in my dry but very humid conditions here in missouri.
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Post by templeton on Dec 29, 2012 16:42:32 GMT -5
wildseed, I'll keep people posted on how my varieties go. there are a number of sources of seed in north america, have a look at Johnnys catalog - but these hybrids aren't cheap. T
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Post by wildseed57 on Jan 1, 2013 16:24:15 GMT -5
Thanks Templeton, I know that they are not cheap else wise the breeders wouldn't get anything for their hard work. Most of the work here in the states is on blight resistant varieties and some on nematodes, Missouri seems to be the worst for mildew compared to the Pacific North west Coast and East Coast areas where the weather is wetter and cooler, but not as hot and humid as the Midwest is getting.
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