The Inheritance of Resistance to Tobacco Mosaic Virus in Tobacco Introductions
Beekwilder, Kristen M.
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Thirty-one tobacco introductions that were reported to display either a local lesion or a symptomless reaction to infection with tobacco mosaic virus (TMV) were screened for reaction to the virus (Chaplin and Gooding, 1969). Ten tobacco introductions (TI), TI 203, TI 407, TI 438, TI 450, TI 692, TI 1203, TI 1459, TI 1462, TI 1467, and TI 1500 were randomly chosen for further study to characterize their resistance to tobacco mosaic virus (TMV). Each TI line was crossed with susceptible cultivar K 326 to determine the mode of inheritance of resistance to TMV. The F2 progeny of TIs 1459, 1462, and 1500 segregated in a 3 local lesion:1 mosaic ratio, indicating that the gene governing resistance in these three TI lines was a single, dominant trait. The F2 progeny of TIs 203, 407, 438, 450, 692, 1203, and 1467 failed to segregate, only mosaic plants were observed. This would indicate that the gene(s) controlling resistance to TMV in these lines would not provide resistance for plant breeders to incorporate into a breeding program. Each TI line was also crossed with local lesion cultivar NC 567, which contains the N gene, in order to determine if the gene(s) governing resistance in the TI lines was allelic to the N gene in NC 567. The F2 progeny of TIs 1459 and 1462 did not segregate. All progeny displayed the local lesion reaction to TMV indicating that the gene governing resistance in these two lines is allelic to the N gene. The F2 progeny of the cross between TI 1500 and NC 567 segregated in a 15 local lesion: 1 mosaic ratio, which indicates that the gene controlling resistance in TI 1500 is not allelic to the N gene. When crossed with NC 567, the F2 progeny of TIs 407, 438 and 1467, segregated in a 3 local lesion: 1 mosaic ratio. No symptomless plants were observed. There was also segregation in the F2 progeny of the crosses between NC 567 and TIs 203, 450, 692, and 1203. However, the segregation was in no discernible ratio. Once again the F2 progeny of the crosses either displayed a local lesion or mosaic reaction and no symptomless progeny were observed. This would again indicate that the symptomless TI lines do no provide heritable resistance to TMV and therefore are not acceptable as an alternative source of resistance to TMV for the plant breeder. Tobacco introduction 1500 should be investigated further because a single, dominant trait that is not allelic to the N gene governs resistance to TMV in this line.
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