The negative influence of <Emphasis Type="Italic">N</Emphasis>-mediated TMV resistance on yield in tobacco: linkage drag versus pleiotropy |
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Authors: | R S Lewis L R Linger M F Wolff E A Wernsman |
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Institution: | (1) Crop Science Department, North Carolina State University, Campus Box 7620, Raleigh, NC 27695, USA;(2) 27 Parfait Lane, Alameda, CA 94502-6546, USA;(3) 436 Farmington Woods Drive, Cary, NC 27511, USA |
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Abstract: | Resistance to tobacco mosaic virus (TMV) is controlled by the single dominant gene N in Nicotiana glutinosa L. This gene has been transferred to cultivated tobacco (N. tabacum L.) by interspecific hybridization and backcrossing, but has historically been associated with reduced yields and/or quality
in flue-cured tobacco breeding materials. Past researchers have suggested the role of pleiotropy and/or linkage drag effects
in this unfavorable relationship. Introduction of the cloned N gene into a TMV-susceptible tobacco genotype (cultivar ‘K326’) via plant transformation permitted investigation of the relative
importance of these possibilities. On average, yield and cash return ($ ha−1) of 14 transgenic NN lines of K326 were significantly higher relative to an isoline of K326 carrying N introduced via interspecific hybridization and backcrossing. The negative effects of tissue culture-induced genetic variation
confounded comparisons with the TMV-susceptible cultivar, K326, however. Backcrossing the original transgenic lines to non-tissue
cultured K326 removed many of these unfavorable effects, and significantly improved their performance for yield and cash return.
Comparisons of the 14 corresponding transgenic NN backcross-derived lines with K326 indicated that linkage drag is the main factor contributing to reduced yields in TMV-resistant
flue-cured tobacco germplasm. On average, these transgenic lines outyielded the conventionally-developed TMV-resistant K326
isoline by 427 kg ha−1 (P < 0.05) and generated $1,365 ha−1 more (P < 0.05). Although transgenic tobacco cultivars are currently not commercially acceptable, breeding strategies designed to
reduce the amount of N. glutinosa chromatin linked to N may increase the likelihood of developing high-yielding TMV-resistant flue-cured tobacco cultivars. |
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