The negative influence of N-mediated TMV resistance on yield in tobacco: linkage drag versus pleiotropy.
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.
Lewis
R S
RS
Crop Science Department, North Carolina State University, Campus Box 7620, Raleigh, NC 27695, USA. ramsey_lewis@ncsu.edu
Linger
L R
LR
Wolff
M F
MF
Wernsman
E A
EA
D003001:Cloning, Molecular; D008040:Genetic Linkage; D007113:Immunity, Innate / Q000235:genetics; D007178:Inbreeding; D016254:Mutagenesis, Insertional; D010935:Plant Diseases / Q000235:genetics / Q000821:virology; D010940:Plant Proteins / Q000235:genetics* / Q000502:physiology; D030821:Plants, Genetically Modified / Q000502:physiology / Q000821:virology; D014026:Nicotiana / Q000235:genetics* / Q000502:physiology / Q000821:virology; D014027:Tobacco Mosaic Virus / Q000502:physiology; D014170:Transformation, Genetic; D019076:Transgenes
C089425:N protein, Nicotiana glutinosa; D010940:Plant Proteins