Yield, chemistry, quality, and soilborne pathogen resistance of nearly isogenic low-alkaloid lines of flue-cured tobacco

Mandated lowering of nicotine levels in combustible cigarettes is under consideration by some regulatory agencies. Technical feasibility of genetics-based strategies to achieve ultra-low nicotine levels (0.4–0.7 mg g⁻¹) in cured tobacco leaves in the absence of undesired correlated changes requires field evaluation. Use of naturally occurring or conventionally induced genetic variation to achieve this potential goal would likely be preferred. In this research, we generated 11 nearly isogenic lines (NILs) of flue-cured tobacco cultivar K326 or K326-like genotypes possessing different types of allelic variability affecting lower nicotine accumulation. Ten low-nicotine genotypes were evaluated in comparison with K326 in four field environments under conventional agronomic management. Only three NILs accumulated nicotine in weighted composite cured leaf samples at levels less than 0.7 mg g⁻¹. These materials displayed significant negatively altered cured leaf quality, however. Significantly reduced soilborne pathogen resistance was also observed in two of the lowest nicotine NILs. We also evaluated in two field environments nic1/nic1 nic2/nic2 NILs of K326, which possessed either the transcriptionally suppressed nic1 allele derived from LAFC53 or a nic1 deletion allele derived from TI 313. The latter NIL was found to accumulate significantly lower alkaloid levels but produced unacceptable cured leaf yields that were 47.6% lower than that for K326. Results suggest that it is not straightforward to develop ultra-low nicotine cultivars without unfavorably altering other characteristics, at least using currently characterized naturally existing or induced genetic variability.