The Use of Nicotiana Species in Tobacco Improvement

Abstract

There are more than 80 naturally occurring relatives of cultivated tobacco (Nicotiana tabacum L.) in the genus Nicotiana. In this review, we examine how and to what extent these natural germplasm resources have been utilized in hybridization and introgression experiments over the past century. To date, more than 400 interspecific Nicotiana hybrids have been reported. We focus on individual Nicotiana species involved in interspecific hybrids with cultivated tobacco produced by sexual and asexual methods, including the recently discovered grafting method. Problems related to the hybridization of N. tabacum with other species, namely, cross-incompatibility, maternal phenotypes in hybrid offspring, interspecific incongruity, lethality of juvenile hybrids, and sterility of viable hybrids, are reviewed. Among the 58 interspecific hybrids involving N. tabacum reported thus far, 25 were also reported as somatic hybrids and two were obtained only as somatic hybrids. Thirty-six sterile sexual F₁ hybrids were converted to fertile or partly fertile allopolyploids. Sixteen Nicotiana species have been deployed as a source of usable traits that were introgressed into N. tabacum, offering resistance to or tolerance of pathogens or pests. The mechanisms of introgression, such as alien addition and substitution, as well as the barriers and limitations of introgression, including erratic inheritance and adverse linkages, are discussed. Thirty-one Nicotiana species used as sources of cytoplasmic male sterility in N. tabacum have produced multiple alloplasmics; most showed negative effects of alien cytoplasm but a few have been deployed successfully in hybrid cultivars of N. tabacum.