Bull. Spec. CORESTA Congress, Harare 1994, p. 139, PPOST 12

Genetic basis of tobacco disease resistance - problems and achievements

D. Kostov Inst. of Genetics, Bulgarian Academy of Sciences, Sofia, Bulgaria
The problem of tobacco disease resistance is complicated and it depends on the interactions between both genetic systems - host plant and pathogen - in the environmental conditions. The present investigation includes the following aspects : identification of genes for resistance and study on interactions between them; determination of pathogen diversity of disease agents in Bulgaria; elucidation of genetic mechanisms of regulation of host-pathogen interactions; preservation and enrichment of resistance gene bank; selection of tobacco disease-resistant lines and cultivars. The results of the investigations include the genetics of tobacco resistance to Peronospora tabacina Adam, Erysiphe cichoracearum D.C. Ph., Phytophthora parasitica var. nicotiana, TMV, ToMV and PVY. The sources of genes for resistance to widespread populations of these pathogens are identified, which are mainly species of genus Nicotiana . By use of interspecific hybridization and in vitro methods, genes for resistance to blue mold, powdery mildew and black shank are successfully transferred from N. debneyi and N. goodspeedii to tobacco genome. Efficiency of known genes for resistance to the above mentioned pathogens is established and the gene interactions are determined. Gene bank from resistant forms is created and 7 resistant cultivars are obtained. The virulence of most of the pathogens is recessive inherited. According to the proposed hypothesis, the genetic mechanisms of host-pathogen interactions can be regulated by creation of diverse gene bank from disease resistant forms, that leads to strengthening of parasitic properties of pathogens, accumulation of recessive genes in them, and weakening of their populations.