Inheritance and recombination of strain-specific characters in tobacco streak virus

Abstract

The genetics of symptom determinants and serological type of tobacco streak virus (TSV) were investigated by picking single-lesion hybrid clones of virus originating from heterologous combinations of nucleoprotein components of strains with contrasting characters. A dwarfing of chronically diseased Xanthi-nc tobacco leaves required two factors from different components of the HF strain. In hybrid clones between HF and other strains, each factor was usually, but not always, perpetuated in the component that had provided it to the cross, and was masked. Its presence was demonstrated by backcrossing the hybrid to the HF parent or by crossing with other hybrid clones carrying a single dwarfing determinant in the complementary component. Factors conditioning toothed (t) or entire (e) margins on chronically diseased leaves were carried in each of the particle types. These factors were mutually exclusive when both were present in heterologous combinations of particles, the functional type apparently being determined by chance. The presence of two d (dwarfing) determinants masked t or e determinants, but did not prevent their replication. A determinant conditioning failure of Xanthi tobacco to recover from necrotic symptoms was carried only in the top component, and disappeared from functional particles on aging. Determinants for two serological types were also mutually exclusive and were carried by all three particle types. There appeared to be a linkage between the dwarfing determinants and the serological determinants. Recombinations of other characteristics (lesion type on Vigna cylindrica, chronic symptoms on Xanthi tobacco, and serological type) appeared about as often as would be expected on the basis of random assortment. Redundance in genetic information among particle types of TSV is common; recombination greatly increases variation.