The role of top particles in recombination of some characters of tobacco streak virus

Abstract

Inoculations were made with mixtures of middle and bottom, and with top, middle, and bottom particles of a tobacco streak virus strain causing large chlorotic lesions and another strain causing small red lesions on Vigna cylindrica. Some of the resulting lesions were large red, and a smaller number were small chlorotic, types representing recombinations of lesion size and lesion color. Recombinants occurred most frequently when mixtures contained top particles, which more often contributed the determinant for lesion size to progeny than the determinant for lesion color. The stability of the characteristics of recombinant hybrids was demonstrated by subculturing and by backcrossing. The determinants for dwarfing of tobacco were usually carried, in hybrid virus clones, in the particle type in which they were introduced into a cross. The determinants for serological type reassorted apparently randomly among hybrid clones. Top particles contributed genetic determinants which were carried in middle or bottom particles of hybrid offspring. Conversely, from crosses of middle and bottom particles, top particles of hybrids carried genetic determinants derived from middle or bottom particles. Top particles contributed less than middle or bottom particles to the infectivity of mixtures of three particle types. It seemed doubtful that top particles contained much, if any, genetic information not also carried in middle and bottom particles.