Studies in the inheritance of Disease-Resistance

Abstract

On crossing immune and susceptible varieties the resulting offspring is susceptible. On self-fertilization these susceptible individuals produce immune and susceptible descendants in the proportion of one of the former to three of the latter. The degree of susceptibility is variable. Where the degree of susceptibility differs in the two parents the hybrid resembles the more susceptible parent in that respect. Among the descendants of such hybrids the two degrees of susceptibility appear in the usual Mendelian ratio of one slightly to three very susceptible individuals. The relatively immune forms breed true to this characteristic in the succeeding generations. Immunity is independent of any discernible morphological character, and it is practicable to breed varieties morphologically similar to one another, but immune or susceptible to the attacks of certain parasitic fungi.