Genetic studies in crosses between Sphacelotheca reiliana (Kühn) Clint. and S. sorghi (Lk.) Clint

Abstract

Interspecific crosses among haploid progenies from one teliospore of Sphacelotheca reiliana and one teliospore of S. sorghi were made. A high degree of compatibility was found among haploid lines of the two species. With few exceptions, the morphology of the F₁ sorus was like that of the covered smut parent. On the average, the spores of the F₁ generation were intermediate in size and echinulation. The F₁ spores germinated by producing promycelia and sporidia that displayed heterosis. These promycelia were more than twice the length of either parental type. Differences in size and morphology of the spores and length of promycelium were found within F₁ hybrids of the same cross. This suggested that some genetic recombination preceding teliospore formation must have taken place in these species. Segregation for sorus and spore characters was obtained in the F₂ generation. Although all the characters studied appeared to be independently inherited in some isolates, in other isolates the characters of covered smut seemed to be very closely linked. Segregation for pathogenicity was also obtained in the F₂ generation, and new pathogenic types were obtained as a result of hybridization. Characters such as sorus morphology, color of peridium, and some characters pertaining to the spores, are influenced to an extent by the variety in which they are produced. Characters such as percentage of germination, mode of infection, and in certain cases, symptomatology are suggested as reliable genetic markers for studies on variability in these species.