THE GENETIC CONTROL OF PATHOGENICITY, SEROTYPES AND VARIABILITY IN PUCCINIA SORGHI

Abstract

Flangas, A. L., and J. G. Dickson. (U. Wisconsin, Madison.) The genetic control of pathogenicity, serotypes and variability in Puccinia sorghi. Amer. Jour. Bot. 48(4): 275–285. Illus. 1961.—Four urediospore clones of P. sorghi were inbred through the alternate host, Oxalis, and the recombinant lines were compared with the mother clones for changes in pathogenicity and serological reaction. The aecial, inbred recombinant lines were scored for pathogenicity on 6 inbred lines of maize, 4 of which contained single, dominant alleles isolated from a single gene locus each conditioning differential rust reaction and Pop 35 and Pop 36, each with 2 recessive genes. The inbred, recombinant lines from each of the 4 mother clones reflected similar dimensional changes from original pathogenicity, that is, an ultimate gain or loss in host range or specificity. Based on reaction type incited on the 4 allelic differential hosts, continued inbreeding through 3 generations did not segregate homozygous pathogenic complements into distinct pathogenic biotypes. A similar array of pathogenic types was produced after each generation of inbreeding. The suppressed pathogenicity types in the dicaryotic line were revealed only through recombination. Hybridization between dicaryotic lines of selected pathogenic types of sibling and nonsibling pedigree confirmed the indeterminate nature of the pathogenic locus. The genetic basis of the commonly occurring mesothetic‐X reaction (necrotic flecks and uredia of varying size surrounded by chlorotic and necrotic areas) is explained by the heterologous complementarity of fit of the interacting genic systems (genetic units). The heterologous mesothetic‐X reactions offer ambiguous definition to the specificity state of the interaction and cannot be explained on the discrete gene‐for‐gene basis of rust reaction. Antisera produced from the pathogenic types differentiated the homologous from the heterologous combinations and revealed cross‐reactions with P. graminis avenae. The comparative antigen constitution of the urediospore clones and the sibling recombinants thus far reveal a possible parallel existing between the modes of inheritance of pathogenic specificity and antigenic specificity.