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Inheritance of Pathogenicity in Setosphaeria turcica. Ali H. Hamid, Former Graduate Student, Department of Plant Pathology, University of Hawaii, Honolulu, Hawaii 96822; M. Aragaki, Plant Pathologist, Department of Plant Pathology, University of Hawaii, Honolulu, Hawaii 96822. Phytopathology 65:280-283. Accepted for publication 30 September 1974. DOI: 10.1094/Phyto-65-280.

Of 47 field isolates of Setosphaeria turcica, 18 were virulent only to the host species from which each was isolated; whereas the remaining 29 were virulent to at least one other host. Virulence to corn and sorghum were inherited independently, as indicated by a 1:1:1:1 segregation for virulence to corn alone, sorghum alone, both corn and sorghum, and avirulence to both hosts from a cross between a corn specific isolate and an isolate virulent to both sorghum and Johnsongrass. Common occurrence of field isolates with virulence to both corn and sorghum, combined with independent inheritance of virulence to these two hosts, suggest that these could be treated as a third specialized form, S. turcica f. sp. complexa. Among ascospore isolates virulent to sorghum, approximately 75% were also virulent to Johnsongrass, suggesting that factors conditioning virulence to these two hosts are linked. On the basis of this apparent linkage and the congeneric relationship of these hosts, isolates virulent to Johnsongrass should be included in S. turcica f. sp. sorghi. Compatibility was inherited independently of virulence to corn in two crosses. In a third cross, compatibility was independent of virulence to sorghum and Johnsongrass also. Among ascospore isolates avirulent to corn, three reactions (viz. chlorosis, fleck, and nonpathogenicity) were observed. Ascospore isolates avirulent to sorghum either incited flecks, or were symptomless on sorghum.