Cultural Variance of Alternaria carthami Isolates and Their Virulence on Safflower. K. Mortensen, Former Postdoctoral Research Associate, Montana State University, Bozeman 59717. J. W. Bergman, Associate Professor of Agronomy, Montana Agricultural Experiment Station, Eastern Agricultural Research Center, Sidney 59270. Plant Dis. 67:1191-1194. Accepted for publication 25 May 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-1191.

Thirty-five isolates of Alternaria carthami from leaves of safflower (Carthamus tinctorius) in field plots and from naturally infected safflower seeds were variable in culture on potato-carrot agar but all were virulent on safflower cultivars and breeding lines tested. Symptoms appeared as irregular necrotic lesions on leaves and stems, similar to stem and leaf spots occurring under natural conditions. Lesions often coalesced, leaving large areas of the plants necrotic. Higher levels of resistance to A. carthami were detected in some breeding lines compared with safflower cultivars US-10, Gila, and S208. A. carthami, A. solani, A. alternata, and Stemphylium vesicarium penetrated healthy leaves of safflower. Infections by A. solani, A. alternata, and S. vesicarium did not cause leaf spots on healthy safflower leaves but the fungi remained dormant until leaf senescence.