Importance of Alternaria carthami and A. alternata in Causing Leaf Spot Diseases of 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; and E. E. Burns, Former Extension Plant Pathologist, Montana State University, Bozeman 59717. Plant Dis. 67:1187-1190. Accepted for publication 25 May 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-1187.

Isolations from leaf spots on field-grown safflower (Carthamus tinctorius) in Montana in 1976 in early stages of development yielded Alternaria carthami almost exclusively, whereas toward maturity, A. alternata was predominant. Under greenhouse conditions, A. carthami was pathogenic on safflower at all growth stages. A. alternata also infected healthy safflower plants but infections remained dormant until leaf senescence. Both fungi were isolated from safflower seeds. Four seed-treatment fungicides provided only partial control of these fungi in field and greenhouse tests. Seed produced in Arizona were nearly free of these fungi, whereas seed produced under wetter conditions in Montana were heavily infested with A. carthami and A. alternata and had inferior germination and seedling vigor.

Keyword(s): conidia trapping.