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Temperature and Light Effects on Cultural Differences Between Races T and O of Helminthosporium maydis. Kate A. Fukuki, Graduate Assistant, Department of Plant Pathology, University of Hawaii, Honolulu 96822; M. Aragaki, Associate Plant Pathologist, Department of Plant Pathology, University of Hawaii, Honolulu 96822. Phytopathology 62:676-678. DOI: 10.1094/Phyto-62-676.

Colonies of race T were white except for cinnamon rufous to russet centers, whereas cultures of race O were dark olive gray when grown at 28 C under continuous fluorescent illumination. This cultural distinction also involves differences in sporulation. Optimum sporulation for isolates of race O was between 20-28 C in continuous light and 28 C in darkness. Optimum sporulation of race T isolates was 20 C under continuous illumination, and 24 C in continuous darkness. At high temperatures, race T was more sensitive than race O to inhibition of sporulation by light.