Effect of Temperature and Growth Stage of Wheat on Development of Leaf and Glume Blotch Caused by Septoria tritici and S. nodorum. S. J. Wainshilbaum, Former Graduate Student, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. P. E. Lipps, Associate Professor, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. Plant Dis. 75:993-998. Accepted for publication 9 April 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0993.

Severity of leaf blotch caused by Septoria tritici and leaf and glume blotch caused by S. nodorum was assessed on two soft red winter wheat cultivars (AGRA GR855 and Caldwell) at three temperatures (19, 24, and 29 C) and four growth stages (GS 6 or first node visible, GS 10 or boot, GS 10.5 or preflowering, and GS 11 or postflowering). The percentage of leaf and glume area with symptoms, density of pycnidia in lesions, and number of conidia per pycnidium were determined. Analysis of variance (ANOVA) for area under the disease progress curve (AUDPC) indicated that S. tritici caused similar levels of disease at 19 and 24 C but very low levels of disease at 29 C. Growth stage had no effect on disease severity caused by S. tritici (P = 0.05). S. nodorum caused relatively high levels of disease at each temperature tested, but no significant differences for AUDPC were detected for temperature (P = 0.05). AUDPC values for Septoria nodorum leaf blotch were significantly higher (P = 0.05) at each succeeding growth stage tested for AGRA GR855, and AUDPC values for Caldwell were significantly greater at GS 11 than GS 6 or 10. The density of pycnidia and numbers of conidia per pycnidium on leaf lesions were higher for S. tritici than for S. nodorum. S. tritici caused only low levels of glume blotch at 19 and 24 C and none at 29 C, whereas S. nodorum caused relatively high levels of glume blotch at each temperature tested. Results indicated the level of leaf blotch incited by S. tritici was more influenced by temperature than growth stage at time of inoculation, and leaf blotch incited by S. nodorum was affected more by plant growth stage at time of inoculation than temperature. This suggests an explanation for the seasonal occurrence of these two pathogens. The cooler temperatures of early spring favor development of leaf blotch caused by S. tritici. The greater prevelance of S. nodorum later in the season may be a consequence of increasing susceptibility of the wheat plant to this pathogen as it matures.