Influence of Interrupted Dew Periods, Relative Humidity, and Light on Disease
Severity and Latent Infections Caused by Cercospora kikuchii on Soybean. W.
Schuh. Assistant professor, Department of Plant Pathology, The Pennsylvania
State University, University Park 16802. Phytopathology 83:109-113. Accepted for publication
16 September 1992. Copyright 1993 The American Phytopathological Society. doi:10.1094/Phyto-83-109.
Germination of Cercospora kikuchii conidia, at 25 C, with relative
humidities of 100% wet, 100% dry, and 99%, was influenced by light-period
regime. Germination was significantly lower at 24 h of light (35.6%) compared to
24 h of dark, to, sequentially, 12 h of light/12 h of dark, and to,
sequentially, 12 h of dark/12 h of light. Identical light treatments (25 C and
24 h of leaf wetness) had a similar, significant effect (P = 0.05) on
disease severity, based on pairwise comparisons. When ranked, 12 h of dark/12 h
of light was most conducive to infection, followed in descending order by 24 h
of dark, 12 h of light/12 h of dark, and 24 h of light. Interruption of 24-h
leaf-wetness periods for 4, 8, 12, and 16 h after an initial wetness period of
12 h had a significant influence on disease severity and on the number of latent
infections. The effect depended on the relative humidity during the
interruption. High-relative humidity (>95%) resulted in higher disease severity
and number of latent lesions with increases in interruption periods, whereas
low-relative humidity (~55%) resulted in lower values. The relationship between
duration of leaf-wetness interruption and disease severity versus number of
latent infections was statistically significant (P = 0.01) under both
relative humidities. Additionally, there was evidence that the posttreatment
relative-humidity conditions influenced the number of latent infections.