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Ecology and Epidemiology

A Relationship between Ice-Nucleation-Active Bacteria, Freeze Damage, and Genotype in Oats. D. Marshall, The Texas Agricultural Experiment Station, Texas A&M University Research and Extension Center, 17360 Coit Road, Dallas 75252; Phytopathology 78:952-957. Accepted for publication 12 February 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-952.

Field and laboratory studies were conducted over a 2-yr period to determine if ice-nucleation-active (INA) bacteria played a role in the freeze damage of three oat cultivars and if cultivar:bacteria interactions were present. The winter-tender cultivar Florida 501 sustained greater freeze damage and supported higher populations of INA bacteria than did the moderately tender cultivar Coronado or the moderately hardy cultivar H-833. Populations of INA bacteria were 10²–10⁴ times greater on Florida 501 than on H-833. Field applications of Agristrep and Kocide 101 significantly reduced freeze damage and increased forage and grain yields of the three cultivars. Plots inoculated with an INA isolate of Pseudomonas syringae produced less forage and grain and had greater freeze damage than uninoculated plots. In a greenhouse and growth chamber study, the ability of individual plants to withstand freeze damage was tested at –4 C, for exposure times of 2–48 hr. Leaves of H-833 sustained freeze damage at a slower rate and supported fewer INA bacteria than Coronado or Florida 501. Although Coronado had the same detectable levels of INA bacteria as Florida 501, its leaves froze at a slightly slower rate than did leaves of Florida 501. When drenched in a mixture of Agristrep and Kocide 101, leaves of Florida 501 and Coronado had some freeze damage after 36 hr of exposure, while H-833 had no freeze damage up to 48 hr. The results suggest that INA bacteria as well as nonmicrobial factors were responsible for freeze damage in oats. Additionally, oat cultivars were found to differ in their resistance to INA bacteria, and in H-833, this resistance was expressed as a slow-freezing.