Erwinia herbicola : A Bacterial Ice Nucleus Active in Increasing Frost Injury to Corn

LINDOW, S. E., D. C. ARNY, and C. D. UPPER. 1978. Erwinia herbicola: a bacterial ice nucleus active in increasing frost injury to corn. Phytopathology 68: 523-527. Cell suspensions of an isolate of Erwinia herbicola from a herbicola, frost damage was not significantly different from corn leaf were active in ice nucleation at -2.3 C and below, that to controls. The amount of damage increased greatly Ice nucleation activity was affected by the medium on which with increase in time of incubation between spraying and the cells were grown. Nucleation at -2.3 and -2.5 C was freezing, from 12 to about 36 hr. The amount of frost detected in suspensions of cells that had been grown on damage measured 48 hr after application of E. herbicola nutrient agar supplemented with 2.5% glycerol or glucose, suspensions increased as applied bacterial cell densities were respectively, but was detected only at temperatures below -4 increased. Erwinia herbicola began rapid multiplication C in cells grown on nutrient agar alone. Corn seedlings about 6 hr after the cells were sprayed onto leaves; sprayed with suspensions of this isolate of E. herbicola were populations of about 3 X 10 cells/g fresh weight of leaf at 6 hr severely damaged at -4 C, whereas control plants lacking leaf after inoculation had increased to about 5 X 106 cells/g after populations of E. herbicola or other bacteria active in ice 36 hr. Probit frost injury was directly proportional to the nucleation were not injured. If plants were frozen 6 hr or less logarithm of E. herbicola population (P <0.001). after they were sprayed with suspensions (10' cells/ml) of E. Additional key words: Zea mays, L., maize. Ice nuclei play a major role in frost damage to plants (3, identified from terrestrial sources were the bacteria, 11,14). Ice nuclei active at temperatures warmer than -5 Pseudomonas syringae van Hall (12) and P.fluorescens, C have been found on or near the surface of plants; e.g., a biotype G Migula (13). [Biologically derived ice nuclei, peeled lemon (surface nuclei removed) supercooled to including some from living marine phytoplankton, also about -9 C before freezing, whereas an intact lemon froze are available from oceanic sources (2, 19).] Thus, living at about -4 C (11). Ice nuclei have been presumed to be microorganisms, particularly a few species of bacteria, deposited on plant leaves from the atmosphere (11). apparently are abundant sources of very active ice nuclei. However, the nature, the source, and the abundance of ice We have reported recently that the presence of P. nuclei on plant leaves has not been reported until recently syringae on leaves of frost-sensitive plants prevents (1, 7, 8). Since ice nuclei are necessary for the initiation of supercooling and thus increases frost damage (1, 7, 9). ice formation even at temperatures much colder than -5 This report identifies another bacterial ice nucleus, C, and since any ice formation is damaging in frostErwinia herbicola (L6hnis) Dye, and demonstrates that sensitive plants such as corn (14), ice nuclei are important it, too, is active in promoting frost damage of frostdeterminants of frost damage to these plants. sensitive plants. Preliminary accounts of this work have In an attempt to identify natural sources of appeared (7, 10). atmospheric ice nuclei, Schnell and Vali (15) found a correlation between the content of ice nuclei and the MATERIALS AND METHODS content of organic matter in soils. Autoclaved soil lost all of its ice nucleation activity at temperatures warmer than The isolate of E. herbicola used in this study, obtained -10 C (16). Decaying leaf debris also contained many ice in July, 1975, from a corn leaf grown near Marxville, nuclei active at temperatures as warm as -5 C (15, 17). Wisconsin, was selected on the basis of its ice nucleation However, the most active ice nuclei that have been activity at -5 C. This yellow pigmented bacterium was identified as E. herbicola on the basis of its bacteriological 00032-949X/78/000 087$03.00/0 characteristics (5, 6). Unless otherwise specified, cultures Copyright © 1978 The American Phytopathological Society, 3340 were grown and maintained on nutrient agar fortified Pilot Knob Road, St. Paul, MN 55121. All rights reserved, with 2.5% glycerol.