Bacterial Ice Nucleation Research Articles

Reduction of Bacterially Induced Frost Damage to Tender Plants

Abstract Strategies for reducing bacterially induced frost damage to tender plants were examined. Introduction of the competitive bacterium, Erwinia herbicola M232A (not active in ice nucleation) did not lower the temperature at which freeze injury of tomato shoots occurred. Streptomycin was effective in reducing freeze damage of tomato shoots only when mixed with the Pseudomonas syringae suspension prior to plant inoculation. Spectinomycin, another aminoglycoside, was effective in reducing frost damage to tomato plants due to P. syringae. Bacteria present intercellularly (within the plant) may play a significant role in bacterial ice nucleation.

Reduction of Frost Injury to Almond by Control of Ice Nucleation Active Bacteria

Abstract Epiphytic populations of ice nucleation active (INA) strains of Pseudomonas syringae van Hall of up to 106cells/g fresh weight were found on healthy tissues of commercially managed almond [Prunus dulcis (Mill.) D.A. Webb] orchards in California. Leaf bacteria accounted for over 99% of the ice nuclei active at temperatures higher than − 5°C on almond. Large, seasonal variations in populations of INA bacteria and ice nuclei on almond were observed, with maximum populations found shortly after full bloom. These populations were reduced from 10- to 100-fold by 3 weekly applications of bactericides starting at budbreak, or a single application at 10% bloom of a nonice nucleation active antagonistic bacterium isolated from an almond leaf surface. Applications of cupric hydroxide to dormant tissues and/or to growing tissue after budbreak were most effective at reducing populations of INA bacteria and ice nuclei on almond. Application of bacterial ice nucleation inhibitors did not influence populations of INA bacteria on almond shoots shortly after application, but reduced the numbers of ice nuclei active at −5° or warmer. Frost injury to detached almond spurs cooled to −3° was reduced by all treatments that reduced the numbers of bacterial ice nuclei on almond tissue.

The Role of Bacterial ICE Nucleation in Frost Injury to Plants

The science of plant pathology is largely a study of the mechanisms, quantifica­ tion, and alleviation of plant stresses due to biological agents. Of obvious importance are the stresses to plants directly caused by infection by various plant pathogenic fungi, bacteria, viruses, nematodes, insects, etc. In such cases, plant stress is due either to direct damage to plant tissue or to an alteration in normal plant metabolism (43). Some biological agents, such as the fungi that form mycorrhizae with plant roots, may even reduce plant stress in certain situations and increase stress in others (4). Plants may also be stressed directly and indirectly by various physical factors such as high or low temperatures (57) or air pollutants (36). A wealth of information exists on the direct effects of low temperatures (57) or air pollu­ tants (36) on plant health. Physical stresses such as temperature (57) or air pollutants (36) may also influence the subsequent damage of plants incited by certain plant pathogens. The converse is also true in some situations. Root­ infecting plant pathogens, for example, can make plants more susceptible to damage due to high temperatures or drought. It is clear that the interaction of the biological and physical environments of plants determines the extent of plant stress. Many more subtle interactions between microorganisms and plants have also been reported. Bacteria living on the surfaces of healthy leaves and roots have been reported to increase plant growth, possibly by production of one or more plant growth regulators (86). Conversely, some bacteria isolated from root surfaces have been shown to be detrimental to root and p,lant growth (117). Frost injury is a serious abiotic disease of plants. Losses in plant production

Bacterial Ice Nucleation: A Factor in Frost Injury to Plants

Heterogeneous ice nuclei are necessary, and the common epiphytic ice nucleation active (INA) bacteria Pseudomonas syringae van Hall and Erwinia herbicola (Löhnis) Dye are sufficient to incite frost injury to sensitive plants at -5 degrees C. The ice nucleation activity of the bacteria occurs at the same temperatures at which frost injury to sensitive plants occurs in nature. Bacterial ice nucleation on leaves can be detected at about -2 degrees C, whereas the leaves themselves, i.e. without INA bacteria, contain nuclei active only at much lower temperatures. The temperature at which injury to plants occurs is predictable on the basis of the ice nucleation activity of leaf discs, which in turn depends on the number and ice nucleation activity of their resident bacteria. Bacterial isolates which are able to incite injury to corn at -5 degrees C are always active as ice nuclei at -5 degrees C. INA bacteria incited frost injury to all of the species of sensitive plants tested.