Distribution, Population Dynamics, and Characteristics of Ice Nucleation-Active Bacteria in Deciduous Fruit Tree Orchards

Abstract

Deciduous fruit tree orchards located in the Pacific Northwest were surveyed over a 3-year period for the presence of ice nucleation-active (INA) bacteria. In the Yakima Valley, only about 30% of the fruit tree orchards contained INA bacteria (median population ca. 3 x 102 CFU/g [fresh weight]) in contrast to nearly 75% of the orchards in the Hood River Valley (median population ca. 5 x 103 CFU/g [fresh weight]). These INA populations ranged from less than 10 to over 106 CFU/g (fresh weight) of blossoms and, in Hood River Valley orchards, generally comprised over 10% of the total bacterial population. Populations of INA bacteria fluctuated during the year with highest levels developing on buds and flowers during the cool, wet spring, followed by a drop in populations during the warmer, drier, summer months and finally a gradual increase in the autumn. The INA bacteria persisted on dormant buds from which they again colonized young developing vegetative tissues. All INA bacteria were identified as Pseudomonas syringae. The frequency of ice nucleation at-5°C for these strains ranged from nearly every cell being INA to less than 1 in 107 cells. The median frequency of ice nucleation at-5°C was 104 cells per ice nucleus. The INA P. syringae strains from individual orchards were diverse with respect to bacteriocin typing and in ice nucleation frequency. The consistent absence of detectable INA bacteria or presence of low populations in most of the orchards surveyed during periods when critical temperatures (i.e.,-2 to-5°C) were common indicated a limited role for INA bacteria in frost susceptibility of most Pacific Northwest orchards.

The Role of Ice Nucleation-active Bacteria on Frost Damage of Tea Plants.

“…Therefore, it could be concluded that INA bacteria have only minor importance, if any, on the initiation of frost damage of tea plant. The similar relationships between INA bacteria and frost damage have already reported in the field oriented research e.g., frost damage of deciduous fruit trees such as peach and sweet cherry3, 5,11,12) Literature cited…”

Effects of sulfate coatings on the ice nucleation properties of a biological ice nucleus and several types of minerals

“…Note that although SNOMAX is made from cells of P. syringae, it does not display the same freezing spectrum (fraction frozen vs. temperature) as some naturally occurring strains of P. syringae. Also note that the freezing spectrum of naturally occurring P. syringae can vary significantly from strain to strain [Gross et al, 1983;Hirano et al, 1985;Möhler et al, 2008b;Ward and DeMott, 1989].…”

Raindrop Momentum Triggers Growth of Leaf-Associated Populations of Pseudomonas syringae on Field-Grown Snap Bean Plants

“…Associations of large population sizes of P. syringae with rain and temperature have been reported for a number of plant species grown in different geographic areas (4,5,7,8,10,21,28,32,38). For example, large population sizes of P. syringae were found on leaves of stonefruit trees grown in Victoria, Australia, when rainfall was moderately high and temperatures ranged from 19 to 25ЊC (38), on buds and flowers of pome and stonefruit trees in the Pacific Northwest when rainfalls were frequent and temperatures were relatively cool (10), and on leaves of tomato plants grown in Georgia when moisture levels were high and temperatures were low (32). It has been generally assumed that the large population sizes of P. syringae associated with rains are due to the availability of moisture for bacterial growth.…”

“…Fluctuations in relative abundance are a common attribute of populations in nature, including bacteria that inhabit the phyllosphere (i.e., leaves) (6,10,12,33). To begin to identify and understand the factors that bring about or contribute to changes in phyllosphere bacterial population sizes, we have focused our studies on the bacterium Pseudomonas syringae.…”