Characterization of Wheat Genotypes as Sources of Ice Nucleation Active Bacteria for Bioprecipitation Aerosols

Abstract

As water resources become more and more scarce, production of crops under dry land conditions brings agriculture into potential conflict with other uses of water. There is an emerging awareness that the orientation of the goals of plant breeding can be shifted to create crops that can offset the negative impacts of agriculture on the environment in order to make agriculture more sustainable. Here we have explored the possibility to select lines of wheat, the crop that occupies more land than any individual crop, that contribute to the bioprecipitation cycle. In this cycle the ice nucleation (IN) active component of the microflora on leaves contributes to the ice nuclei in the atmosphere that activate processes in clouds necessary for rainfall. In line with this long term goal, we have deter-mined the capacity of breeding lines of wheat, adapted to dry land conditions, to harbor IN active bacteria.  In particular, we focused on Pseudomonas syringae, the most ubiquitous of the IN active bacteria on plants.  Because strains of this bacterium can be a plant pathogen, we evaluated the abundance of non-pathogenic IN active strains of P. syringae on a range of wheat genotypes from the research program of the International Center for Agricultural Research in the Dry Areas. Of the 25 genotypes of bread wheat examined, leaves of 12 genotypes naturally harbored P. syringae in the field.  Eight of these genotypes harbored populations of IN active P. syringae with an impaired Type 3 Secretion System (involved in pathogenicity) as high as 4 x 105 105 CFU g-1 of leaf tissue. Three of these 8 wheat genotypes harbored IN active P. syringae that were not virulent on either bread or durum wheat and for 1 of these wheat genotypes the strains of IN active P. syringae were virulent on only 1 of the 13 plant species on which pathogenicity was tested. For the wheat geno-types that had P. syringae on leaves in the field, bacteria were naturally transmitted to seed but dur-ing seed storage the bacterium could be detected on only half of the genotypes after 3 months of storage. To explore the possibility of enhancing the IN active microflora on leaves, we assessed the capacity of bacteria inoculated on seed to be transmitted to seed.  The effectiveness of the trans-mission depended on an interaction of wheat genotype and bacterial strain. Overall, this work points to the possibility of selecting plants with the goal of changing their microflora for purposes other than resistance to plant disease and in this case for the purpose of contributing to processes that could favor rainfall.