Fastidious Prokaryotes and Plant Health

Abstract

The prokaryotes are almost everywhere or we can phrase like this “prokaryotes are wherever there is life”. They were the earliest organisms on earth. Today, they still dominant the biosphere for the following two facts: 1) their collective biomass outweighs all eukaryotes combined at least tenfold, and 2) more prokaryotes inhabit a handful of fertile soil or the mouth or skin of a human than the total number of people who have ever lived. They thrive in habitats that are too cold, too hot, too salty, too acidic, or too alkaline for any eukaryote because they display diverse adaptations that allow them to inhabit many environments and they have great genetic diversity. Phytopathogenic fastidious prokaryotes are plant pathogens that either resist to grow in any available bacterial culture media or require specific or enriched media to grow. They include Xylella fastidiosa, Leifsonia xyli subsp. xyli, L. xyli subsp. cynodontis and Clavibacter michiganensis subsp. sepedonicus and C. michiganensis subsp. michiganensis that reside in xylem and spiroplasmas, phytoplasmas and Candidatus Liberibacter spp. that reside in phloem. The impacts that fastidious prokaryotes have on plant health have been enormous. Two major maladies caused by X. fastidiosa resulted in serious economic loss on wine and citrus juice industry. Three plant diseases, namely citrus stubborn, corn stunt and periwinkle diseases are caused by spiroplasmas. Over 500 plant diseases were reportedly the results of phytoplasmal infestation (22). Ca. Liberibacter spp., are the causal agents of decades-long citrus disease called Huanglongbing or citrus greening and the recent-emerged zebra chip disease of potato and others. Pierce’s disease is the limiting factor for the establishment of wine industry for the entire southeastern United States from Texas to the Carolinas along the gulf coast of Mexico. Recent introduction of the glassy-winged sharpshooter leafhoppers in California has threatened the winery industry of California. The successful isolation of X. fastidiosa from the tissues with citrus variegated chlorosis (CVC) symptoms followed by the identification of the major insect vectors provided crucial information for citrus growers and citrus juice industry to deal with the CVC crisis in Brazil. The successful isolation of X. fastidiosa from blueberry tissues with leaf scorch symptoms followed by the identification of the susceptibility/resistance of various blueberry cultivars provided significant information for the blueberry industry which has recently become the number one fruit commodity in Georgia.