Leifsonia

Taxobox
color = lightgrey
name = "Leifsonia xyli"
regnum = Bacteria
phylum = Actinobacteria
ordo = Actinomycetales
suborder = Micrococcineae
familia = Microbacteriaceae
subsp = "xyli"
genus = "Leifsonia"
binomial = "Leifsonia xyli"
subdivision_ranks = Subpecies
subdivision = "Leifsonia xyli" subsp. "xyli"

"Leifsonia xyli" subsp. "xyli" is a small, fastidious, Gram-positive, coryneform bacterium that causes ratoon stunting disease, a major worldwide disease of sugarcane.

Classification

Formerly classified as "Clavibacter xyli" subsp. "xyli", it was removed from the genus "Clavibacter" to create the genus "Leifsonia", together with "L. poae", found in "Poa annua" root galls, and "L. aquatica", a free-living bacterium.cite book |author= Monteiro-Vitorello et al|year=2009|chapter=Genome Sequence-based Insights into the Biology of the Sugarcane Pathogen Leifsonia xyli subsp. xyli |title=Plant Pathogenic Bacteria: Genomics and Molecular Biology|publisher=Caister Academic Press|id= ISBN 978-1-904455-37-0] "Leifsonia xyli" subsp. "xyli" is a fastidious member of the GC-rich Actinomycetales., a taxonomic order that contains other genera of plant pathogens of great agricultural impact including "Clavibacter", "Curtobacterium", and "Streptomyces".cite book | author = Jackson RW (editor). | title = Plant Pathogenic Bacteria: Genomics and Molecular Biology | publisher = Caister Academic Press | year = 2009 | id = ISBN 978-1-904455-37-0 ]

Disease

Ratoon stunting disease is the most economically important disease of sugarcane and is found in most sugarcane growing areas of the world. It can cause yield losses of up to 30% in susceptible varieties. The disease is difficult to identify and is transmitted mechanically or through infected seeds.cite book |author= Monteiro-Vitorello et al|year=2009|chapter=Genome Sequence-based Insights into the Biology of the Sugarcane Pathogen Leifsonia xyli subsp. xyli |title=Plant Pathogenic Bacteria: Genomics and Molecular Biology|publisher=Caister Academic Press|id= ISBN 978-1-904455-37-0]

Transmission

Since the bacterium is present in the liquids of infected plants, it can be mechanically disseminated after contamination of the cane knives used in harvesting. Thus, the incidence of infected plants increases during successive ratoon crops. For this reason and for quite some time, cumulative losses due to the disease have probably been greater than the losses caused by any other sugarcane disease.

Evolution

The bacterium has never been found affecting wild clones of "Saccharum officinarum" in its centre of diversit, Papua New Guinea, which suggests it has recently evolved to infect its host. It is believed to have evolved from a single pathogenic clone, since no genetic variation was found among different isolates of distinct countries and cultivars.

ymptoms

Symptoms are highly dependent on the genetic background of the varieties and on environmental conditions. Because of this, the spread of the disease through planting material has beset most sugarcane growing areas in the world. Infected plants show reduced cane diameter and shortening of the internodes, i.e., stunting. Discolouration of vascular bundles of mature stalks may be seen in the form of discrete rosy dots or streaks just below the internodes where the bundles branch into the leaf sheath, but this is of little diagnostic value as infection by other pathogens may cause the same symptom.

Genetics

"Leifsonia xyli" subsp. "xyli" has a relatively large number of pseudogenes suggestive of an ongoing process of genome decay. It has been proposed that "Leifsonia xyli" subsp. "xyli" was once a free-living bacterium that is now restricted to the xylem as a consequence or cause of the accumulation of pseudogenes. This point stems from the observation that although "Leifsonia xyli" subsp. "xyli" has only been detected inhabiting the xylem of sugar cane, it carries several genes typical of free-living organisms.cite book |author= Monteiro-Vitorello et al|year=2009|chapter=Genome Sequence-based Insights into the Biology of the Sugarcane Pathogen Leifsonia xyli subsp. xyli |title=Plant Pathogenic Bacteria: Genomics and Molecular Biology|publisher=Caister Academic Press|id= ISBN 978-1-904455-37-0]

References