Leifsonia
Encyclopedia
Leifsonia xyli subsp. xyli is a small, fastidious, Gram-positive, coryneform bacterium that causes ratoon stunting disease
, a major worldwide disease of sugarcane
.
., a taxonomic order that contains other genera of plant pathogens of great agricultural impact, including Clavibacter, Curtobacterium
, and Streptomyces
.
in its centre of diversity, Papua New Guinea
, which suggests either it has recently evolved to infect its host, or has been acquired from a related species. 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 .
s suggestive of an ongoing process of genome decay. L. xyli subsp. xyli has been proposed as once a free-living bacterium, but is now restricted to the xylem as a consequence or cause of the accumulation of pseudogenes. This point stems from the observation although L. xyli subsp. xyli has only been detected inhabiting the xylem of sugarcane, it carries several genes typical of free-living organisms.
Ratooning
Ratooning is a method which leaves the lower parts of the plant along with the root uncut at the time of harvesting to give the ratoon or the stubble crop. The main benefit of ratooning is that the crop matures earlier in the season...
, a major worldwide disease of sugarcane
Sugarcane
Sugarcane refers to any of six to 37 species of tall perennial grasses of the genus Saccharum . Native to the warm temperate to tropical regions of South Asia, they have stout, jointed, fibrous stalks that are rich in sugar, and measure two to six metres tall...
.
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. Leifsonia xyli subsp. xyli is a fastidious member of the GC-rich ActinomycetalesActinomycetales
Actinomycetales is an order of Actinobacteria. They are very diverse and contain a variety of subdivisions as well as yet unclassified isolates. This is mainly because some genera are very difficult to classify because of a highly niche-dependent phenotype...
., a taxonomic order that contains other genera of plant pathogens of great agricultural impact, including Clavibacter, Curtobacterium
Curtobacterium
Curtobacterium is a genus of bacteria of the order Actinomycetales. They are Gram-positive soil organisms....
, and Streptomyces
Streptomyces
Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described. As with the other Actinobacteria, streptomycetes are gram-positive, and have genomes with high guanine and cytosine content...
.
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.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 officinarumSugarcane
Sugarcane refers to any of six to 37 species of tall perennial grasses of the genus Saccharum . Native to the warm temperate to tropical regions of South Asia, they have stout, jointed, fibrous stalks that are rich in sugar, and measure two to six metres tall...
in its centre of diversity, Papua New Guinea
Papua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
, which suggests either it has recently evolved to infect its host, or has been acquired from a related species. 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 .
Symptoms
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 pseudogenePseudogene
Pseudogenes are dysfunctional relatives of known genes that have lost their protein-coding ability or are otherwise no longer expressed in the cell...
s suggestive of an ongoing process of genome decay. L. xyli subsp. xyli has been proposed as once a free-living bacterium, but is now restricted to the xylem as a consequence or cause of the accumulation of pseudogenes. This point stems from the observation although L. xyli subsp. xyli has only been detected inhabiting the xylem of sugarcane, it carries several genes typical of free-living organisms.