Scientists at four major genomics and plant pathology laboratories in China have collaborated to find the causative agent of "black rot" disease, the most serious disease of vegetable crops worldwide.
Indeed for commercial growers, black rot is a significant issue. The fact that thepathogen can be seed-borne has led to seed certification programmes in developed countries, adding extensive cost and effort for suppliers and producers.
And if an outbreak does occur, then whole crops can be devastated.
This is because there is no effective treatment for Xcc infection. But now a team of scientists at four Chinese institutions - the Institute of Microbiology at the Chinese Academy of Sciences, the Chinese National Human Genome Center at Shanghai, Guangxi University, and the Chinese National Human Genome Center at Beijing - have focused their efforts on characterising the genes responsible for Xcc pathogenicity with a view to finding a cure.
Black rot is caused by the pathogenic bacterium Xanthomonas campestris pathovar campestris (or Xcc). Under favourable conditions - high humidity and temperature - Xcc infects vegetable crops by spreading through the plants' vascular tissues, turning the veins in their leaves yellow and black, and causing V-shaped lesions along the margins of the leaves.
In their study, the team from China describe the identification of 75 different genes responsible for Xcc virulence. These genes appear to belong to 13 different functional categories or related metabolic pathways.
The researchers believe that the molecular characterisation of these pathogenicity-related genes will lead to the development of a treatment for "black rot" disease.
Employing whole-genome comparative genomic approaches, the scientists sequenced the complete genome of an Xcc strain that was isolated from an infected cauliflower plant in England during the 1950s. They then compared this sequence to a previously published sequence from a cabbage-derived Xcc strain.
Interestingly, they were able to identify three genes that were implicated in pathogenicity but that were not present in the previously described Xcc genomic sequence. To test the biological implications of this observation, they inoculated five different vegetable species with the three mutants corresponding to these strain-specific genes, and they observed significant differences in the response of each host species to infection.
These findings highlight the role of genome dynamics in the evolution of pathogenicity in Xcc in response to different host species.
The study, which represents the largest comparative and functional genomics screen for a plant or animal bacterial pathogen to date, is published online today in the journal Genome Research.
Different forms of black rot can severely affect other aspects food production. Wheat for example is subject to more diseases than other grains, and, in some seasons, especially in wet ones, heavier losses can be sustained, pushing up prices for millers and bakers.
Cocoa production is another industry that can be badly affected, with some estimates putting losses as high as 30 per cent to 40 per cent of global cocoa production. These costs are often absorbed by processors and manufacturers under pressure to keep prices as low as possible.
Black rot can also devastate fruit crops. In 1997, an outbreak of black rot decimated the cantaloupe melon crop in the Rio Grande Valley of Texas, resulting in losses of $15 million.