The disease affects most citrus species, causing yellowing of shoots, blotchy and mottled leaves, lopsided and poorly colored fruit and loss of viable seeds. The fruit of diseased trees is hard, misshapen and bitter, and the infected trees die within a few years.
Other than one infected backyard tree found in 2012 in the Southern California community of Hacienda Heights, the disease has not been detected in California. However the citrus psyllid that transmits the bacteria was first found in California in 2008 and has since been identified in San Diego, Imperial, Riverside, San Bernardino, Orange, Los Angeles, Ventura, Santa Barbara, Kern and Tulare counties, resulting in quarantines and restricted areas.
The new study:
In this new study, the researchers studied four categories of healthy and diseased citrus trees, with the goal of better understanding how HLB affects trees physiologically during the very early stages of infection.
"Earlier sequencing of the CaLas bacteria genome showed that there were no toxins or enzymes that would destroy plant cell walls, or specialized secretion systems associated with citrus HLB," Dandekar said.
"Because these factors, which normally accompany plant diseases, were not present, we suspected that the disease was causing metabolic imbalances or interfering with nutrient transport in the infected trees," he said.
The researchers used gene sequencing technology to study the "transcriptome," which is the collection of RNA found in the tree leaves and fruit.
Their analysis confirmed that in infected trees, HLB disease caused starch to accumulate in the leaves, blocking nutrient transport through the phloem and decreasing photosynthesi
|Contact: Pat Bailey|
University of California - Davis