2011 Annual Report
1a.Objectives (from AD-416)
1. Characterize microbial communities associated with tissue necrosis during the terminal stage of lethal yellowing disease of palms.
2. Determine genetic variability/diversity of phytoplasmas affecting potato and other crops.
The ultimate goal of the project is to gain new knowledge of ecology, niche adaptation and pathogenicity evolution of phytoplasmas, causal agents of economically important plant diseases worldwide.
1b.Approach (from AD-416)
For Objective One, necrotic tissues will be harvested from lethal yellows (LY) disease-affected palm trees and total DNA will be extracted from selected tissues. Microbial populations will be characterized using 454 pyrosequencing technology with primers designed to target V3 and V6 hypervariable regions of bacterial 16S rRNA genes. For Objective Two, total DNA will be extracted from symptomatic tissues of phytoplasma-infected plants, and phytoplasma DNA will be enriched through cesium chloride gradient centrifugation. Phytoplasma genome survey sequencing will be conducted using 454 pyrosequencing technology using coded primers. For both Objectives, the sequence data obtained will be analyzed and annotated using a suite of bioinformatic tools.
The cooperative research was initiated to acquire new knowledge of ecology, niche adaptation and pathogenicity evolution of phytoplasmas, cell wall-less bacteria that cause diseases in ecologically and economically important plants worldwide. Genome survey sequencing and metagenomic sequencing approaches have been used to characterize the population structures of the microbial communities associated with affected tissues of phytoplasma-diseased palm, potato, and other plants, gaining insights into interactions among phytoplasmas, their hosts, and other microbes sharing the same niche, and gaining an understanding of what roles a specific host (plant or insect vector) and the associated microorganisms have in the development of specific phytoplasma populations and the disease induced. In this reporting period, we continued to conduct extensive field studies and collected additional samples from diseased palm trees in Caribbean region and from diseased potato plants, suspected insect vectors, and potential reservoir plants nearby the crop plants in Russia and the State of Texas, U.S.A. From analyses of the samples we have identified several previously undescribed phytoplasmas, some of which represent new genetic lineages. Our results revealed a great breadth of genetic diversity among phytoplasmas infecting palm and potato plants. Signs of inter-lineage recombination have been detected within phytoplasma populations present in suspected vectors of Russian potato purple top disease. New primers and adaptors for metagenomic sequencing and phytoplasma genome survey sequencing were designed and synthesized. This project was monitored by conference calls, regularly scheduled meetings, and exchanges of ideas, materials, and data.