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Comparative Lesions Analysis Through a Targeted Sequencing Approach
Published on: November 5, 2019
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Multilocus Sequence Analysis Reveals Genetic Diversity in Xanthomonads Associated With Poinsettia Production
W Rockey1, N Potnis1, S Timilsina1
1Department of Plant Pathology, University of Florida, Gainesville 32611.
Plant Disease
|February 1, 2019
Summary
Bacterial leaf spot on poinsettias can be caused by multiple Xanthomonas species, not just Xanthomonas axonopodis pv. poinsettiicola. This study identified three distinct genetic groups of Xanthomonas infecting poinsettias, highlighting the need for broad sanitation practices.
Area of Science:
- Plant Pathology
- Bacteriology
- Molecular Phylogenetics
Background:
- Xanthomonas axonopodis pv. poinsettiicola is traditionally recognized as the primary cause of bacterial leaf spot in poinsettias (Euphorbiaceae).
- Ornamental plants, particularly poinsettias, are susceptible to bacterial leaf spot diseases, impacting production and trade.
- Understanding the diversity of causal agents is crucial for effective disease management in ornamental horticulture.
Purpose of the Study:
- To investigate the genetic diversity and pathogenicity of Xanthomonas strains isolated from poinsettia and related ornamental plants.
- To determine if Xanthomonas axonopodis pv. poinsettiicola is the sole causal agent of bacterial leaf spot on poinsettia.
- To identify potential alternative hosts and reservoirs for Xanthomonas pathogens affecting ornamental crops.
Main Methods:
- Isolation and pathogenicity testing of 67 Xanthomonas strains from poinsettia lesions collected over 64 years.
- Multilocus sequence analysis (MLSA) using six housekeeping genes to determine phylogenetic relationships.
- Comparative virulence assays on poinsettia and geranium (Pelargonium spp.).
Main Results:
- MLSA separated the 67 Xanthomonas strains into three distinct clades, with Clade I containing the X. axonopodis pv. poinsettiicola reference strain.
- Clade II showed closer relation to X. hortorum pv. pelargonii, and Clade III included X. codiaei and strains from zebra plant (Acanthaceae).
- Pathogenicity on poinsettia did not differ significantly among strains from the three clades; strains from all clades infected geranium, albeit less severely than X. hortorum pv. pelargonii.
Conclusions:
- Bacterial leaf spot on poinsettia can be caused by a broader range of Xanthomonas species or pathovars beyond X. axonopodis pv. poinsettiicola.
- Xanthomonas strains infecting poinsettia can also infect other ornamental hosts like geranium and zebra plant, indicating potential inoculum reservoirs.
- Effective management of Xanthomonas leaf spot in poinsettia production necessitates comprehensive sanitation programs targeting multiple ornamental hosts.
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