|ROCKEY, WILL - University Of Florida|
|POTNIS, NEHA - University Of Florida|
|TIMILSINA, SUJAN - University Of Florida|
|JONES, JEFFREY - University Of Florida|
|NORMAN, DAVID - University Of Florida|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2014
Publication Date: 6/26/2015
Citation: Rockey, W., Potnis, N., Hong, J.C., Timilsina, S., Jones, J.B., Norman, D.B. 2015. Multilocus sequence analysis reveals genetic diversity in xanthomonads associated with poinsettia production. Plant Disease. 99(6):874-882. https://doi.org/10.1094/PDIS-08-14-0867-RE.
Interpretive Summary: This study compared various xanthomonads associated with leaf spots on ornamental crops, with emphasis on poinsettia (Euphorbia pulchrimma). It was previously assumed that Xanthomonas axonopodis pv. poinsettiicola was the causal agent of leaf spot on poinsettia, however in this study revealed two other Xanthomonas sp. were able to cause poinsettia leaf spot namely, X. hortorum pv. pelargonii and X. codiaei.
Technical Abstract: Xanthomonas axonopodis pv. poinsettiicola is traditionally identified as the primary causal agent of bacterial leaf spot on poinsettia (Family Euphorbiaceae). Sixty-seven strains of xanthomonads isolated from lesions associated with several species within Euphorbia were collected over a 64 year period. These were compared for pathogenicity on several potential hosts and analyzed by multilocus sequence analysis (MLSA) using six housekeeping genes. The 67 Xanthomonas strains associated with poinsettia production were separated into three distinct clades based on MLSA. The first clade identified contained the X. axonopodis pv. poinsettiicola reference strain (LMG849). A second clade was more closely related to X. hortorum pv. pelargonii and the third clade contained the X. codiaei type strain (LMG8678). This analysis indicates that there may also be other additional closely related pathovars or species of Xanthomonas that can infect poinsettia. Strains from all three clades could not be distinguished by symptoms or virulence on poinsettia plants. Strains capable of infecting geranium were found in all three clades, although the extent of leaf spot formation and number of systemic infections was significantly less than those produced by X. hortorum pv pelargonii strains, typically the main causal agent of bacterial leaf spot on geranium. Clade III contained strains isolated from zebra plant (Aphelandra squarrosa), which is a newly recognized host for X. codiaei and X. axonopodis pv. poinsettiicola.