PRO/PL> Xanthomonas leaf blight, onion - USA (GA)

[ProMED-mail]

XANTHOMONAS LEAF BLIGHT, ONION - USA (GEORGIA)
*********************************
A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail is a program of the
International Society for Infectious Diseases
<http://www.isid.org>


Date: 27 June 2003
From: ProMED-mail<promed at promedmail.org>
Source: Amer Phytopathol Soc, DISEASE NOTES [edited]


First Report of a Leaf Blight of Onion Caused by _Xanthomonas_ spp. in Georgia.

FH Sanders, DB Langston Jr., JH Brock, and RD Gitaitis, Department of Plant 
Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 
31793; DE Curry, University of Georgia Cooperative Extension Service, Lyons 
30436; and RL Torrance, University of Georgia Cooperative Extension 
Service, Reidsville 30453. Plant Dis. 87:749, 2003; published on-line as 
D-2003-0409-02N, 2003. Accepted for publication 16 March 2003.

In October of 2001 and 2002, a leaf blight was reported affecting Vidalia 
onion (_Allium cepa_) cvs. Pegasus and Sweet Vidalia, respectively, in one 
field each. Lesions on onion seedlings began as a water-soaked, tip dieback 
that gradually blighted the entire leaf. Symptoms on onion transplants 
appeared as elongated, water-soaked lesions that typically collapsed at the 
point of initial infection.

In both cases, disease was very severe on seedlings, and disease incidence 
was 50 percent or more in both fields. Warm temperatures combined with 
overhead  irrigation and above average rainfall likely enhanced the 
severity and spread of disease. Disease was not detected on more mature 
onions once cool, dry conditions occurred later in the season, and no 
significant economic loss occurred.

Seed was tested from seed lots of the aforementioned cultivars and 
_Xanthomonas_ spp. were not found. Diseased tissue was macerated in 
sterile, phosphate-buffered saline, and 10 microliters of the resulting 
suspension was streaked on nutrient agar plates. Yellow-pigmented, 
gram-negative, rod-shaped bacteria were isolated routinely from diseased 
tissue. Bacteria were catalase-positive, cellulolytic, oxidase-negative, 
amylolytic, proteolytic, and utilized glucose in an oxidative manner.

Analysis of whole cell, fatty acid methyl esters (FAME) using the Microbial 
Identification System (MIS, Sherlock version 3.1; MIDI, Inc., Newark, DE) 
identified four representative strains of the bacterium as a pathovar of 
_Xanthomonas axonopodis_ (similarity indices 0.75 to 0.83). Known 
_Xanthomonas_ spp. from onion from Colorado and Texas (1,2) had similar 
FAME profiles when analyzed by the MIDI system.

Onion plants were grown under greenhouse conditions for 2 months and 
inoculated by injecting the base of a quill with 1.0 ml of bacterial 
suspensions (10 million CFU /ml) of the _Xanthomonas_ sp. isolated from 
Georgia, and negative controls were inoculated with 1 ml of sterile water. 
Disease symptoms developed on plants inoculated with bacterial suspensions 
in 4 to 7 days and _Xanthomonas_ sp. was isolated from the lesions 
produced. Disease symptoms occurred when the same suspension was sprayed on 
onion foliage. No symptoms occurred on plants inoculated with 1 ml of 
sterile water.

To our knowledge, this is the first report of _Xanthomonas_ spp. affecting 
Vidalia onions.

References:
(1) T. Isakeit et al. Plant Dis. 84:201, 2000.
(2) H.F. Schwartz and K. Otto. Plant Dis. 84:922, 2000.

--
ProMED-mail
promed at promedmail.org

[The identity of the pathovar associated with the current outbreak of onion 
leaf blight remains to be determined. Do any of our readers have 
information on this point? Please let me know.

According to plant pathologists at Colorado State University, Xanthomonas 
leaf blight of onion caused by _Xanthomonas campestris_ was first reported 
in Hawaii in 1975 and was subsequently reported as a yield limiting disease 
in Colorado in 2000. Annual yield losses due to the pathogen exceeded 17 
percent in southern Colorado, and entire crop failures have occurred in 
other production areas. Disease management involves use of bactericides. - 
Mod.DH]

[see also:
2002
-----
Xanthomonas leaf blight, onion - USA (CA) 20020227.3641
Xanthomonas leaf blight, onion - USA (CA) 20020306.3696]
.....................mpp/dh


*##########################################################*
ProMED-mail makes every effort to  verify  the reports  that
are  posted,  but  the  accuracy  and  completeness  of  the
information,   and  of  any  statements  or  opinions  based
thereon, are not guaranteed. The reader assumes all risks in
using information posted or archived by  ProMED-mail.   ISID
and  its  associated  service  providers  shall not be  held
responsible for errors or omissions or  held liable for  any
damages incurred as a result of use or reliance upon  posted
or archived material.
************************************************************
Visit ProMED-mail's web site at <http://www.promedmail.org>.
Send  all  items  for   posting  to:   promed at promedmail.org
(NOT to  an  individual moderator).  If you do not give your
full name and  affiliation, it  may  not  be  posted.   Send
commands  to  subscribe/unsubscribe,   get  archives,  help,
etc. to: majordomo at promedmail.org.    For assistance  from a
human  being  send mail to:  owner-majordomo at promedmail.org.
############################################################
############################################################