LIBRO-CONGRESO-CITRUS

S12
for this disease, we started the characterization of some essential biological processes of Xcc, among them
chromosome segregation, in an attempt to identify targets to which we could develop antimicrobials. Here,
we describe the effects of ParB disruption in Xcc, a well conserved factor in bacteria that has no homologues
in derived eukaryotes. ParB, together with its partner ParA, is responsible in several other organisms for
the proper segregation of the genetic material. Using phase contrast microscopy we show that Xcc mutants
disrupted for parB (Xcc parB::pAPU2) form filaments, which is consistent with a chromosome segregation/
cell division defect. Surprisingly, we found that these cells also lost the ability to colonize the susceptible host
Rangpur lime. ParB has been implicated with bacterial motility and divisional septum placement; however,
our results are the first to report on the involvement of the chromosome segregation protein ParB with
virulence.
S12P28
Analysis of microRNAs involved in defense response signaling against Xanthomonas spp. in Citrus limon
Chiesa M.A. 1 , Torres P.S. 2 , Campos L. 3 , Roeschlin R.A. 1 , Gerhardt N. 1 , Filippone M.P. 4 , Conejero V. 3 , Castagnaro A.P. 4 ,
Vojnov A.A. 2 , Gmitter Jr. F.G. 5 , Gadea J. 3 , and Marano M.R. 1
1Instituto de Biologia Molecular de Rosario-CONICET (IBR), Argentina; 2Fundación Pablo Cassará-Buenos Aires, Argentina; 3Instituto de Biologia Molecular y Celular de Plantas (IBMCP), Universidad Politecnica de Valencia-CSIC, Spain; 4Estacion Experimental Obispo
Colombres (EEAOC-Tucuman), Argentina; and 5University of Florida (IFAS), Citrus Research and Education Center Lake Alfred, U.S.A..
jgadeav@ibmcp.upv.es
MicroRNAs (miRNAs) are small conserved noncoding RNAs of ~ 22 nt long that are present in most eukaryotic
genomes. They play a fundamental role as negative regulators of target genes, which are involved in different
signaling pathways of biological processes, such as development, hormone signaling and response to
biotic and abiotic stresses. Citrus spp. is severely afflicted by Asiatic Citrus Bacterial Canker (CBC), a disease
caused by Xanthomonas citri subsp. citri (XC). To get insight into the plant defense responses that could
ameliorate canker development, we studied C. limon miRNAs expression in the interaction with a highly
virulent strain (XC), a non-pathogen strain of citrus (X. campestris pv. campestris, Xcc) and a strain that
generates a hypersensitive response (X. fuscans pv aurantiifoli strain C, Xfa-C). The obtained results revealed
interesting expression patterns for some of the miRNAs involved in hormone signaling pathways (miR159,
miR160, miR167, miR393), oxidative stress (miR398) and cell-wall strengthening (miR408). These miRNAs
are presumably regulating target genes involved in signalling pathways important for C. limon resistance. The
biological significance of the differential expression of the assayed miRNAs in compatible, incompatible and
non-pathogenic interactions is discussed.
S12P29
Influence of different copper hydroxide spray volumes and doses to control Citrus Canker in
lemon in Tucumán, Argentina
Salas López H. 1 , Mansilla C. 2 , Stein B. 1 , Rojas A. 1 , and Figueroa D. 1
1Estación Experimental Obispo Colombres (EEAOC), Fruticultura, Argentina; and 2CITRUSVIL, Argentina. hsalas@eeaoc.org.ar
Citrus Canker caused by Xanthomonas citri subsp. citri is one of the most important citrus diseases. Three
volumes (high, medium and low: 10000, 5000 and 2000l/ha, respectively) and two doses (15 and 7.5 Kg/ha of
commercial product) of copper hydroxide (53.8%) bactericides were evaluated in lemons. A trial was conducted
throughout three consecutive crop seasons in a commercial grove (Limoneira 8 A Lisbon/Swingle citrumelo)
planted with 250 trees/ha density in 1997. A randomized complete block design with four replicates and six
treatments was considered: 1) high volume-high dose (traditionally used); 2) medium volume-high dose; 3)
low volume-high dose; 4) medium volume-low dose; 5) low volume-low dose and 6) untreated. Monthly sprays
from October to January were performed in each season and canker incidence on fruit was estimated at harvest.
Regardless of the volume and dose, copper significantly decreased canker incidence on fruit with a considerable
decrease as the year elapsed. The highest incidence was recorded in untreated trees (91% of infested fruit) and
the lowest (7%) in copper-treated trees. Differences among treatments were not significant in years with low
210 - VALENCIA CONFERENCE CENTER, 18th-23rd NOVEMBER 2012