LIBRO-CONGRESO-CITRUS

S12
only occurred in the latter. Taken together at the whole plant level, HLB infection induces fewer and less severe
anatomical changes in rough lemon than in sweet orange. In particular, the absence of obvious changes in
the rough lemon root system is suggested to be critical for sustaining plant growth after infection, and should
greatly contribute to its HLB tolerance.
S12P08
The significance of early root infection in Huanglongbing disease development and crop loss
Johnson E.G., Bright D.B., and Graham J.H.
University of Florida (UF-CREC), Citrus Research and Education Center, USA. egjohnson@ufl.edu
Huanglongbing (HLB) is a systemic disease of citrus caused by the phloem-inhabiting bacterium “Candidatus
Liberibacter asiaticus” (Las). Disease in grove trees is initially identified by foliar symptoms, most commonly
blotchy mottle. Detection of Las in leaf tissue by qPCR early in disease development is usually limited to
symptomatic leaves and proximal young leaves. Over multiple years, disease symptoms and detectable Las
spread to the rest of the canopy. A negative exponential relationship observed between canopy disease severity
and yield decline indicates larger than expected crop loss when symptoms are limited to one or a few branches.
Observations in potted and grove trees revealed that Las is frequently detectable in roots months before
detection of Las in leaves and foliar symptom development. Asymptomatic and recently symptomatic grove
trees with Las detected in root tissue have from 26-46% lower root density compared to apparently healthy
trees. These results suggest that early infection of roots by Las causes root damage before the appearance
of foliar symptoms and is associated with the larger than expected yield reduction on trees with initial foliar
symptoms. Further understanding of the early effects of Las infection on roots and HLB tree decline is needed.
S12P09
Monitoring “Candidatus Liberibacter asiaticus” in a commercial orchard of sweet orange and
‘Tahiti’ lime in the northwest of Paraná State
Sauer A.V. 1 , Nocchi P.T.R. 1 , Zanutto C.A. 1 , Rinald D.A.M.F. 2 , and Nunes W.M.C. 1
1 Universidade Estadual de Maringá (UEM), Nucleo de Pesquisa em Biotecnologia Aplicada (NBA) - Centro de Ciências Agrárias (CCA),
Brazil; and 2 Secretaria de Estado da Agricultura e Abastecimento (SEAB), Brazil. alinevanessasauer@hotmail.com
Huanglongbing (HLB) stands out as one of the most devastating citrus diseases worldwide, affecting several
species of citrus. The symptoms are characterized by branches with yellow leaves, usually isolated in plants.
The objective of this study was to evaluate the population behavior of the bacterium “Candidatus Liberibacter
asiaticus” in a commercial orchard. Plants of sweet orange and ‘Tahiti’ lime naturally infected with HLB were
protected with aphid-proof screens to prevent the spread of disease in the area, after confirmation of diagnosis
by conventional PCR. The bacterial population monitoring was performed by real-time PCR after total DNA
extraction from main veins of symptomatic leaves collected monthly, for twenty months. In each plant, four
samples were collected and analyzed from the quadrants of the tree. In the species studied erratic behavior of
the bacteria were observed. Even after detection in one quadrant of the plant, after a few months it was not
possible to verify the presence of the etiologic agent in the same place. For the sweet oranges, the quadrants
that expressed more severe symptoms, showed the greater amount of bacteria, with the Ct between 18 and 33.
For the ‘Tahiti’ lime similar results to those described for sweet oranges were found. These results contribute to
the study of the epidemiology of HLB in this crop and helps to the search for effective control measures.
S12P10
Multiplication of “Candidatus Liberibacter asiaticus” in Citrus sinensis, Citrus sunki, Poncirus
trifoliata and hybrids obtained from crosses between Citrus sunki and Poncirus trifoliata
Boava L.P., Cristofani-Yaly M., Coletta Filho H.D., Bastianel M., and Machado M.A.
Centro de Citricultura Sylvio Moreira, Instituto Agronômico, Brazil. mbastianel@centrodecitricultura.br
Huanglongbing (HLB) is caused by a phloem-limited bacterium and can be transmitted by both psyllid
vector and graft propagation. “Ca. Liberibacter asiaticus” (Las) is the most widespread specie in Brazil and
202 - VALENCIA CONFERENCE CENTER, 18th-23rd NOVEMBER 2012