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ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Publications at this Location » Publication #321294
Title: Seasonal variation in populations of ‘Candidatus Liberibacter asiaticus’ in citrus trees in Paraná state, Brazil

Author
item SAUER, ALINE - University Of Maringa
item ZANUTTO, CARLOS - University Of Maringa
item NOCCHI, PAULA - University Of Maringa
item MACHADO, MARCOS - Agronomical Institute Of Campinas (IAC)
item Bock, Clive
item NUNES, WILLIAM - University Of Maringa

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2015
Publication Date: 8/1/2015
Citation: Sauer, A.V., Zanutto, C.A., Nocchi, P.T., Machado, M.A., Bock, C.H., Nunes, W.M. 2015. Seasonal variation in populations of ‘Candidatus Liberibacter asiaticus’ in citrus trees in Paraná state, Brazil. Plant Disease. 99:1125-1132.

Interpretive Summary: Huanglongbing (HLB) is considered one of the most destructive diseases of citrus. The objective of this study was to evaluate seasonal variation of the in planta population of ‘Ca. Liberibacter asiaticus’ (Las) in the foliage of citrus trees in Brazil using real-time PCR. The bacterial population in the plants was tested on a monthly basis for up to 20 months. The Las titers were analyzed and significant differences were observed in values between seasons. Autumn had the highest Las titer, and is thus considered the best period to detect Las infection in citrus plants in southern Brazil. Concomitant with the increase of the bacterial population in the host, there was an increase in severity of HLB symptoms in the trees over time. The results identify the optimal season to sample foliage for Las in southern Brazil (autumn) and confirm the importance of sample timing to maximize detection of Las and thus contribute to the search for effective measures to manage HLB.

Technical Abstract: Huanglongbing (HLB) is considered one of the most destructive diseases of citrus as the plants rapidly become unproductive, enter a decline and eventually die. HLB is caused by the phloem-limited bacterium ‘Candidatus Liberibacter’ spp. The objective of this study was to evaluate seasonal variation of the in planta population of ‘Ca. Liberibacter asiaticus’ (Las) in in the foliage of citrus trees in Brazil using real-time PCR (qPCR). Eleven plants (naturally infected, then screened) in the field with very mild and localized symptoms of HLB were confirmed Las-infected by conventional PCR, and the canopies were divided into four quadrants. The bacterial population in the plants was tested on a monthly basis for up to 20 months by quantifying Las DNA using qPCR Las-specific primers (As84F/As180R). The average Ct (cycle threshold) values, which relate to Las titer, were analyzed using a mixed model. Significant differences were observed in Ct values between seasons (F = 8.77, P = 0.0004), and abrupt changes were observed in Ct values in different quadrants of the plants. Autumn had the lowest Ct values, indicating the highest Las titer and is thus considered the best period to detect Las infection in citrus plants in southern Brazil. In addition to the seasonal changes in Ct values, there was an initial decline in the Ct value in the months following initial detection, the rate of decline slowing with time. Concomitant with the increase of the bacterial population in the host, there was an increase in severity of HLB symptoms in the trees over time (Spearman’s rank correlation, r = -0.4083, P<0.0001). The results identify the optimal season to sample foliage for Las in southern Brazil (autumn) and confirm the importance of sample timing to maximize detection of Las and thus contribute to the search for effective measures to manage HLB.