Translocação de Candidatus Liberibacter asiaticus em citros
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Data
2017-01-30
Autores
Raiol Júnior, Laudecir Lemos [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Huanglongbing (HLB), causada pela bactéria Candidatus Liberibacter asiaticus (Las) que coloniza o floema das plantas cítricas, é considerada a doença mais grave e destrutiva dos citros. Aspectos da patogenicidade de Las ainda não estão compreendidos, dificultado pela condição não cultivável do patógeno. Entender como Las se movimenta internamente na planta para colonizar os diferentes tecidos é fundamental para o controle do HLB e a busca de materiais com potencial de resistência. O objetivo desse trabalho foi caracterizar a movimentação de Las em plantas de citros. Nos experimentos plantas de laranjeiras foram inoculadas por enxertia de segmentos de ramos de plantas infectadas de 2 - 3 cm de comprimento. Para estudo da velocidade de movimentação de Las nos vasos do floema, foi utilizado duas metodologias. A primeira envolveu poda sequencial do caule a diferentes distâncias do ponto de inoculação e avaliação de amostras de folhas seis meses após a inoculação. Já na segunda metodologia foi realizado a coleta de amostras de anéis de casca do caule a diferentes distâncias do ponto de inoculação e de raízes fibrosas. Foi avaliado também a influência de novos fluxos de crescimentos na movimentação de Las. Lotes de plantas foram podadas na parte aérea ou no sistema radicular para indução do crescimento. Plantas não podadas foram usadas como controle. Foram amostradas folhas que surgiram na planta após a inoculação, folhas velhas, anel de casca e raízes fibrosas a partir de 15 dias após a inoculação. E para o estudo do padrão de movimentação de Las nas plantas, foram utilizadas plantas aneladas totalmente, parcialmente e não aneladas no caule e inoculadas no topo ou na base do caule para avaliar se Las precisa passar pela raiz para colonizar outros pontos da copa. Os resultados permitiram concluir que a velocidade média necessária para Las atingir a raiz de 95% das plantas, localizada 85 cm abaixo do local de inoculação, foi estimado variando entre 2,9 a 6,9 cm dia-1. Foi observado também que fatores ambientais influenciam a velocidade de movimentação da bactéria na planta. No experimento para avaliar a influência das regiões de crescimento, parte aérea ou sistema radicular, na movimentação de Las, a maior probabilidade de detecção da bactéria foi observada em tecidos das regiões que foram estimulados a crescer através da poda, quando comparados com as plantas não podadas. Com relação aos tecidos amostrados, anéis de casca do caule foram as que apresentaram maiores porcentagens de detecção de Las. Além disso, as plantas em que foram estimulados o crescimento do sistema radicular apresentaram 90% a mais de probabilidade de se encontrar Las nas raízes em relação a amostras de casca do caule ou folhas. Os resultados sugerem que a bactéria precisa passar pela raiz para atingir outros pontos da copa. No entanto, esse fator não foi totalmente esclarecido porque o anelamento das plantas provocou acúmulo de amido e alteração no fluxo da seiva, que pode ter influenciado na movimentação da bactéria.
Huanglongbing (HLB), caused by the bacteria Candidatus Liberibacter asiaticus (Las) which colonizes the phloem of citrus plants, is considered the most serious and destructive disease of citrus. Las pathogenicity aspects are not yet understood, hampered by non-cultured condition of the pathogen. Understanding how Las moves within the plant to colonize the different tissues is fundamental for HLB management and searching for materials with resistance potential. The objective of this research was to characterize the movement of Las in citrus plants. In the experiments orange plants were inoculated using grafting segments from infected plant branches 2-3 cm long. To study the speed of Las movement in phloem, two methodologies were used. The first involved sequential pruning of the stem at different distances from the inoculation site and evaluation of leaf samples six months after inoculation. In the second methodology was collected the ring samples of stem bark at different distances from the point of inoculation until the ground level and fibrous roots. It was also evaluated the influence of the growth flows in the Las movement. Lots of plants were pruned in the aerial part or in the root system to induction of growth. Unpruned plants were used as controls. The plants were evaluated by sampling young leaves, mature leaves, stem bark and roots every 15 days from inoculation. For the study of the movement pattern of Las in the plants, we used totally, partially and non-girdling plants and inoculated at the top or base of the stem to evaluate if Las must pass through the root to colonize other points of the canopy. The results allowed to conclude that the average speed required for Las to reach the 95% root of the plants, located 85 cm below the inoculation site, was estimated varying from 2.9 to 6.9 cm day-1. It was also observed that environmental factors influence the speed of the bacterium movement in the plant. In the experiment to evaluate the influence of the growth regions, aerial part or root system, in the movement of Las, the highest probability of detection of the bacteria were observed in tissues from the regions that were stimulated to grow through pruning, when compared with unpruned plants. Regarding the sampled tissues, stem bark rings were the ones with the highest percentages of Las detection. Furthermore, the growth of the root system increased the possibility of finding Las in roots samples by 90% than in other sampled tissues. The results suggest that the bacteria must pass through the root to reach other parts of the canopy. However, this factor was not fully understood because the plants girdling caused starch accumulation and change in the sap flow, which may have influenced the movement of the bacteria.
Huanglongbing (HLB), caused by the bacteria Candidatus Liberibacter asiaticus (Las) which colonizes the phloem of citrus plants, is considered the most serious and destructive disease of citrus. Las pathogenicity aspects are not yet understood, hampered by non-cultured condition of the pathogen. Understanding how Las moves within the plant to colonize the different tissues is fundamental for HLB management and searching for materials with resistance potential. The objective of this research was to characterize the movement of Las in citrus plants. In the experiments orange plants were inoculated using grafting segments from infected plant branches 2-3 cm long. To study the speed of Las movement in phloem, two methodologies were used. The first involved sequential pruning of the stem at different distances from the inoculation site and evaluation of leaf samples six months after inoculation. In the second methodology was collected the ring samples of stem bark at different distances from the point of inoculation until the ground level and fibrous roots. It was also evaluated the influence of the growth flows in the Las movement. Lots of plants were pruned in the aerial part or in the root system to induction of growth. Unpruned plants were used as controls. The plants were evaluated by sampling young leaves, mature leaves, stem bark and roots every 15 days from inoculation. For the study of the movement pattern of Las in the plants, we used totally, partially and non-girdling plants and inoculated at the top or base of the stem to evaluate if Las must pass through the root to colonize other points of the canopy. The results allowed to conclude that the average speed required for Las to reach the 95% root of the plants, located 85 cm below the inoculation site, was estimated varying from 2.9 to 6.9 cm day-1. It was also observed that environmental factors influence the speed of the bacterium movement in the plant. In the experiment to evaluate the influence of the growth regions, aerial part or root system, in the movement of Las, the highest probability of detection of the bacteria were observed in tissues from the regions that were stimulated to grow through pruning, when compared with unpruned plants. Regarding the sampled tissues, stem bark rings were the ones with the highest percentages of Las detection. Furthermore, the growth of the root system increased the possibility of finding Las in roots samples by 90% than in other sampled tissues. The results suggest that the bacteria must pass through the root to reach other parts of the canopy. However, this factor was not fully understood because the plants girdling caused starch accumulation and change in the sap flow, which may have influenced the movement of the bacteria.
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Palavras-chave
Citrus spp., Huanglongbing, Movimentação, qPCR, Floema, Movement, Phloem