Citrus is one of the most crucial horticultural commodities and renowned worldwide because of wide range of flavors and beneficial aspect. Citrus fruits are significant economically in Mexico. Food and Agriculture Organization (FAO), reported that Mexico produces over two million tons of limes and lemons annually1. But; citrus is facing serious pathogen attacks and Citrus huanglongbing (HLB) is the most destructive diseases of citrus globally. This disease is linked with four phloem-restricted α-proteobacteria, “Candidatus Liberibacter” species2 and among them “Candidatus Liberibacter caribbeanus” (C.Lca) is recently reported in Colombia3. The bacteria are transmitted by at least two insect vectors; the Asian citrus psyllid (ACP) and Trioza erytreae.
Unluckily, still there is no procedure to cope with HLB. Up to now in Mexico, HLB is being managed by controlling vector with chemical insecticides and this method has exhibited the satisfactory outcomes. Well, either seasonal fluctuations in C.Las population are interlinked with ACP populations or not; is still under examination and have varied results. In 2007, Gottwald and team conducted an experiment in Florida and reported large numbers of HLB-positive trees diagnosed between August and January, while the maximum bacterial concentrations were observed in December4. On the contrary, in 2014 research was carried out in Pakistan, which showed that the number of trees diagnosed with HLB was highest in summer, inspite of less C.Las prevaing in the ACP vector population5.
In this regard Jose Abel Lopez-Buenfil and colleagues performed a research to recognize the dynamics of the population of HLB interlinked bacterium C.Lca and its insect vector in Citrus aurantifolia Swingle (Mexican lime). In this experiment, leaf samples were obtained every 2 months for 26 months to quantify bacterial titers and young and mature leaves to evaluate preferential sites of bacterial accumulation. Quantitative real-time PCR was used to assess percentage of living and dead bacterial cells.
Scientists noted lesser bacterial titer at high temperatures in the diseased trees comparing to titers in mild weather, inspite of the elevated number insect vector Diaphorina citri in these circumstances. Seasonal fluctuations in the titers of bacteria in mature leaves were also observed when compared to young leaves. On the other hand, there was absence of any statistical link between any meteorological variable, C.Las concentration and D. citri population. Researchers concluded that regarding management techniques, host tree phenology may be important in addition with vector control. Therefore, assessment of citrus phenology, C.Las concentration, ACP population and environmental factors provides insights into the cyclical, seasonal variations of both the HLB pathogen and its vector. This investigation will definitely aid to develop integrative HLB control strategies to improve quality and yield of citrus fruit.
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17 November, 2019