The objective of this work was to evaluate the population variation dynamics of Candidatus Liberibacter spp. under phosphite applications. The 'Ponkan' tangerines (Citrus reticulata Blanco cv. Ponkan) with symptoms and a high degree of huanglongbing (HLB) severity were used for the test. 'Ponkan' tangerine plants were treated with potassium phosphite leaf applications at a dose of 2.5 L ha-1. Applications frequency was intervals of 25 days with a total of two applications. There was variation in bacterium Candidatus Liberibacter spp. population, depending on the application of phosphite. Phosphites have an indirect action on pathogens control, stimulating the formation of phytoalexins, a natural self-defense substance of plants. Indirect effects of these products were reported in citrus seedlings presenting symptoms of phosphorus deficiency, which when treated with foliar applications of potassium phosphite overcame these symptoms, restoring plant growth. Candidatus Liberibacter spp. population in 'Ponkan' (Citrus reticulata Blanco cv. Ponkan) leaves was reduced and the phosphorus and potassium contents increased with 2.5 L ha-1 of potassium phosphite by means of leaf application.

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