Changes in carbohydrate metabolism associated to Candidatus Liberibacter asiaticus infection in Mexican lime (Citrus aurantifolia)

Huanglongbing disease (HLB) has rapidly spread in Mexico mainly affecting the Mexican lime industry (Citrus aurantifolia). Knowledge of the variation of carbohydrate metabolism caused by Candidatus Liberibacter asiaticus (CLas) in citrus fruits has allowed assessing its pathogenicity. Yet, response to the infection associated with the metabolism of sugars in Mexican lime is not characterized. The hypothesis was that the infection by CLas differentially affects carbohydrate metabolism during the pre and post-emergence phase of symptoms in Mexican lime plants. The objective was to characterize the changes in carbohydrate metabolism during the CLas infection progression in Mexican lime in greenhouse conditions. The experimental design was completely randomized with five biological subjects and two technical replications. In plants inoculated with CLas, we observed that starch content significantly increased (p ≤ 0.05) through time, up to four times at 16 months after inoculation (mpi) respect to the control. Confocal microscopy showed starch granules accumulation in vascular bundles and collapsed vascular tissue in inoculated plants. The sucrose content was higher (p≤0.05) in the asymptomatic (4 mpi) and symptomatic (16 mpi) stage and the glucose and fructose content were higher (6.3 and 1.5 times) than in the non-infected plants. Photosystem II efficiency (Fv/Fm = 0.77) in symptomatic plants decreased respect to healthy ones (Fv/Fm = 0.81). These changes could affect field production. This is the first study that quantifies changes in the carbohydrate metabolism in Mexican lime plants and their relation to the disease progression.