Carbohydrate translocation disorder

Carbohydrate translocation disorder is a physiological pathology in plants characterized by the disruption of the transport of synthesized sugars from leaves, where photosynthesis occurs, to the active sinks such as fruits, seeds, and root systems. It is not caused by a specific living organism but is a systemic failure of the plant's internal logistics.

In terms of plant physiology, this condition is classified as a metabolic disorder. While it does not have a taxonomic rank, it is often a critical symptom of systemic plant diseases, particularly those caused by phloem-limited viruses or phytoplasmas that physically obstruct the sieve elements required for the movement of assimilates.

This disorder impacts a wide range of crops including cereals, viticulture, and fruit trees. The visual symptoms involve chlorosis, brittle leaf tissue due to starch accumulation, reduced fruit size, and lack of sugar accumulation. In severe cases, the plant undergoes physiological collapse, significantly reducing the marketability of the produce.

The biology of the condition is driven by environmental and nutritional factors. A deficiency in boron is a classic cause, as boron complexes with sugars to facilitate their crossing through plant cell membranes. Furthermore, extreme heat and drought stress cause the phloem to shrink, preventing the effective translocation of carbon-based nutrients needed for plant development.

Management and control strategies focus on maintaining optimal nutrient availability, especially boron and potassium, which are essential for sugar mobilization. Growers should prioritize the control of phloem-feeding insects like aphids and leafhoppers, and implement irrigation strategies that minimize heat stress during the grain-filling or fruit-ripening stages.