Sweet potato as a phytosanitary object

The primary pathogens include viruses from the Potyvirus, Geminivirus, and Carlavirus groups. These pathogens can persist systemically within the tubers, making the crop a major source of infection.

Fungal pathogens associated with sweet potatoes include causal agents of Fusarium wilt and various types of root rot. These organisms can survive in soil and crop debris for extended periods.

Bacterial pathogens, such as Streptomyces ipomoeae, cause sweet potato scurf and other tuber diseases, significantly impacting marketability and plant vigor.

Because the crop is propagated vegetatively, pathogens are easily multiplied and spread across fields. This makes the selection of clean planting material the most critical aspect of management.

Sweet potato acts as a source of infection for a wide range of vegetable crops. Vectors like aphids and whiteflies frequently move from sweet potato fields to neighboring crops, transmitting viral loads.

Infested planting material often results in yield losses of 50–80%. Viral infections suppress physiological processes, leading to leaf deformation, chlorosis, and stunted plant growth.

Synergistic viral infections are common in sweet potatoes, where multiple viruses interact to cause severe damage, often resulting in the death of growing tips and complete crop failure.

Fungal pathogens carried by sweet potatoes can contaminate soil, restricting the production of susceptible vegetables for several seasons due to the buildup of inoculum.

The economic impact includes both reduced field yield and post-harvest storage losses. Infected tubers are prone to rapid decay and secondary infections, leading to significant loss of product quality.

The infection cycle intensifies during the growing season as insect vectors become active. Warm summer temperatures favor the rapid movement and feeding of vectors, spreading viruses within the crop.

During the storage period, pathogens continue to develop if environmental conditions are not strictly managed. High humidity and poor ventilation in storage facilities trigger fungal and bacterial rot.

The planting season is a critical risk period. Using infected "mother" roots ensures that the virus is distributed throughout the field from the very start of the growth cycle.

Fungal pathogen spread is most active during periods of high soil moisture, which often occurs at the beginning of the season or during heavy rainfall, facilitating the infection of roots.

Pathogen life cycles are tightly integrated with the crop's phenology. Plant stress caused by abiotic factors lowers natural resistance, allowing pathogens to rapidly colonize healthy plant tissue.

Typical viral symptoms include mosaic patterns on leaves, chlorosis, and leaf curling. The plants often appear stunted, and photosynthesis is significantly reduced due to structural changes.

Fungal rot symptoms appear as dark, sunken spots on the tuber surface. Upon cutting, one might observe discolored flesh and necrotic areas that spread from the center of the infection.

Fusarium wilt is characterized by yellowing of the foliage and premature wilting despite sufficient soil moisture. Cross-sections of the stem reveal browning of the vascular tissues.

Bacterial scurf manifests as dry, scabby lesions on the tuber skin. These wounds often become entry points for secondary saprophytic organisms that cause soft rot.

• Interveinal yellowing of leaf blades.
• Presence of dark, sunken lesions on tuber skins.
• Premature drooping and wilting of vines.
• Deformation of new shoots and leaves.

The primary control measure is the use of virus-free planting material produced through tissue culture (in vitro) propagation. This is the only reliable way to break the disease transmission cycle.

Strict adherence to quarantine regulations for the movement of sweet potato tubers is essential to prevent the introduction of new viral strains or exotic pathogens into new regions.

Integrated pest management (IPM) to control insect vectors using insecticides and physical barriers is crucial to keep viral pressure below economic thresholds.

Crop rotation of at least 3-4 years helps reduce the soil-borne inoculum of fungal pathogens. Thorough removal and destruction of crop residues are necessary to minimize sources of infection.

Post-harvest hygiene, including proper drying and storage at optimal temperatures and humidity, is vital to prevent the spread of rot. Fungicide treatments before storage may provide additional protection.