potato black shank

Erwinia carotovoravar.atroseptica(Van Hall)Dye.

[Host crops] Solanaceae, cucurbitaceae, legumes, umbelliferae and many other crops.

[Disease diagnosis] It can occur in the whole growth period, mainly damaging rhizomes and tubers. When the seed potato belt is seriously ill, the buds rot before they are unearthed, or the seedlings die soon after they are unearthed; when the disease is mild, the seedlings are 10~20 cm high. The diseased plant is short, yellow and short, the cortex and pith of the underground rhizome turn black, and the water stains rot, so it is called black shank disease. Severe, black part of the extension and mother potato, potato pieces caused by wet soft corruption, issued sour smell. The roots of diseased plants are all destroyed, easily pulled out from the soil, and soon die. Sometimes the disease develops slowly, the diseased plant is hard and straight, the leaf color is gray and green, the leaf margin is reversed, the top leaf has a slight metallic luster, and the diseased plant wilts and dies finally. Longitudinal section of diseased stem, vascular bundle browning; longitudinal section of diseased potato, diseased tissue soft, often forming black holes, a clear black line at the junction of disease and health. When dried, the tuber pedicle ends shrivel and harden. The pathogen is carrot soft rot, stem bacteria black shank disease. The fungus is short rod-shaped, obtuse at both ends, with 4~5 flagella, no spores, negative gram staining reaction. Colonies on agar medium are pale white and round.

The disease is mainly transmitted by seed potatoes with bacteria and invaded by wounds. Cutter-knife infection is the main way of disease transmission during potato cutting. After invasion, the pathogen develops in the intercellular space of seed potato epidermis tissue, enters stem, root and tuber along vascular bundle, secretes pectinase, dissolves the adhesive layer in cell wall, causes cell separation, tissue disintegration and rot. The reinfection of tubers in the field was mainly caused by vector transmission such as flies or nematodes. Temperature and humidity were the main factors affecting disease prevalence. Warm and humid conditions favour bacterial invasion. Poor drainage, excessive irrigation frequency, soil wet cold, weak plants, affect wound healing ability, reduce resistance, the disease is aggravated. After harvest, storage under poor ventilation, high temperature and high humidity is conducive to disease development.