Occurrence Patterns and Control Methods of Potato Blackleg

Symptoms

Potato blackleg is a bacterial disease that infects vascular bundle tissue and can infect potato stems and tubers. It can occur from seed potato sprouting to the late growth stage, and is most prevalent at the seedling stage. Most diseased plants lose water and droop, the leaf color remains unchanged, the whole plant wilts, and the blackleg portion is mostly softened and rotted. The color of the diseased part is yellowish-brown, light brown, dark brown, or pale green. The vascular bundles inside the stem and the vascular bundles of the underground stem basically become discolored in a ring shape. The junction of the stem base and the mother tuber first turns black, then spreads toward the area near the soil surface, forming blackleg. When humidity is high, the blackleg can rise to 3.3-6.6 cm above the soil surface, and some surfaces have bacterial ooze. At the adult plant stage, blackleg mostly appears dark brown to ink-black, and the pith of the underground stem often becomes hollow. The pathogenic bacteria can spread along the stolon toward the newly formed tubers, and the blackleg symptoms also develop toward the new tubers, causing the navel end to turn dark brown. In severely diseased tubers, the skin becomes dull and lusterless. Lightly infected tubers show no obvious difference from healthy tubers.

Pathogen The potato blackleg pathogen belongs to the genus Erwinia, and the bacterial cells are short rod-shaped. The pathogen has a relatively wide temperature adaptation range and can grow well within 10-38°C, with 25-27°C being optimal, while at 45°C it loses viability.

Occurrence pattern: This disease is mainly carried by diseased tubers. The bacteria are transmitted to seed potatoes through cutting knives, causing the mother tuber to rot, and then enter the aboveground stems of the plant from the mother tuber through the vascular bundles and pith. Later, the pathogen is transmitted from the aboveground stems through the stolons to the newly formed tubers. During storage, when diseased and healthy tubers contact each other, the pathogen can spread through wounds or lenticels, and spreads quickly. Diseased tubers and diseased plant residues left in the soil are also sources of primary infection. Diseased plants in the field can be transmitted by insects and flowing water, and can re-infect healthy plants through wounds.

The occurrence of blackleg is extremely closely related to temperature; disease is severe in areas with abundant rain and low-lying land. During storage and when ventilation in the cellar is poor, with high temperature and high humidity, the pathogen spreads quickly through wounds and lenticels, easily causing cellar rot.

Control Measures

1. Select disease-resistant varieties. Breed disease-resistant varieties from some of the more disease-resistant or disease-tolerant varieties in various regions.

2. Establish disease-free seed fields. Use individual plant selection of superior plants, sprout planting, or whole-tuber sowing.

3. Promote sprouting and sun the seed, and eliminate diseased tubers. Soil trench film sprouting and sunning can be used. The specific method is: about 25 days before sowing, dig a soil trench 0.5 m deep and 1.0-1.3 m wide, with the length determined by the number of seed potatoes. Spread grass 10.0-13.3 cm thick on the bottom of the trench, pile 3-4 layers of seed potatoes on top, cover with plastic film, and keep at 17-25°C for about 7 days to promote sprouting. When the young sprouts grow to the size of a match head, uncover the film during the day to sun the seed, and cover with straw curtains at night to prevent freezing. The navel end can be cut open for inspection to thoroughly eliminate diseased tubers.

4. Mixing with plant ash can promote wound suberization; sow immediately after mixing.

5. Dig out diseased plants, clear diseased residues from the field, practice reasonable crop rotation, and avoid continuous cropping.

6. Sow early at the appropriate time, pay attention to drainage, reduce soil moisture, choose fields with high, dry terrain and good drainage, increase soil temperature, promote early emergence, and reduce infection and spread of blackleg.

7. Field chemical control. Spraying the foliage with 0.1% copper sulfate solution or copper hydroxide, copper hydroxide can significantly reduce blackleg.