Why do you get black nematodes when you eat bananas?

Bananas are a southern fruit. The bananas we eat in the north are picked in the south before they are fully ripe. After being preserved and transported to the north, many people like to eat bananas and think that bananas have no seeds. In fact, bananas do have seeds. The small black dots in the center of the banana are the seeds. However, bananas have a kind of root-knot nematode. So why do black threads appear when eating bananas?

Banana root-knot nematode is a highly specialized omnivorous plant pathogenic nematode. Root-knot nematode disease must be effectively prevented by strictly implementing the policy of plant protection with prevention as the main focus and integrated control, focusing on agricultural and physical control measures, and coordinating chemical and biological control.

Banana root-knot nematodes[1] mainly harm banana roots, forming large and small nodules (root knots) on the thin roots. The ends of the thick roots swell into drumstick shapes or long, curved shapes. The roots are few and dark brown in color. In severe cases, the skin rots. By cutting open the diseased roots, white or brown pear-shaped female insects and gelatinous egg sacs filled with eggs can be observed under a microscope. Giant cells form in the infected areas, a large amount of phloem tissue necroses, the xylem is particularly swollen, and the ducts are blocked.

The initial symptoms of the aboveground part are not obvious, generally manifested as yellow leaves and short plants, which seem to be due to lack of water and fertilizer. In severe cases in the later stages, the leaves turn yellow and wither, buds are difficult to produce, the fruits are small, and the plants age prematurely.

Banana root-knot nematodes are caused by parasitism of various nematodes of the genus Meloidogyne, among which the southern root-knot nematodes and the Javan root-knot nematodes are the dominant species and are distributed in all banana producing areas. The host range of banana root-knot nematodes is very wide. In addition to bananas, it also infects many crops such as citrus, watermelon, eggplant, and tomato.

1. Infection cycle: Banana root-knot nematodes overwinter in the soil and diseased roots mainly as eggs, second-instar larvae and females. The second-instar larvae infect the tender roots of bananas and parasitize between the root cortex and the pith, stimulating excessive cell growth and division, causing the formation of root knots of varying sizes on the roots. The larvae develop into 3rd and 4th instar larvae and female and male adults inside the roots. The mature females lay eggs in the gelatinous egg sacs exposed outside the roots. The egg sacs burst when they come into contact with water, and the eggs fall into the soil, becoming a source of reinfection. Diseased seedlings and diseased soil are the main routes of long-distance transmission, water flow is an important medium for short-distance transmission, and diseased fertilizers, farm tools, and human and animal activities are all factors that transmit diseases.

2. Disease conditions: The occurrence and development of banana root-knot nematodes are closely related to soil texture, temperature, humidity, previous crop, banana growth period and the cultivation and management level of the orchard. Generally, the disease is more serious in sandy soil than in clay soil; the disease is more serious when the temperature is 25℃~30℃ and the soil moisture is 40%~60%; the disease is more serious when the previous crops are susceptible crops such as tomatoes, cucumbers, watermelons, etc.; the disease is more serious in the banana seedling stage, the orchard management is extensive, the plants have poor disease resistance and the disease is more serious.

1. Cultivate disease-free seedlings: This is the key link in preventing and controlling banana root-knot nematodes. Using disease-free soil to grow seedlings can reduce the incidence of diseases during the seedling stage and prevent the spread of diseases.

2. Implement crop rotation in seriously diseased banana gardens: For banana gardens with serious diseases, crop rotation with rice and other crops, and rotation between water and land, can reduce the source of diseases and insect pests. When planting bananas, plowing the soil one or two months in advance, turning the soil layer containing nematodes to the surface, and drying it in the sun can reduce the incidence of the disease.

3. Strengthen field management: promptly remove diseased and damaged roots, apply more organic fertilizers and irrigate properly to promote the growth of new roots and enhance the plant's disease resistance.

4. Chemical control: Sprinkle nematicides (Ligensha or Duofu) around the banana seedlings when planting. If nematodes are found during the growing period, they can be treated by irrigation with (Ligensha emulsion).