Symptoms and prevention methods of bitter melon blight

What should I do if blight occurs when planting bitter melon? Here are some solutions:

Symptoms of bitter melon blight

In the seedbed, only a few melon seedlings wilt during the day and recover at night. After several days of repeated changes, the diseased plants wilt and die. It is difficult to distinguish from damping-off disease in the early stage. However, after the disease spreads, the diseased plants do not wilt suddenly, and the diseased parts have ring patterns or not very obvious light brown spider-like mold, which is the mycelium or sclerotium of the pathogen, and the disease progresses slowly, which is different from damping-off disease.

Morphological characteristics of the pathogen of bitter melon damping-off disease

Rhizoctonia solani Kühn AG-4 is a fungus belonging to the subphylum Ascomycota. This fungus is a non-spore-forming filamentous fungus. Its hyphae morphology is very similar to some ascomycetes and basidiomycetes. This fungus has hyphae fusion phenomenon. Before fusion, hyphae often attract each other to form three fusion states: complete fusion, incomplete fusion and contact fusion. More than ten hyphae fusion groups have been discovered and established in my country. Among them, AG-4 is the dominant fungus that causes damping-off diseases of cucumber, wax gourd and corn sheath blight. It is an important fungus. It has a wide range of hosts and causes a variety of crop diseases. The strains of the AG-4 hyphae fusion group are divided into two subgroups, AG-4 HG-I and AG-4 HG-II, according to the morphology of sclerotia and the homology of the nitrogen base sequence of DNA. The former forms dark brown sclerotia on PDA medium, and the latter has 1/3 to 1/2 gray to white-brown sclerotia.

Rhizoctonia solani is divided into three major groups. One group is multinucleate Rhizoctonia solani, with 3 or more nuclei, and relatively large hyphae, about 6 to 10 microns in diameter. Its sexual state is Thanatephorus cucumeris (Frank) Donk. A thin layer of waxy or white-pink reticular to reticulate hymenium is formed in the soil. The resulting basidia are barrel-shaped to sub-cylindrical, slightly wider than the hyphae supporting the basidia. The basidia have 3 to 5 peduncles, on which basidiospores are born; the basidiospores are elliptical to broad rod-shaped, with a wider base, 7.5 to 12 × 4.5 to 5.5 microns in size, and the basidiospores can germinate repeatedly, forming 2 basidia on the basidia. Rhizoctonia solani is formed by dense branches at the tip of a single hyphae or by dense branches at the tip and hyphae to form a hyphae knot. Different hyphae fusion groups are not completely the same in terms of morphology, pathology, physiology and ecology. As for the pathogenic specificity of each fusion group and the intrinsic connection between them. [2]

Transmission routes and conditions of disease onset

The mycelium or sclerotium overwinters in the soil and can be saprophytic in the soil for 2 to 3 years. The mycelium can directly invade the host and spread through water flow and agricultural tools. The optimal temperature for the development of the pathogen is 24℃, the highest is 40-42℃, the lowest is 13-15℃, and the optimal pH is 3-9.5. Over-dense sowing, untimely thinning, and high temperature can easily induce the disease.

Prevention and control methods of bitter melon blight

Basic Methods

(1) Selecting heat-resistant varieties such as Jiangmen Dading, Penang Bitter Melon, Suixin No. 2, Xiafeng No. 2, 90-2 Bitter Melon, Zhanyou Bitter Melon, and Yuxi Bitter Melon can reduce the incidence of disease.

(2) Selecting cold-resistant varieties such as Chengdu Dabai bitter melon, Hunan 89-1 bitter melon, 89-3 bitter melon, and high temperature and high humidity resistant varieties such as Jiangmen Dading, Yingyin bitter melon, and Xialei bitter melon can reduce the incidence of disease.

(3) Sow at the right time. Bitter melon likes warmth and can only grow normally when the temperature is above 10℃. Therefore, the sowing time should not be too early. In the north, it is best to sow in the greenhouse in early April. The seedling period is 20 to 30 days.

(4) The seed coat of bitter melon is thick and hard, making it difficult for seedlings to emerge under low temperature conditions in early spring. The uniformity is poor and they are susceptible to disease after being in the soil for a long time. Therefore, mechanical damage should be used before sowing. Use pliers to crack the seed coat, but do not remove it. This will significantly enhance the germination potential.

Pharmaceutical Method

(1) Soak the seeds in 50% hydrogen peroxide for 3 hours, then rinse with clean water and sow. It is suitable for large-scale application.

(2) Before sowing, soak the seeds in warm water at 56°C until they cool naturally to room temperature, then continue soaking for 24 hours. Then place them at 30-32°C for germination. Sow the seeds when the buds are 3 mm long.

(3) To cultivate strong seedlings and prevent damping-off disease, a layer of nutrient soil should be covered after sowing. After sufficient watering, cover with film to keep warm and moisturize. After the seedlings emerge, spray 0.2% to 0.3% potassium dihydrogen phosphate 2 to 3 times to enhance disease resistance.

(4) If necessary, spray 1000-1200 times diluted 69% Anke manganese zinc water dispersible granules or wettable powder.