Soybean Viral Disease: Symptoms, Causes, and Control Measures Explained

During the growth of soybean, several viral diseases can occur, and these diseases can seriously affect its growth. Soybean viral disease is a systemic disease with a very wide distribution, commonly occurring in all major soybean-producing areas. Below, let us take a look at the symptoms, causes, and control measures of soybean viral disease.

I. Symptoms of soybean viral disease

1. Mild mosaic type

The leaves are flat and spread out, with pale yellow mottling visible to the naked eye. When diseased leaves are picked and held up to sunlight, alternating yellow and green mottling can be seen. Plant growth is basically normal. Resistant varieties and plants infected late in the season mostly show this symptom.

2. Crinkled-leaf mosaic type

The leaves are crinkled and twisted, with blister-like protrusions along the veins. The plants are stunted and bear few pods.

3. Severe mosaic type

The diseased leaves show alternating yellow and green mosaic patterns, with severe crinkling, protruding mesophyll, leaf margins curling backward, vein necrosis, and stunted, dark green plants.

4. Yellow spot type

It generally occurs mixed with mild mosaic and crinkled mosaic symptoms. This condition has two phenotypes: one is yellow spot necrosis, mostly seen in various parts of southern China, and the other is Northeast yellow spot mosaic. Both phenotypes are mostly seen at the pod-setting stage. In the former, the leaves on the plant are crinkled with yellow mottling, and the veins turn brown and necrotic. Generally, the old leaves do not crinkle, but the upper leaves of the plant mostly appear crinkled and mosaic-like.

5. Bud blight type

The stem tips and terminal buds of the lateral branches of diseased plants turn reddish brown or brown, shrivel and curl, and finally die back in dark brown. The plants are stunted, and the stems break easily. Symptoms at the flowering stage mostly show wilted flower buds that do not set pods. Symptoms at the pod-setting stage are round or irregular brown patches on the pods, and the pods mostly become deformed.

6. Brown spot type

It varies depending on the color of the seed hilum. Seeds with a brown hilum show brown mottling, those with a yellow-white hilum show light brown, and those with a black hilum show black.

II. Causes of soybean viral disease

In hot, dry weather conditions, on plots where undecomposed farmyard manure is used, on late-planted plots, on plots with young seedlings, on plots with insufficient water and fertilizer during the fruit expansion period, on plots with excessive nitrogen fertilizer application, on poor and infertile plots, on compacted plots, and on plots with heavy clay soil, soybean plants have poor physiological resistance, viral disease occurs more severely, and yield reductions are greater.

III. Control measures for soybean viral disease

1. Agricultural measures

Strictly select seeds before sowing and remove brown-spotted seeds. Sow at the appropriate time so that soybean flowers before the peak period of planthopper outbreaks. Remove diseased seedlings at the seedling stage, promptly control white planthoppers, strengthen field management, cultivate strong seedlings, and improve the disease resistance of the variety.

2. Breeding and promoting virus-resistant varieties

Because soybean mosaic virus is mainly spread through seeds, and disease resistance differs greatly among varieties, and because the physiological races of mosaic virus differ from place to place, the same variety grown in different regions also differs in disease resistance. Therefore, virus-resistant varieties should be bred and promoted on the basis of clarifying the main physiological races of mosaic virus in the region.

3. Establish disease-free seed fields

Many viruses infecting soybean are spread through seeds. Therefore, planting virus-free seeds is one of the most effective control approaches. Two points should be noted when establishing virus-free seed fields: first, there should be no virus host plants within a 100-meter radius around the seed field; second, after the seedlings emerge in the seed field, diseased plants should be removed promptly, and diseased plants should be pulled out once more before flowering. After 3-4 years of planting, virus-free seed sources can be obtained. The seed transmission rate of first-grade seeds is below 0.1%, and the seed transmission rate of commercial seeds (field planting seeds) is below 1%.