What Are The 5 Important Seedling Pathogens Causing Soybean Diseases?

Soybean Diseases?

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Since the pathogens that cause soybean seedling and root disease persist in soil, the term “soilborne disease” is frequently used to describe these conditions. Fungi and nematodes are the sources of soilborne illnesses that harm seedlings and roots. Losses in yield are possible when the prevalence of soilborne illnesses is high, and the environment is conducive to disease development. The correct management of soybean diseases depends on accurate diagnosis and early detection.

Seedling diseases, such as damping off or seedling blight, are brought on by a swarm of fungi that attack young plants and destroy their seeds, roots, and lower stems. Pre-emergence or post-emergence are the two categories used to categorize these illnesses. Pre-emergence seedling disease is a condition that affects seedlings before they break through the soil surface. Post-emergence seedling sickness affects seedlings that get the illness after breaking through the soil surface.

This post intends to help you identify the common pathogens causing soybean diseases by attacking the seedlings and roots.


1. Phytophthora

The oomycete plant pathogen Phytophthora sojae is the culprit behind Phytophthora root and stem rot. When soil conditions are favorable for pathogen development, this water mold may infect seeds, seedlings, and plants at all developmental phases of reproduction. Symptoms typically appear one to two weeks after heavy rains, especially in poorly drained soils.

In moist and warm soil conditions, Phytophthora sojae causes seed decay and post- and pre-emergence damping-off of soybeans. 25 to 30°C is the ideal range for the development of illness. Replanting is frequently necessary for fields with severe seed rot and pre-emergence damping-off. As seedlings emerge from the earth, a pale brown soft rot might appear on the roots or the hypocotyl. The seedlings may perish as the roots and hypocotyls become colonized.

As per U.S. Soy International, soybeans are the main source of soy nutrition. Their environmentally friendly and sustainable planting guidelines can help to prevent these pathogens from affecting the soybean plants.

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2. Pythium

The rotting and death of seedlings and seeds, known as damping-off, may be a catastrophic disease that has a significant economic impact on the production of soybeans. Damping-off primarily affects soybean plants at the seedling stage and before germination. In some states, yield reduction could be up to 30%. As soybean acreage grows, so does the prevalence of illnesses like damping-off that have a negative economic impact.

Pythiums are a family of organisms that resemble fungi (Oomycetes) and are intimately associated with the Phytophthora disease. Soybean roots are frequently observed in combination with several Pythium species. Most of them result in post-emergence or pre-emergence damping-off. Usually, the pre-and post-emergence damping-off are the first signs of Pythium infection in the field. Seeds that do not germinate or completely disintegrate while in the soil are signs of pre-emergence damping-off. The earliest signs of post-emergence damping-off are lesions and discoloration on the roots.

The roots will start to decay and dissolve once they become infected, and the seedling will ultimately collapse due to its decaying root system. Because of the thickness and lignification of the root tissue, older plants get more easily infected than young seedlings, which are more vulnerable to post-emergence damping-off.

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3. Rhizoctonia

Plants and seeds might suffer harm from Rhizoctonia before or after emergence. A hard, sunken lesion or rusty-brown decay on the root or lower stem is recognizable in seedlings and older plants. The infections can girdle the stem, kill or stunt plants, etc.

Rhizoctonia losses occur due to a stand decrease in freshly planted fields, the premature mortality of sick plants, and the generation of smaller seeds. During early summer, wilted or dead seedlings remain dispersed throughout the field or in tiny concentrated regions, indicating the presence of this disease. Rhizoctonia solani can cause root rot, seed rot, and hypocotyl lesions. Damping-off happens when germinating seedlings get infected before they emerge. Sunken reddish-brown lesions appear on the hypocotypes of early seedlings.

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4. Fusarium

Fusarium wilt is a disease complex caused by various Fusarium species found in soil. Approximately ten Fusarium species infect soybeans. Various circumstances may benefit different species; some prefer warm and dry soils, while others prefer cold and moist ones. The host range of each species varies, with some species capable of infecting maize, wheat, and other host plants.

The infection causes the roots and stems from darkening vascular tissue from reddish to brown. Exterior dark to light brown lesions may cover a large portion of a root system but will not extend over the soil line. Fusarium-infected roots frequently exhibit visible red, orange, or white mycelium. Taproot infection can encourage adventitious root development near its soil surface. Fusarium can also destroy lateral roots, but it seldom causes seed rot.


5. Nematode

These are tiny worms digging into the roots of soybeans and injecting unseen foreign chemicals into the plant cells using hypodermic needle-shaped mouthparts. It encourages live plant cells to grow into enormous, hyperactive food producers. They feed as they expand and shapeshift. Bloated female worms engorged with eggs eventually spring from the roots. The eggs can lay latent in soil for up to 10 years before infecting again in the mother’s hardened body. This is the fundamental biology of a common and deadly soybean disease, the soybean cyst nematode (SCN).

Large densities of SCN may result in wide areas of soybean fields with severely stunted, yellow, or dead plants. Moreover, symptoms and lower yields in various SCN-infested fields are sometimes misattributed to poor environmental or cultural factors rather than SCN. This unfortunate error leads to increased SCN populations and worse damage or yield losses in succeeding years.


Final Thoughts

Prevention is a fundamental technique for controlling soybean diseases. Plant a high-quality, preferably certified seed, and treat the seed with fungicide. Proper seedbed preparation, planting depth, and seeding rates are required. Crop rotation with non-legume crops is advisable, as is proper control of fertility, weeds, and insects. Lastly, disease and worm-resistant types should be planted. Including the above concepts, and where they apply, into a soybean production program will aid in preventing disease-related yield losses.