Molecular Pathogens, 2025, Vol.16, No.3, 87-99 http://microbescipublisher.com/index.php/mp 92 plowing and sun drying, water-dry rotation, and planting biological fumigation crops such as mustard can further remove residual pathogens in the soil. In addition, the application of actinomycete microbial agents or organic matter conditioners can help re-establish antagonistic microecological barriers and reduce the risk of root rot. Figure 2 Radial growth of 14 Fusarium oxysporum isolates with respect to temperature and pH of the growth medium. A, B, C, and D, Isolates growing in citrate/phosphate buffer set at pH 4, 5, 6, and 7, respectively. Data represent the mean values of two experiments with four replicate Petri dishes for each treatment combination. (Adopted from Cruz et al., 2019) 4 Symptoms and Diagnosis Methods 4.1 Differences between aboveground and underground symptoms Sweet potato root rot shows different signs in the parts above and below the ground. These signs are related but look different. Above ground, infected plants usually grow poorly and look weak. The leaves start to wilt, especially the older ones. They turn yellow from the tip or edge, then the whole plant looks droopy. This is most clear at noon during hot days. At night or when it’s wet, the plant may recover a little. This “wilt-recover” cycle happens because the fungus damages the roots, making it hard for water to move up the plant. When water is needed most, the plant can’t keep up and wilts. As the disease gets worse, the plant stops growing, new leaves become small, and vines may show brown spots or sores. In the end, the whole plant may die (Wei et al., 2019). Underground symptoms are easier to see. When digging up sick plants, you may find that the roots are discolored or rotting. If the disease is caused by F. oxysporum, the root may show light brown, water-soaked spots that grow into sunken patches. Cutting open the root shows the damage stays in the outer tissues and rarely reaches the woody center. Often, a dark ring can be seen just under the skin, showing where the root is damaged (Cruz et al., 2019). If F. solani causes the infection, the damage goes deeper. The root surface may have round, ring-like spots that start light brown in the center and get darker toward the edges. This kind of rot often begins at the ends of the root and spreads inward, which is why it’s called “end rot.” Cutting the root shows damage reaching deep inside, sometimes forming hollow or cracked dry areas. The inside turns orange to dark brown and becomes soft and crumbly. White fungal threads may grow in these empty spaces. Over time, most of the root tissue breaks down, leaving behind only the shriveled skin and hard remains-this is called “mummification.”
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