Molecular Pathogens, 2025, Vol.16, No.3, 87-99 http://microbescipublisher.com/index.php/mp 90 can distinguish the differences between different specialized types of Fusarium oxysporum (such as the physiological subtypes of sweet potato and tobacco) (Bilgili et al., 2023). 3 Disease Occurrence and Influencing Factors 3.1 Seasonal patterns and environmental conditions Sweet potato root rot is closely linked to environmental conditions. The disease tends to appear more often in warm and humid weather, especially during the summer and autumn growing seasons. High temperatures help the fungi that cause the disease grow and infect the plants. Studies have found that F. solani can live and cause disease in a wide temperature range from 8.5 °C to 34 °C, with the best growth and infection rates around 25 °C~30 °C (Arie, 2019). During hot weather, soil temperature rises, and sweet potato roots become more likely to be infected. Wet soil makes things worse. If it rains for many days, the soil stays too wet and lacks air. This weakens the roots, making it easier for fungi to attack and cause the roots to rot. In drier and better-aerated soil, the disease occurs less often. The weather at harvest time also matters. If sweet potatoes are harvested in cold and wet conditions, their skins may get damaged and not heal well (Lee et al., 2019). This increases the chance of rot during storage. Researchers have shown that wounds made during harvesting are common starting points for infection, especially if the sweet potatoes are not cured properly before storage. Proper storage can help slow down the disease. Keeping sweet potatoes at 13 °C~16 °C and about 85% humidity for curing helps wounds to heal and stops fungi from entering. On the other hand, if stored at 25 °C~30 °C and above 90% humidity, rot can spread fast, with symptoms appearing in 6~8 weeks. 3.2 Variety resistance and cultivation practices Different sweet potato varieties show varying levels of resistance to root rot. Field observations and experiments have shown that some varieties are more resistant than others. For example, a study in Korea tested 21 varieties. One called "Pungwanmi" showed strong resistance to F. oxysporum, while another called "Annobeni" was highly susceptible. Currently, resistance to root rot is considered a complex trait. It is controlled by many genes, not just one. This makes breeding resistant varieties more difficult. Breeders often need to combine different genes and use field screening to find resistant types. Balancing disease resistance with good yield and quality is also important. Some local varieties have high yields but poor resistance, while some wild or landrace varieties resist disease well but don't produce as much (Sugri et al., 2020). So, breeding programs need to find a good middle ground. In recent years, new techniques like genome-wide association studies (GWAS) have helped scientists find specific genes linked to resistance. For example, a Korean study using 96 sweet potato lines found two important genetic markers related to resistance against F. solani. These discoveries can help in developing new resistant varieties using molecular tools. Besides variety resistance, farming practices also affect disease levels. One key step is starting with healthy seed roots or vine cuttings. Both F. oxysporum and F. solani can spread through infected planting material. Before planting, diseased roots or vines should be removed carefully. Studies have found that F. solani can produce many thick-walled spores on infected roots. These spores can stick to vines and spread the disease in the field. That’s why it is best to use cuttings taken at least 2 cm~3 cm above the soil and avoid pulling up vines with soil attached. Crop rotation is another useful method. When sweet potatoes are planted in the same field year after year, disease often gets worse. But rotating with crops like corn or wheat can reduce the risk. Other practices like proper spacing and using raised beds help control the disease by improving air flow and soil drainage (Yan et al., 2022). Research suggests that raised beds can lower the chance of infection by making soil conditions less favorable for the fungi. Fertilization also matters. Using enough potassium helps sweet potato roots stay strong and resist disease. But using too much nitrogen can cause the plants to grow weak vines and become more likely to get infected.
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