Virology and Crop Protection Laboratory, Cassava Program, International Center for Tropical Agriculture (CIAT), Recta Cali-Palmira Km 17, Palmira, Colombia.
Facultad de Ingeniería, Diseño y Ciencias Aplicadas, Universidad ICESI, Cali, Colombia.
Sci Rep. 2024 Nov 28;14(1):29648. doi: 10.1038/s41598-024-81142-2.
Cassava frogskin disease (CFSD) emerged in the Americas in the 1970s, but its causal agent has to date remained a mystery. The clonal propagation of cassava, high incidence of mixed infections, unknown alternative hosts, and root symptoms taking two or more crop cycles to develop, have made it difficult to identify the causal agent. Consequently, most studies on CFSD have produced a catalogue of pathogens occurring in affected plants. Using a sentinel approach, we captured single-pathogen infections in fields with high incidence of root symptoms. Eight months after being exposed to CFSD, we detected < 6.9% incidence of root symptoms in sentinel plants. Plants were then propagated and transferred to a screenhouse for a second infection cycle and storage root development. Interestingly, molecular diagnostics did not identify an association with phytoplasma or reovirids-pathogens historically reported in CFSD-infected plants-but indicated that single-infections by torradoviruses were sufficient to cause the disease. Further analysis by high-throughput sequencing confirmed the presence of torradoviruses in symptomatic roots and allowed unveiling the occurrence of a second torradovirus species in farmers' fields in Colombia. These new findings should support early interception of infected planting material, development of cassava seed certification standards, breeding and screening for resistance programs, and ultimately significantly reduce the impact of CFSD in cassava.
木薯蛙皮病（CFSD）于 20 世纪 70 年代出现在美洲，但至今其病原体仍不为人知。木薯的克隆繁殖、混合感染的高发率、未知的替代宿主以及需要两个或更多作物周期才能出现的根症状，使得确定病原体变得困难。因此，大多数关于 CFSD 的研究都列出了在受感染植物中出现的病原体。我们采用哨兵方法，在根症状高发的田间捕捉单一致病菌感染。在接触 CFSD 八个月后，我们在哨兵植物中检测到<6.9%的根症状发生率。然后，植物被繁殖并转移到温室中进行第二次感染周期和贮藏根发育。有趣的是，分子诊断并未发现与植原体或呼肠孤病毒有关——这些病原体在 CFSD 感染的植物中已有报道——但表明单一致病菌感染的 torradoviruses 足以引起该疾病。通过高通量测序的进一步分析证实了症状性根中存在 torradoviruses，并揭示了在哥伦比亚农民田间存在第二种 torradovirus 物种。这些新发现应该支持早期截获受感染的种植材料、开发木薯种子认证标准、培育和筛选抗性计划，最终显著降低 CFSD 在木薯中的影响。
