Cassava brown streak disease (CBSD), caused by cassava brown streak virus (CBSV) and; Ugandan cassava brown streak virus (UCBSV) causes the most destructive cassava disease in Tanzania. Thus, breeders urgently need CBSD-resistant cultivars to combat the impact of this disease, safeguard cassava production, improve the yields and secure food supply for communities reliant on this staple crop. In this study, we used four cassava cultivars; Albert, KBH 2002/135, KBH 2006/026 and Kiroba to explore how viral small interfering RNA (vsiRNAs), an antiviral silencing mechanism, confers CBSD resistance. Cassava plants were inoculated by grafting method using the single infection of CBSV, UCBSV and mixed infection of these viruses (co-infection). Total RNA was extracted from leaves of each cultivar followed by deep sequencing. The result showed that high level of vsiRNAs was produced in inoculated plants, with the most prominent class being 21 and 22 nucleotides. Kiroba produced the highest level of vsiRNA in both CBSV and UCBSV, whereas KBH 2006/026 produced high level of vsiRNA only with UCBSV infections. In contrast to UCBSV, inoculation with CBSV stimulated severe symptoms but relatively low levels of vsiRNA. Co-infection treatment showed a more complex interaction between the host and virus, with variations in the severity and amount of vsiRNA produced. We conclude that resistance to CBSD varies depending on the type of cultivar and virus species, and the occurrence of CBSD is suppressed in plants with elevated vsiRNA. Therefore, a good understanding on the resistance status of parental materials for breeding is recommended to breeders as a basis for improving cassava production.

中文翻译：

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木薯品种中病毒小 RNA 谱的升高可抑制木薯褐条病 (CBSD) 的发生

木薯褐条病（CBSD），由木薯褐条病毒（CBSV）引起；乌干达木薯褐条病毒（UCBSV）导致坦桑尼亚最具破坏性的木薯病害。因此，育种者迫切需要抗 CBSD 的品种来对抗这种疾病的影响，保障木薯生产，提高产量并确保依赖这种主要作物的社区的粮食供应。在这项研究中，我们使用了四种木薯品种；Albert、KBH 2002/135、KBH 2006/026 和 Kiroba 探讨了病毒小干扰 RNA (vsiRNA)（一种抗病毒沉默机制）如何赋予 CBSD 抗性。使用CBSV、UCBSV的单一感染和这些病毒的混合感染(共感染)通过嫁接方法对木薯植物进行接种。从每个品种的叶子中提取总RNA，然后进行深度测序。结果表明，接种的植物中产生了高水平的vsiRNA，其中最突出的类别是21和22核苷酸。Kiroba 在 CBSV 和 UCBSV 中产生最高水平的 vsiRNA，而 KBH 2006/026 仅在 UCBSV 感染时产生高水平的 vsiRNA。与 UCBSV 相比，接种 CBSV 会刺激严重的症状，但 vsiRNA 水平相对较低。共感染治疗显示宿主和病毒之间存在更复杂的相互作用，严重程度和产生的 vsiRNA 量存在差异。我们得出的结论是，对 CBSD 的抗性因品种类型和病毒种类而异，并且在 vsiRNA 升高的植物中，CBSD 的发生受到抑制。因此，建议育种者充分了解育种亲本的抗性状况，作为提高木薯产量的基础。