Cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) are two viral diseases that cause severe yield losses in cassava of up to 100%, thereby persistently threatening food and income security in sub-Saharan Africa. For effective management of these diseases, there is a critical need to develop and deploy varieties with dual resistance to CBSD and CMD. In this study, we determined the response of advanced breeding lines to field infection by cassava brown streak viruses (CBSVs) and cassava mosaic begomoviruses (CMBs). This aim helped in identifying superior clones for downstream breeding. In total, 220 cassava clones, three in uniform yield trials (UYTs) and 217 in a crossing block trial (CBT), were evaluated for virus and disease resistance. Field data were collected on disease incidence and severity. To detect and quantify CBSVs, 448 and 128 leaf samples from CBSD symptomatic and symptomless plants were analyzed by reverse transcription PCR and real-time quantitative PCR, respectively. In addition, 93 leaf samples from CMD symptomatic plants in the CBT were analyzed by conventional PCR using CMB species-specific primers. In the CBT, 124 (57%) cassava clones did not express CMD symptoms. Of the affected plants, 44 (55%) had single African cassava mosaic virus infection. Single Cassava brown streak virus (CBSV) infections were more prevalent (81.6%) in CBT clones than single Ugandan cassava brown streak virus (UCBSV) infection (3.2%). Of the three advanced clones in the UYT, NAROCASS 1 and NAROCASS 2 had significantly lower (P < 0.05) CBSD severity, incidence, and CBSV load than MH04/0300. In the UYT, only 22% of samples tested had CBSVs, and all showed a negative result for CMBs. The low disease incidence, severity, and viral load associated with NAROCASS 1 and NAROCASS 2 is evidence of their tolerance to both CBSD and CMD. Therefore, these two cassava clones should be utilized in CBSD and CMD management in Uganda, including their utilization as progenitors in further virus resistance breeding.

中文翻译：

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乌干达先进木薯育种克隆对主要病毒感染的抵抗力

木薯褐条病 (CBSD) 和木薯花叶病 (CMD) 是两种病毒性疾病，可导致木薯严重减产高达 100%，从而持续威胁撒哈拉以南非洲的粮食和收入安全。为了有效管理这些疾病，迫切需要开发和部署对 CBSD 和 CMD 具有双重抗性的品种。在这项研究中，我们确定了先进育种品系对木薯褐条病毒（CBSV）和木薯花叶病毒（CMB）田间感染的反应。这一目标有助于确定下游育种的优质克隆。总共评估了 220 个木薯克隆的病毒和抗病性，其中 3 个在统一产量试验 (UYT) 中，217 个在交叉块试验 (CBT) 中。收集有关疾病发生率和严重程度的现场数据。为了检测和量化 CBSV，分别通过逆转录 PCR 和实时定量 PCR 分析了来自 CBSD 有症状和无症状植物的 448 个和 128 个叶子样本。此外，使用 CMB 物种特异性引物通过常规 PCR 分析了 CBT 中来自 CMD 症状植物的 93 个叶子样本。在 CBT 中，124 个（57%）木薯克隆没有表现出 CMD 症状。在受影响的植物中，44 株（55%）感染了单一非洲木薯花叶病毒。在 CBT 克隆中，单一木薯褐条病毒 (CBSV) 感染 (81.6%) 比单一乌干达木薯褐条病毒 (UCBSV) 感染 (3.2%) 更为普遍。在 UYT 中的三个高级克隆中，NAROCASS 1 和 NAROCASS 2 的 CBSD 严重程度、发生率和 CBSV 负荷显着低于 MH04/0300（P < 0.05）。在 UYT 中，只有 22% 的测试样本有 CBSV，并且所有样本的 CMB 均为阴性。与 NAROCASS 1 和 NAROCASS 2 相关的低疾病发病率、严重程度和病毒载量证明了它们对 CBSD 和 CMD 的耐受性。因此，这两个木薯克隆应用于乌干达的 CBSD 和 CMD 管理，包括将它们用作进一步的病毒抗性育种中的祖细胞。