Cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) are two important biotic constraints affecting cassava (Manihot esculenta Crantz) production in sub-Saharan Africa, and the deployment of cassava varieties dually resistant to both diseases is the most effective and realistic way of reducing losses. Crosses were carried out between a Tanzanian local cassava cultivar (Namikonga) and a South American cassava genotype (AR37-80) to develop dual-resistant progenies, and they were evaluated for two seasons at Naliendele in Southern Tanzania, which is a CMD and CBSD hot spot area. The CMD-resistant progenies had low foliar severities (≤1.8), similar to the CMD-resistant parent. The CBSD-resistant progenies had minimal foliar (≤2.0) and root necrosis (≤1.2) severities, similar to the CBSD resistant parent, whereas CBSD-tolerant progenies had severe foliar severities up to 3.3 but minimal root necrosis severities (≤1.2). Traits with minimal environmental influence also had high heritability (≥0.65) and high selection accuracy (≥0.70), and they included CMD foliar symptoms, CBSD foliar symptoms at 6 mo after planting, root necrosis, root necrosis incidence, root weight, root number per plant, and harvest index. Correlation analysis showed that the presence of disease reduces usable roots, root weight, root number per plant, and harvest index. Dual resistance can improve yield as observed in Namar 050 and Namar 371, which had high root weights of 27.5 and 28.2 t ha⁻¹ with high genetic gains of 56.1 and 58.5%, respectively. Dual-resistant progenies identified were Namar 050, Namar 100, Namar 130, Namar 200, Namar 334, Namar 371, and Namar 479, as they had minimal CMD and CBSD symptom severities (≤2.0) and could be used for breeding cassava varieties with superior characteristics.

中文翻译：

---

开发针对两种主要病毒性疾病的双重抗性木薯

木薯花叶病 (CMD) 和木薯褐条病 (CBSD) 是影响木薯 ( Manihot esculentaCrantz) 在撒哈拉以南非洲生产，部署对这两种疾病具有双重抗性的木薯品种是减少损失的最有效和现实的方法。坦桑尼亚当地木薯品种（Namikonga）与南美木薯基因型（AR37-80）杂交培育双抗后代，并在坦桑尼亚南部的Naliendele进行了两个季节的评估，这是一个CMD和CBSD热点地区。CMD 抗性后代的叶严重程度较低（≤1.8），与 CMD 抗性亲本相似。CBSD 抗性后代具有最小的叶 (≤2.0) 和根坏死 (≤1.2) 严重程度，类似于 CBSD 抗性亲本，而 CBSD 耐受后代的叶严重程度高达 3.3，但根坏死严重程度最低 (≤1.2)。环境影响最小的性状也具有高遗传力（≥0.65）和高选择精度（≥0.70），它们包括CMD叶面症状、种植后6个月的CBSD叶面症状、根坏死、根坏死发生率、根重、根数每株植物和收获指数。相关性分析表明，疾病的存在会降低可用根、根重、每株植物的根数和收获指数。在 Namar 050 和 Namar 371 中观察到的双重抗性可以提高产量，它们的根重高达 27.5 和 28.2 吨公顷 相关性分析表明，疾病的存在会降低可用根、根重、每株植物的根数和收获指数。在 Namar 050 和 Namar 371 中观察到的双重抗性可以提高产量，它们的根重高达 27.5 和 28.2 吨公顷 相关性分析表明，疾病的存在会降低可用根、根重、每株植物的根数和收获指数。在 Namar 050 和 Namar 371 中观察到的双重抗性可以提高产量，它们的根重高达 27.5 和 28.2 吨公顷^{-1 分别}具有 56.1% 和 58.5% 的高遗传增益。鉴定的双重抗性后代为 Namar 050、Namar 100、Namar 130、Namar 200、Namar 334、Namar 371 和 Namar 479，因为它们的 CMD 和 CBSD 症状严重程度最低（≤2.0），可用于育种优越的特性。