Chaparro-Martínez E I, Trujillo-Pinto G
Facultad de Agronomía, Universidad Central de Venezuela, Ar. 2101, Apdo. 4579, Maracay, Venezuela.
Plant Dis. 2001 Dec;85(12):1285. doi: 10.1094/PDIS.2001.85.12.1285D.
Frogskin disease (FSD) is a disease of clonally propagated cassava (Manihot esculenta Crantz) and has been reported to reduce cassava yields significantly in South America (1). FSD is caused by an uncharacterized virus that is restricted to South America. The evidence indicates FSD is transmitted by stem cuttings and graft (3). However, little information is available on its distribution and incidence in Venezuela. Eighty-seven samples with virus-like symptoms were collected with the help of technical staff and producers in cassava-producing states: Amazonas (1 sample), Aragua (7 samples), Barinas (35 samples), Cojedes (8 samples), Monagas (19 samples), and Portuguesa (17 samples). In these states, the average daytime temperature was 26°C, but the average was higher (>28°C) during the dry season. Samples were collected during the rainy season because high temperatures and dry field conditions appeared to suppress symptom expression, while cooler conditions tended to favor symptom development (2). Roots of sampled cassava plants were examined for the presence of FSD. A single 70- to 80-cm-long stem cutting was taken from each plant and subdivided into four pieces. Two pieces were used as rootstocks in graft-inoculation tests with Secundina scions for FSD detection, and two pieces were potted in sterilized soil to be used in other tests. All potted and grafted plants were kept in the Vegetable Virology Laboratory of the Faculty of Agronomy (Universidad Central de Venezuela), at an average temperature of 24°C and 80% relative humidity. FSD-infected plants were identified by mosaic symptoms on Secundina scions and the presence of 80-nm spherical viral particles. Most FSD-infected cultivars expressed only root symptoms. However, in the case of Secundina cvs. MCOL 22 and MCOL 113, foliar symptoms were also detected (1). FSD was found in a simple infection in one cassava sample from Aragua State (14.3% incidence, 1 of 7 samples) and in four cassava samples from Barinas State (11.4% incidence, 4 of 35 samples) associated with Cassava virus X (detected by double-antibody sandwich enzyme-linked immunosorbent assay). To our knowledge, this is the first report of FSD detection in Venezuela. References: (1) E. A. Frison et al. Informe Anual. CIAT, Cali, Colombia, 1995. (2) B. L. Nolt et al. Plant Pathol. 41:384, 1992. (3) Technical Guidelines for the Safe Movement of Cassava Rome. FAO/IBPGR. p. 10-27, 1991.
木薯蛙皮病（FSD）是一种发生于无性繁殖木薯（Manihot esculenta Crantz）的病害，据报道在南美洲会显著降低木薯产量（1）。FSD由一种仅在南美洲发现的未鉴定病毒引起。有证据表明FSD通过茎切段和嫁接传播（3）。然而，关于其在委内瑞拉的分布和发病率的信息却很少。在木薯种植州，借助技术人员和种植者收集了87份有病毒样症状的样本：亚马逊州（1份样本）、阿拉瓜州（7份样本）、巴里纳斯州（35份样本）、科赫德斯州（8份样本）、莫纳加斯州（19份样本）和葡萄牙萨州（17份样本）。在这些州，白天平均温度为26°C，但旱季平均温度更高（>28°C）。样本在雨季收集，因为高温和干旱的田间条件似乎会抑制症状表现，而较凉爽的条件往往有利于症状发展（2）。检查采样木薯植株的根部是否存在FSD。从每株植物上取一段70至80厘米长的单一茎切段，并分成四段。两段用作砧木，与Secundina接穗进行嫁接接种试验以检测FSD，两段种植在无菌土壤中用于其他试验。所有盆栽和嫁接植物都保存在委内瑞拉中央大学农学院蔬菜病毒学实验室，平均温度为24°C，相对湿度为80%。通过Secundina接穗上的花叶症状和80纳米球形病毒粒子的存在来鉴定感染FSD的植物。大多数感染FSD的品种仅表现根部症状。然而，对于Secundina品种MCOL 22和MCOL 113，也检测到了叶片症状（1）。在阿拉瓜州的一个木薯样本中发现了单纯感染的FSD（发病率14.3%，7份样本中的1份），在巴里纳斯州的四个木薯样本中也发现了FSD（发病率11.4%，35份样本中的4份），这些样本与木薯X病毒相关（通过双抗体夹心酶联免疫吸附测定法检测）。据我们所知，这是委内瑞拉首次关于检测到FSD的报告。参考文献：（1）E. A. Frison等人。年度报告。国际热带农业中心，哥伦比亚卡利，1995年。（2）B. L. Nolt等人。植物病理学。41:384，1992年。（3）木薯安全运输技术指南。罗马。粮农组织/国际植物遗传资源委员会。第10 - 27页，1991年。
