Movement of aphid-transmitted Sugarcane yellow leaf virus (ScYLV) within and between sugarcane plants

Sugarcane yellow leaf virus (ScYLV) is distributed worldwide and has been shown to be the cause of the disease sugarcane yellow leaf syndrome (YLS). This study was an investigation of the transmission and spread of ScYLV in Hawaii. Several aphids are known to transmit the virus, but investigation of infestation and transmission efficiency showed Melanaphis sacchari to be the only vector important for field spread of the disease. The initial multiplication of ScYLV in a virus-free plant occurred exclusively in very young sink tissues. When a single leaf was inoculated on a plant, that leaf and all older leaves remained virus-free, based on tissue-blot immunoassay, whereas meristems and all subsequently formed new leaves became infected. Therefore, only after those leaves which had already developed before inoculation had been shed, did the complete plant contain ScYLV. Spread of the viral infection to neighbouring plants in the plantation fields via aphids was relatively slow and in the range of a few metres per year. No indication of long-distance transfer could be seen. This indicates that it may be possible to produce and use virus-free seed cane for planting of high-yielding but YLS-susceptible cultivars.     

Variation in virus populations and growth characteristics of two sugarcane cultivars naturally infected by Sugarcane yellow leaf virus in different geographical locations

Two sugarcane cultivars (R570 and SP71-6163) naturally infected by Sugarcane yellow leaf virus (SCYLV) were each imported from several geographical locations into a sugarcane yellow leaf-free environment (Montpellier, France). Plants were grown as plant cane for 5–6 months and the experiment was repeated for three consecutive years (2003–2005) in a greenhouse. Several sugarcane-growth and disease characteristics were monitored to identify variation in pathogenicity of SCYLV. Depending on their geographical origin, sugarcane cvs R570 and SP71-6163 were infected by SCYLV genotypes BRA-PER or REU, or a mixture of the two. Severity of symptoms did not vary between plants of cv. R570, but variation in disease severity between plants of cv. SP71-6163 from different geographical locations suggested the occurrence of pathogenic variants of SCYLV. For each sugarcane cultivar, differences in stalk length, number of stalk internodes, virus titre in the top visible dewlap leaf, and percentage of infection of leaf and stalk phloem vessels were also found between plants from different geographical origins. However, these differences were not always reproducible from one year to another, suggesting occurrence of different plant responses to SCYLV isolates under varying environmental conditions.     

Elimination of Sugarcane yellow leaf virus from infected sugarcane plants by meristem tip culture visualized by tissue blot immunoassay

Sugarcane yellow leaf virus (SCYLV), a member of the Luteoviridae , is implicated in the sugarcane disease known as yellow leaf syndrome (YLS), which is characterized by yellowing of the leaf midrib followed by leaf necrosis and possible growth suppression. YLS is distributed worldwide and susceptible cultivars are commonly infected with SCYLV. However, not all cultivars infected with SCYLV show symptoms of YLS and some cultivars that show symptoms do so sporadically. Since it is difficult to obtain virus-free plants of susceptible cultivars, it has not been possible to study the factors involved in SCYLV infection nor the effects of infection on plant growth and yield. A tissue blot immunoassay was used to visualize in vivo presence of the virus so that virus-infected and virus-free plants could be distinguished. Meristem tip cultures were used to produce virus-free plantings of six SCYLV-susceptible sugarcane cultivars. Nearly all of the regenerated sugarcane lines remained virus-free over a period of up to 4 years, whether grown in isolated fields or in the glasshouse. Experimental re-infection of the virus-free plants by viruliferous aphids demonstrated that meristem tip culture did not affect susceptibility of sugarcane to SCYLV. Improved diagnosis and production of virus-free plants of SCYLV-susceptible cultivars will facilitate research to quantify the effect of the virus on yield and to analyse the processes involved in disease development.     

Sugarcane yellow leaf virus and sugarcane yellows phytoplasma: elimination by tissue culture

Yellow leaf syndrome (YLS) is a recently reported disease of sugarcane, characterized by yellowing of the leaves. Two pathogens: a virus, Sugarcane yellow leaf virus (SCYLV); and a phytoplasma, sugarcane yellows phytoplasma (SCYP), are associated with the disease. The use of tissue culture was investigated as a means to eliminate both SCYLV and SCYP from exotic varieties undergoing quarantine in Mauritius. Of 43 varieties in quarantine, 28 were infected with SCYLV and 19 with SCYP when checked by RT–PCR and nested PCR, respectively. Seventeen varieties were coinfected with both pathogens. Thirty infected varieties were induced to form callus in vitro using leaf rolls as explants. After two subcultures, 19 varieties were successfully regenerated and tested for SCYLV and SCYP. No pathogen could be detected in any regenerated plantlets. All the regenerated plants remained free from both SCYLV and SCYP over a period of 1 year in the glasshouse, confirming that the pathogens had been eliminated by tissue culture.     

Susceptibility of sugarcane, plantation weeds and grain cereals to infection by Sugarcane yellow leaf virus and selection by sugarcane breeding in Hawaii

Hawaiian commercial sugarcane cultivars (Saccharum spp.), noble canes (S. officinarum), robust canes (S. robustum) and wild relatives of sugarcane (S. spontaneum and Erianthus arundinaceus) were tested by tissue blot immunoassay to determine whether they were infected by Sugarcane yellow leaf virus (SCYLV). Two-thirds of the commercial hybrids and noble canes were infected and therefore classified as SCYLV-susceptible, in contrast to the wild cane relatives where less than one third of the varieties were infected. The pedigree list of commercial, registered cultivars showed that 80% of cultivars were SCYLV-susceptible and that also 75–90% of the progeny of resistant (female) parents were susceptible (male parents are mostly unknown because of polycross breeding). In contrast, a cross between a resistant S. robustum and a susceptible S. officinarum cultivar yielded 85% resistant progeny clones, which indicated that SCYLV-resistance is a dominant trait. It is concluded that the breeding program selected against SCYLV-resistance with the result that 80% of the newly bred cultivars were susceptible. Exceptional was the period between 1950 and 1970, in which 50% of the newly-bred clones were resistant. This is the period in which SCYLV had entered Hawaii. Weed grasses and cereal grasses which grew in or next to sugarcane fields were not infected by SCYLV. Thus SCYLV does not spread from infected sugarcane plants to adjacent grasses or cereals under field conditions, although cereal grasses can be infected experimentally.     

广东甘蔗引种基地甘蔗黄叶病毒分子鉴定

 甘蔗黄叶病1989年首先发现于美国夏威夷,当时不知其病原性质,称为甘蔗黄叶综合症。1990年以来,该病在世界多个蔗区发生,引起严重的产量损失^[1,2]。     

广东甘蔗黄叶病田间调查及病原病毒的分子检测

 广东省粤北和粤西蔗区多个县市的田间甘蔗上观察到甘蔗黄叶病(Sugarcane yellow leaf disease,SYLD)典型症状,目前该病仅局部分布,但部分田块病株率为5%~80%,发病品种有青皮果蔗、黑皮果蔗、新台糖系列品种、粤糖79/177和粤糖93/159等。采集发病田间显症叶片、无症叶片和在病叶上取食的甘蔗绵蚜(Ceratovacuna lanigera)样品,抽提总RNA,以基于甘蔗黄叶病毒(Sugarcane yellow leaf virus,SCYLV) CP基因序列的特异引物进行一步RT-PCR和巢式PCR扩增,并对扩增产物进行核苷酸序列测定和BLAST比对。结果显示,RT-PCR及巢式PCR产物核苷酸序列与分离自巴西的SCYLV B1株系相应区段同一率为100%;一步RT-PCR可从约70%的显症叶片样品中检测到SCYLV,而病田中的无症叶片样品以及在病叶上取食的单头甘蔗绵蚜样品需经巢式PCR扩增方可检测到SCYLV,阳性率分别为1%~5%和83%。本研究表明,广东省栽培甘蔗已受到SCYLV侵染,甘蔗绵蚜携带SCYLV。     

甘蔗黄叶病毒运动蛋白的原核表达和抗血清制备

甘蔗黄叶病毒(Sugarcane yellow leaf virus,ScYLV)属于黄症病毒科(Luteoviridae)、马铃薯卷叶病毒属(Polerovirus),主要由蚜虫传播,能够侵染甘蔗、玉米等多种作物,引发严重的植物病害。本研究将编码ScYLV运动蛋白(Movement protein,MP)的基因连接到pDB-His-MBP原核表达载体上,转化到大肠杆菌菌株Rosetta中,经IPTG诱导,表达分子量大小约为70 kDa的融合蛋白,将纯化后的融合蛋白制备多克隆抗血清。利用western blot检测抗血清的效价为1∶128 000,灵敏度为1∶256,抗血清不与马铃薯卷叶病毒属(Polerovirus)的其它病毒以及黄症病毒属(Luteovirus)病毒发生交叉反应,具有很好的特异性。本文制备的ScYLV MP抗血清可以用于ScYLV的检测,并为深入研究ScYLV与寄主的相互作用等问题提供材料基础。     

A new approach to evaluate relative resistance and tolerance of tomato cultivars to begomoviruses causing the tomato yellow leaf curl disease in Spain

A simple procedure to evaluate relative resistance and tolerance of tomato cultivars to the begomoviruses causing tomato yellow leaf curl (TYLC) disease in Spain was developed. To estimate the resistance and tolerance levels of a cultivar, several formulae were developed based on the ratio of infected plants, virus titre (estimated by tissue–print hybridization) and symptom intensity. The formulae were applied to five commercial tomato cultivars (Amoretto, Birloque, Royesta, Tovigreen and Ulises) naturally infected by TYLC viruses. The analyses showed that Ulises, Birloque and Tovigreen exhibited a moderate resistance, and Ulises was also highly tolerant. There was a positive correlation between symptom intensity and virus titre in infected plants, suggesting that the hybridization technique could also be used as an early estimator of tolerance. Finally, molecular hybridization and nucleotide sequence analyses of the begomovirus intergenic region showed that the local TYLC virus population consisted of a single species, Tomato yellow leaf curl virus (TYLCV, formerly TYLCV-Israel), with low genetic variation (nucleotide identity between isolates higher than 97%).     

甘蔗黄叶病及其病原分子生物学研究进展

甘蔗黄叶病是由甘蔗黄叶病毒(Sugarcane yellow leaf virus,SCYLV)引起的一种病毒病害,在全球主要甘蔗种植国家或地区普遍发生,危害日益严重。SCYLV经甘蔗蚜虫以持久性方式传播,在寄主植株内主要侵染韧皮部组织。该病毒起源于黄症病毒科属间基因重组,被国际病毒分类命名委员会确认为黄症病毒科马铃薯卷叶病毒属成员。文章综述了甘蔗黄叶病毒生物学特征、病害发生和危害、病原鉴定和检测、分子进化和遗传多样性、基因组结构和基因功能以及抗病转基因等方面研究进展,并对甘蔗黄叶病抗病育种和防治措施作了讨论。     

Impact of Sugarcane yellow leaf virus on Sugarcane Yield and Juice Quality in Réunion Island

Sugarcane yellow leaf virus (SCYLV) was first detected in sugarcane of Réunion Island in 1997. A field experiment was undertaken to assess the potential impact of this virus on sugarcane production. The agronomic characteristics of SCYLV-infected plants were compared to those of virus-free plants of three sugarcane cultivars (R570, R577 and R579) which occupy more than 90% of the cultivated sugarcane area on Réunion Island. In the plant crop, significant losses in stalk weight (28%) and in sugar content (11%) were detected for cultivar R577, but not for either of the two other cultivars. In the first ratoon crop, yield reduction was detected for cultivar R577 (37%), but also for cultivar R579 (19%). Cultivar R577 also showed significant losses in sugar content (12%) due to reduced amount and quality of extracted cane juice. No yield reduction was found for cultivar R570, although stalk height and diameter were reduced in SCYLV-infected canes of this cultivar in the first ratoon crop. Leaf yellowing was observed at harvest of plant and ratoon crops when sugarcane was no longer irrigated, and 10–59% of symptomatic stalks could be attributed to the presence of SCYLV. The most severe yellowing symptoms were related to infection of sugarcane by the virus.     

Impact of <Emphasis Type="Italic">Sugarcane yellow leaf virus</Emphasis> on growth and sugar yield of sugarcane

A survey revealed that Sugarcane yellow leaf virus (SCYLV) is found on all Hawaiian sugarcane plantations including those where no yellow leaf symptoms were observed. In a comparison of growth and yield between SCYLV-infected and SCYLV-free plants of the cultivar H87-4094, germination and early shoot growth of infected plants were retarded. The number of stalks per stool was reduced by 30%, biomass was reduced by 29%, and sugar yield by 26% when plants were harvested after 11 months. Yields did not decrease when plants were harvested after 2 years. Thus, SCYLV could reduce yield, even when the plants were asymptomatic. In a field test of SCYLV-susceptible (infected) and -resistant cultivars to compare growth and yield, 10 commercial cultivars (six susceptible and four resistant to SCYLV) were grown in eight fields with different climates and soils. Primary stalk length, biomass and sugar yield did not differ between susceptible and resistant cultivars under any field conditions. Thus, harmful effects of SCYLV on yield cannot be deduced by comparing different cultivars.     

黄淮地区小麦品种对小麦黄花叶病毒抗性评价

小麦黄花叶病是由禾谷多黏菌传播的小麦黄花叶病毒引起的病害,近年在黄淮麦区呈蔓延加重趋势。为了给病害的防治和抗病育种工作提供依据,本研究利用分级评价方法对黄淮地区推广的小麦品种进行了田间抗病性鉴定。两年鉴定结果表明,在145个供试小麦品种中,‘濮优938’、‘新麦208’、‘豫麦416’、‘新原958’、‘豫麦70-36’、‘泛麦5号’等70个品种表现为免疫,占总数的48.28%;‘豫麦47’和‘邯6172’表现为抗病,占总数的1.38%;‘洪育2号’、‘花培2号’、‘偃展4110’、‘豫麦41’、‘郑麦9023’等48个品种表现为中抗,占总数的33.10%;‘兰天06129’、‘兰天0591’、‘徐麦9158’、‘徐麦0054’、‘徐麦1108’等25个品种表现为感病,占总数的17.24%。研究结果为指导小麦黄花叶病区合理选择小麦品种提供了科学依据。     

果蔗脱毒种苗甘蔗花叶病、黄叶病和宿根矮化病分子检测

为监测2016-2017年种植的果蔗脱毒种苗脱毒效果,分别采集广州市南沙区和增城区、湛江市麻章区及华南农业大学甘蔗育种基地共83份果蔗脱毒种苗样本,进行甘蔗花叶病毒(SCMV)、高粱花叶病毒(SrMV)和甘蔗黄叶病毒(SCYLV)RT-PCR检测。结果表明SCMV的阳性样本数为3个,阳性检出率3.61%;SrMV的阳性样本数为0;SCYLV的阳性样本数为78个,阳性检出率93.98%。采用常规PCR和巢式PCR技术对采集于广州市增城区和华南农业大学甘蔗育种基地的30份果蔗脱毒种苗样本进行宿根矮化病菌(Lxx)检测,常规PCR检测阳性样本数为0,巢式PCR检测疑似阳性样本数为8,疑似阳性检出率26.67%。本研究采用茎尖组织培养脱毒技术培育的果蔗脱毒种苗能有效脱除果蔗种苗内的SCMV、SrMV和Lxx,但SCYLV的脱除效果有待进一步研究。     

甘蔗黄叶病毒外壳蛋白基因克隆及其实时荧光RT-PCR检测

 甘蔗黄叶病毒（Sugarcane yellow leaf virus, SCYLV）引起的甘蔗黄叶病是一种新的全球性病毒病害。本文以YLSCPF1和YLSCPR591为引物,采用RT-PCR方法克隆了甘蔗黄叶病毒福建分离物（CHN-FJ1）外壳蛋白（CP）基因,编码196个氨基酸。分析不同地理来源的SCYLV病毒分离物cp基因核苷酸及其推导编码的氨基酸序列,同源性达95%以上。根据cp基因的保守序列,设计1对特异性引物和TaqMan探针,建立了SCYLV的TaqMan实时荧光RT-PCR方法。结果表明,检测下限为初始质粒模板DNA 1 000拷贝/μL（约3.61 fg/μL）,比常规PCR方法的灵敏度提高100倍。检测甘蔗花叶病毒、宿根矮化病菌和黑穗病菌,没有典型的扩增曲线和无Ct值。应用实时荧光RT-PCR、常规RT-PCR和组织印迹免疫杂交（TBIA）对田间甘蔗叶片样品进行检测,阳性检出率分别为100%、61.5%和69.2%,表明该方法比常规RT-PCR和TBIA具有更高的灵敏度,适合于对SCYLV的检测。     

我国甘蔗主要杂交亲本黄叶病病原鉴定及田间发病率

甘蔗黄叶病是一种发生普遍、危害严重的病毒病害,选育抗病品种是控制该病发生与蔓延的有效措施.利用逆转录-聚合酶链反应(RT-PCR)、组织印迹杂交免疫测定(TBIA)和抗原直接包被酶联免疫吸附(DAC-ELISA)方法对我国43份甘蔗主要杂交亲本黄叶病病原(Sugarcane yellow leaf virus,SCYLV)进行鉴定,并调查SCYLV田间自然侵染条件下甘蔗黄叶病发病率.已明确36份亲本材料感染或未感染SCYLV,其中32份鉴定结果为阳性,品种(系)感病率达88.9％.甘蔗植株田间自然发病率可分为无发病、发病率低、中等和高4个等级,方差分析表明,各等级间的植株发病率差异达极显著水平(P＜0.01).从美国引进的多数CP和HoCP系列亲本发病率较高,而多数崖城和新台糖系列亲本材料的发病率较低,可作为甘蔗抗黄叶病杂交亲本.     

Developing Groundnut Lines with Resistance to Seed Colonisation by Toxin-producing Strains of Aspergillus Species

Abstract

Evidence for the possible development of groundnut (Arachis hypogaea L.) cultivars with favourable agronomic characteristics and resistance to aflatoxinproducing strains of Aspergillus species is presented. In studies of F₂ and F₃ progenies from crosses of resistant and susceptible genotypes data on the frequency distribution and least square estimates of genetic effects showed the possibility of selecting for resistance to seed colonisation by the fungus. Yield, value and seed quality data for seven advanced lines developed by using pedigree selection from crosses showed that potential favourable groundnut cultivars may be developed.