Cassava common mosaic virus infection affects growth and yield components of cassava plants (Manihot esculenta) in Argentina

Cassava is an important crop with great economic and social significance in many countries. Most of its biomass is usable: storage roots can be destined for industry or fresh consumption, leaves are a source of protein, vitamins, and minerals, and stems can be used as propagation material. Due to its vegetative propagation, cassava yield is greatly constrained by viral diseases. Cassava common mosaic virus (CsCMV), one of the most widely spread viruses in Latin America, is the only cassava-infecting potexvirus able to cause disease in a single infection: cassava common mosaic disease (CCMD). Here, we evaluated the effect of an Argentinian strain of CsCMV on several agronomic traits. Field trials were established in north-eastern Argentina for three successive cropping seasons, 2016/17, 2017/18, and 2018/19. CsCMV presence was confirmed by PCR or ELISA tests in mechanically inoculated cassava plants. The evaluated traits were plant height (PH), total fresh weight (TFW), shoot fresh weight (SFW), diameter and FW of tuberous root per plant (TRD and FWTR), FW of each individual tuberous root (FWiTR), length and number of tuberous roots (TRL and TRN), harvest index (HI), and estimated yield of tuberous root (EY) in both infected and noninfected plants. Significant yield losses were recorded in infected plants. The most affected traits were EY and FWTR (both showing 44.3% of losses), followed by TFW, SFW, TRN, and FWiTR (37.8%, 33.5%, 29.9%, and 24.8% of losses, respectively). These losses are extremely high for Argentina, where this crop provides food security and demand for the raw material is unsatisfied.     

Surveys of cassava plantations in Colombia for virus and virus-like diseases

The cassava common mosaic virus (CsCMV) and the frogskin (FSD) disease agent have been reported to reduce cassava yields significantly in South America. However, little information is available on the distribution and incidence of these and other cassava virus diseases in Colombia. Cassava plants collected in three principal cassava production zones of Colombia were tested for the presence of CsCMV, cassava × virus (CsXV), and the Caribbean mosaic disease (CMD) and FSD agents. Some plants were also tested for the presence of double-stranded RNA (dsRNA). CsCMV was not detected in any of the 870 plants from 86 plantations. CsXV was detected in 51% of the 150 plants collected in the Cauca Department in south-central Colombia. The virus was present on all 15 cassava plantations surveyed. The CMD agent was detected in 17% of the 138 plants sampled in the Department of Magdalena in northern Colombia. FSD root symptoms were observed on 25 and 3% of plants examined in the Departments of Cauca and Magdalena, respectively. None of the 570 plants collected in areas west of the Rio Magdalena in the Departments of Atläntico, Bolivar, Córdoba and Sucre were found to be infected with any of these disease agents. However, some plants sampled in this region were found to contain multiple dsRNA species of unknown origin.     

Distinct strains of the re‐emergent Cassava common mosaic virus (genus: Potexvirus) infecting cassava in Argentina

Cassava common mosaic disease (CCMD) has been reported in all regions where cassava is grown in the Americas and the causal agent, Cassava common mosaic virus (CsCMV), has been identified as a mechanically transmitted potexvirus (Alphaflexiviridae). In Argentina, cassava is grown mainly in the northeast (NEA) region that shares borders with Brazil and Paraguay. Increasing incidences of CCMD were observed during the years 2014 to 2016 associated with severe leaf mosaic symptoms and yield reductions where the occurrence of CsCMV was confirmed by RT‐PCR and sequencing. In this work, the virus has been successfully purified and a double‐antibody sandwich (DAS‐) ELISA test has been developed from an Argentinean isolate of CsCMV to extend the diagnostics of the disease. A collection of 726 samples was screened and CsCMV was detected with 100% prevalence in the NEA region. Additional co‐infecting viruses were detected in some plants (64.4%); in these, CCMD symptoms correlated with CsCMV only, although more severe symptoms could be observed in mixed infected plants. Sequence analysis of the conserved RdRp domain showed a wider diversity of CsCMV isolates. Interestingly, a separate phylogenetic cluster was formed by isolates from the NEA region that only shared 77.1% to 80.3% nucleotide identity with the other clusters. These results indicate the presence of mixed strains occurring in the NEA region and suggest the presence of geographically distinct strains of CsCMV in South America.     

甘肃省大丽花病毒病病原鉴定及病生理研究

经对受病毒感染的甘肃省临洮县大丽花进行间接ELISA和鉴别寄主测定,结果表明黄瓜花叶病毒(CMV)是其病原之一。田间调查表明大丽花病毒病在甘肃临洮县发生普遍,发病率达36%;其主要症状有花叶、卷叶花叶、蕨叶和矮缩。不同大丽花品种之间病毒病发病率有一定的差异,在调查的8个品种中‘鹦嘴红’发病率最低,只有7.43%,而‘洮阳荷花’发病率最高,达到42.47%。大丽花感染病毒后叶绿素(a+b)比正常的下降了23.61%;在叶片组织病变观察中,发现叶片感染病毒后叶绿体内的淀粉颗粒含量增多且肿大,油粒增多,几乎占满整个叶绿体结构。     

马铃薯Y病毒侵染对叶绿体超微结构、光合和荧光参数的影响

 马铃薯Y病毒(PVY)侵染导致马铃薯叶片叶绿体个体变小,部分叶绿体的结构遭到破坏,淀粉粒的体积变小而粒数密度提高。随着病毒侵染,叶片中的叶绿素含量逐步减少,光合系统电子传递速率和净光合速率显著下降,而光系统Ⅱ的最大光化学效率则没有显著变化。PVY导致叶绿体结构破坏和碳同化酶活性下降,可能是造成光合作用下降的主要原因。     

Effect of pokeweed antiviral protein (PAP) on the infection of plant viruses

At a concentration of 0.4 μg purified pokeweed antiviral protein (PAP)/ml, the formation of local lesions on tobacco leaves caused by tobacco mosaic virus infection was completely inhibited and at 25 ng PAP/ ml. 68% inhibition was still obtained. PAP protected plants from infection by viruses from seven virus groups-five RNA viruses: tobacco mosaic virus, cucumber mosaic virus, alfalfa mosaic virus, potato virus X and potato virus Y; and two DNA viruses: African cassava mosaic virus (ssDNA) and cauliflower mosaic virus (dsDNA). Virus infection was probably blocked by PAP at a very early stage. PAP infiltrated into the intercellular spaces through the lower surfaces of leaves inhibited infection by virus inoculated on the upper leaf surface, and partially prevented PVY transmission by aphids. However. PAP did not show any activity against two bacterial and six fungal pathogens.     

百合无症病毒对百合光合生理、酶活性及叶绿体超微结构的影响

 以东方百合“西伯利亚”为试验材料,研究百合无症病毒(LSV)侵染百合对其叶片生理生化以及叶绿体超微结构的影响。检测结果表明:叶片中叶绿素a、b以及总叶绿素含量与健康对照相比分别下降了28.6%、33.3%和23.5%,净光合速率、气孔导度及胞间CO₂浓度分别下降33.3%、25%和13.8%;超氧化物歧化酶(SOD)、过氧化物酶(POD)、多酚氧化酶(PPO)和苯丙氨酸解氨酶(PAL)与健康对照相比,分别增加了16.6%、29.4%、16.7%和22.2%。电镜观察发现:感病植株叶绿体膨胀变形,基质片层散乱,叶绿体内淀粉粒肿大且数目增多,从而证明LSV侵染破坏叶绿体结构,影响植株的光合作用。     

Economic impact of Turnip mosaic virus, Cauliflower mosaic virus and Beet mosaic virus in three Kenyan vegetables

Screenhouse experiments conducted in Kenya showed that inoculation of cabbage seedlings with Turnip mosaic virus (TuMV), either alone, or in combination with Cauliflower mosaic virus (CaMV), reduced the number and weight of marketable harvested heads. When viruses were inoculated simultaneously, 25% of cabbage heads were non-marketable, representing 20-fold loss compared with control. By contrast, inoculation with CaMV alone had insignificant effects on cabbage yield. This suggests that TuMV is the more detrimental of these pathogens, and its management should be a priority. Early exposure to TuMV produced cabbages that were 50% lighter than non-infected plants, but later infection was less damaging suggesting that controlling virus infection at the seedling stage is more important. TuMV was far less damaging to kale than it was to cabbage; although high proportions of TuMV-inoculated kale plants showed symptoms (>90%), the marketability and quality of leaves were not significantly reduced, and no clear relationship existed between timing of infection and subsequent crop losses. Early inoculation of Swiss chard with Beet mosaic virus (BtMV) significantly impaired leaf quality (∼50% reduction in marketable leaf production), but the impact of disease was greatest in plants that had been inoculated at maturity, where average leaf losses were two and a half times those recorded in virus-free plants. Disease-management of BtMV in Swiss chard is important, therefore, not only at the seedling stage, but particularly when plants are transplanted from nursery to field.     

Physiological response of yellow vein mosaic virus-infected bhendi [Abelmoschus esculentus] leaves

The effect of okra yellow vein mosaic virus infection on PS II efficiency and thylakoid membrane protein changes in field-grown bhendi (Abelmoschus esculentus) leaves was studied. The degree of virus infection was determined by means of the ratio of variable to maximum chlorophyll fluorescence (F_v/F_m). Changes in photosynthetic pigments, soluble proteins, nitrate reductase, photosynthetic activities and thylakoid membrane proteins were investigated. Okra yellow vein mosaic virus infection resulted in the reduction of photosynthetic pigments, soluble proteins, ribulose-1, 5-bisphosphate carboxylase activity and nitrate reductase activity. Virus infection caused marked inhibition of PS II activity. The artificial electron donors, diphenyl carbazide and hydroxylamine significantly restored the loss of PS II activity in infected leaves. The marked loss of PS II activity in infected leaves may be due to the loss of 47, 33, 28–25, 17 and 15 kDa polypeptides. It is concluded that the yellow vein mosaic virus infection inactivates the donor side of PS II.     

Effect of fluazifop-butyl on the chlorophyll content, fluorescence and chloroplast ultrastructure of Elymus repens (L.) Gould. leaves

Some aspects of the action of fluazifop-butyl on the chlorophyll content, chloroplast functioning and chloroplast ultrastructure of Elymus repens are reported. Over a period of 0–12 days after spraying with 0.25 or 1.0 kg ha^?1 of the herbicide, chlorophyll a and b contents of this susceptible plant decreased, progressing from the youngest to the more mature leaves. Newly formed tillers and the youngest expanding leaves exhibited a more severe type of chlorosis and were often found to be devoid of chlorophyll. A similar progressive decline of the chlorophyll content was observed in an experiment where leaf segments were floated in fluazifop-butyl. Evidence of a rapid and significant alteration of the normal chlorophyll fluorescence of E. repens leaves treated with fluazifopbutyl was obtained. The herbicide, at a concentration range of 0.25–1.0 μg μ1^?1, caused a significant loss of the fast fluorescence rise, fluorescence yield and, after 24 h, caused a total abolition of the fluorescence decay (PS decas). These results are discussed. Ultrastructural damage to chloroplasts was seen within 24 h after treatment with fluazifop-butyl. This damage ranged from a partial to total disruption of the outer chloroplast envelope and a disorganization of the internal thylakoid system. Such Ultrastructural effects on chloroplasts were found to intensify up to about 6–7 days after spraying, by which time nearly all chloroplasts in tissue sections were affected to some degree.     

BSMV infection inhibits chlorophyll biosynthesis in barley plants

Protochlorophyllide forms, their phototransformation in the greening process and the ultrastructure of the etioplasts were studied in BSMV-infected barley plants. The aim of this work was to determine whether the chlorotic symptoms caused by the infection of this virus result from inhibition of chlorophyll biosynthesis. 77 K fluorescence emission spectra of dark-grown, flash-illuminated and re-darkened leaves and transmission electron micrographs suggested that the BSMV infection did not cause specific changes in chlorophyll biosynthesis or in chloroplast development. However, infection accelerated senescence and inhibited or delayed chlorophyll biosynthesis similar to general stress effects.     

Identification of a defective molecule derived from DNA-A of the bipartite begomovirus of East African cassava mosaic virus

Geminivirus defective interfering DNAs arise spontaneously in mechanically inoculated test plants, and have previously been found with DNA-B of the bipartite cassava mosaic geminiviruses, but not DNA-A. Reported here for the first time is the cloning and characterization of a naturally occurring truncated form of cassava mosaic geminivirus DNA-A, which at 1525 nt is around half the expected full size. Sequence analysis has shown it to be a defective (df) form of East African cassava mosaic virus (EACMV) DNA-A that has retained its cis elements essential for replication by the helper virus, and it has been termed df DNA-A 15. Phylogenetic comparisons placed the df DNA-A 15 molecule close to mild and severe isolates of EACMV-UG2. Biolistic inoculation of Nicotiana benthamiana with infectious df DNA-A 15 clone and East African cassava mosaic Cameroon virus (EACMCV) resulted in symptom amelioration as compared with EACMCV singly inoculated plants, and there was an accumulation of df DNA-A 15 in systemically infected leaves. In addition, the level of EACMV DNA-B accumulation was reduced in the coinoculated plants compared with those inoculated with EACMCV alone. PCR and sequence analysis confirmed the helper virus as EACMV.     

Molecular epidemiology of cassava mosaic disease in Madagascar

Cassava is the staple food for hundreds of millions of people in Africa but its cultivation is seriously constrained by cassava mosaic disease (CMD) in Madagascar, and in Africa in general. This study identified the cassava mosaic geminiviruses (CMGs) involved in CMD in Madagascar and their associated epidemiological characteristics from countrywide surveys. Molecular characterization of CMGs in Madagascar revealed an unprecedented diversity and co‐occurrence of six viruses: African cassava mosaic virus (ACMV), East African cassava mosaic Cameroon virus (EACMCV), East African cassava mosaic Kenya virus (EACMKV), East African cassava mosaic virus (EACMV), South African cassava mosaic virus (SACMV) and the recently described Cassava mosaic Madagascar virus (CMMGV). Distinct geographical distributions were observed for the six viruses. While ACMV was more prevalent in the central highlands, EACMV and EACMKV were prevalent in lowlands and coastal regions. Both EACMCV and SACMV occurred in almost all the localities visited. PCR diagnosis revealed that mixed infection (up to four co‐infected viruses) occurred in 21% of the samples and were associated with higher symptom severity scores. Pairwise comparisons of virus associations showed that EACMCV was found in mixed infections more often than expected while ACMV and SACMV were mostly found in single infections. A greater abundance of whiteflies was observed in lowland and coastal areas. Nevertheless, infected cuttings remain the primary source of CMD propagation (95%) in Madagascar.     

Artificial induction of a plant virus protein in transgenic tobacco provides a synchronous system for analyzing the process of leaf chlorosis

The underlying molecular mechanism of chlorosis, a typical symptom of plant viral diseases, remains poorly understood. To establish an experimental system to determine the molecular changes during chlorosis, especially in the early phase, we generated transgenic tobacco plants expressing Cauliflower mosaic virus Transactivator/viroplasmin (Tav) under the control of a chemically inducible promoter. Induction of Tav resulted in visible chlorosis in ten days, a statistically significant decrease in chlorophyll content in two days, decreased expression of chloroplast protein genes, and abnormal thylakoid stacks, indicating that this system reproduces the common features of chlorosis in virus-infected plants.     

大豆花叶病毒引发大豆不同症状的生理特性比较

以接种3个SMV株系后分别表现无症状、花叶和坏死症状的大豆品系浙A8901为材料,研究3类症状叶片的生理指标差异,包括细胞超微结构、H_2O_2积累、水杨酸(SA)含量、光合作用及细胞病毒含量。结果表明:无症状叶片细胞中除叶绿体片层结构轻微扭曲外,其它细胞结构未见异常;CeCl_3标记H_2O_2电镜观察,发现H_2O_2仅在细胞壁外侧少量积累;在接种1d后SA含量较对照显著升高。花叶症状叶片细胞中出现髓鞘状结构和多泡体结构,核膜边缘有染色质凝集现象;细胞壁外侧观察到较多H_2O_2的积累;SA含量在接种后第2 d较对照显著增加。坏死症状叶片中细胞变形严重,细胞器解体,在细胞壁外侧和细胞质中均观察到H_2O_2的大量积累;接种后第2 d SA含量较对照显著增加。三类症状叶片的光合速率、最大光能转化效率(Fv/Fm)和实际光量子效率(ΦPSⅡ)的测定发现,与对照相比均无显著变化。     

Protective role of <Emphasis Type="Italic">S</Emphasis>-methylmethionine-salicylate in maize plants infected with <Emphasis Type="Italic">Maize dwarf mosaic virus</Emphasis>

This study aimed to detect the harmful effects of Maize dwarf mosaic virus (MDMV) infection, and to demonstrate the potential benefits of S-methylmethionine-salicylate (MMS) pretreatment in infected maize (Zea mays L.) plants. The results of chlorophyll a fluorescence measurements showed that in MDMV-infected plants additional quenchers of fluorescence appear, probably as the result of associations between the virus coat protein and thylakoid membranes. It is important to note that when infected plants were pretreated with MMS, such associations were not formed. MDMV infection and MMS pretreatment resulted in a decrease in ascorbate peroxidase (APX) activity in maize leaves, while infection contributed to an increase in activity in the roots. Infection raised the guaiacol peroxidase (GPX) enzyme activity level, which was reduced by MMS pretreatment. MMS contributed to a decrease in both the RNA and coat protein content of MDMV, to an equal extent in maize leaves and roots. The results showed that MMS pretreatment enhanced the stress response reactions against MDMV infection in maize plants and retarded the spreading of infection.     

Salicylic acid alleviates growth inhibition and oxidative stress caused by zucchini yellow mosaic virus infection in Cucurbita pepo leaves

The effects of zucchini yellow mosaic virus (ZYMV) infection and pretreatments with salicylic acid (SA) on biomass accumulation of pumpkin (Cucurbita pepo cv. Eskandarani) were investigated. The response of photosynthesis, transpiration and the activities of antioxidant enzymes in leaves was also considered. Significant reductions in growth parameters (i.e. leaf area, biomass and shoot height), photosynthesis and chlorophyll a and b content were detected in ZYMV-infected leaves in comparison to healthy controls. Antioxidant enzyme activities were increased up to 3-fold for peroxidase (POD), 2-fold for ascorbate peroxidase (APX) and catalase (CAT) activities and 1.3-fold for SOD activity by virus infection. ZYMV infection also caused increases in H₂O₂ and malondialdehyde (MDA) contents. These results suggest that ZYMV infection causes oxidative stress in pumpkin leaves leading to the development of epidemiological symptoms. Interestingly, spraying pumpkin leaves with SA led to recovery from the undesirable effects of ZYMV infection. Leaves treated with 100 μM SA three days before inoculation had the appearance of healthy leaves. No distinct disease symptoms were observed on the leaves treated with 100 μM SA followed by inoculation with ZYMV. In non-infected plants, SA application increased activities of POD and superoxide dismutase (SOD) and inhibited APX and CAT activities.In contrast, SA treatment followed by ZYMV inoculation stimulated SOD activity and inhibited activities of POD, APX and CAT. In addition, MDA displayed an inverse relation, indicating inhibition of lipid peroxidation in cells under SA treatment. It is suggested that the role of SA in inducing plant defense mechanisms against ZYMV infection might have occurred through the SA-antioxidant system. Such interference might occur through inhibition or activation of some antioxidant enzymes, reduction of lipid peroxidation and induction of H₂O₂ accumulation following SA application.     

水稻纹枯病菌毒素致病机理研究

 Crude toxin of Rhizoctonia solani(RS-toxin) caused obvious damage to the cell of rice.The permeability of cell membrane changed and phosphorous permeated exterior when the sheath and leaves were treated with RS-toxin.After 12 hours treated with RS-toxin,chloroplast membrane was damaged and lamella was relaxed and swollen,with some cavities in the chloroplast.Treated with RS-toxin for 36 hours,the chloroplast was disassembled,other organelles became unclear and disappeared such as mitochondria,and some parts of the cell wall thinned and loosed.Treated with 10 times diluted RS-toxin,the chlorophyll content in the rice plants was reduced over 85%.With higher RS-toxin concentration and longer treatment time,the lower the chlorophyll content became.     

华南205木薯二倍体及其同源四倍体对朱砂叶螨取食胁迫的生理响应

为明确木薯同源四倍体抗螨的生理机制,以华南205（South China 205,SC205）木薯的二倍体及其同源四倍体为试验材料,分别于朱砂叶螨Tetranychus cinnabarinus取食胁迫前（取食0 d）及取食胁迫后1、4和8 d观察两个倍性植株叶片的受害情况并测量叶片中叶绿素、游离脯氨酸、丙二醛（malondialdehyde,MDA）、次生代谢物质含量和主要保护酶活性的变化。结果显示,朱砂叶螨取食胁迫后SC205四倍体叶片受害情况较SC205二倍体的轻;取食胁迫后1、4和8 d木薯SC205四倍体叶片中叶绿素含量下降幅度比SC205二倍体的小;取食胁迫后1、4和8 d两个倍性木薯叶片中MDA和游离脯氨酸含量均呈上升的趋势,其中SC205四倍体叶片中MDA含量的上升幅度比SC205二倍体的小,而游离脯氨酸含量的上升幅度比SC205二倍体的大;取食胁迫后1、4和8 d两个倍性木薯叶片中过氧化氢酶（catalase,CAT）、超氧化物歧化酶（superoxide dismutase,SOD）、过氧化物酶（peroxidase,POD）活性和单宁、总酚、总黄酮含量较取食胁迫前均显著上升,且SC205四倍体的上升幅度比SC205二倍体的大。表明木薯同源四倍体植株的抗螨性与叶绿素、游离脯氨酸、MDA、保护酶活性及次生代谢物质含量变化有关,它们均参与了木薯对朱砂叶螨取食胁迫的诱导型防御反应。     

Phytoplasmas change the source–sink relationship of field-grown sweet cherry by disturbing leaf function

Changes in the function of field-grown sweet cherry leaves infected with phytoplasma were evaluated through the analysis of photosynthesis, respiration, carbohydrates and hormones. Phytoplasmal infection caused witches' broom, small leaves, leaf yellowing and leaf rolling. The photosynthesis of infected leaves was considerably reduced, and they were unable to produce sufficient carbohydrates for their own needs. In contrast, the starch content of infected leaves was significantly increased. These results demonstrate the change in the role of infected leaves from sources to sinks. Further analysis revealed that the photosynthetic decline was related to a significant decrease in photosynthetic pigments and to marked inactivation of photosystem II (PSII). Furthermore, the loss of PSII function was due to a decrease in chlorophyll content, reduction and closure of active reaction centers, and decline in photochemical efficiency.