Genotypic diversity of Citrus tristeza virus within red grapefruit,in a field trial site in South Africa

European Journal of Plant Pathology - Grapefruit cultivars (Citrus paradisi Macfad.) are extremely sensitive to Citrus tristeza virus (CTV) infections and are pre-immunized with mild-strain...     

Temporal spore dispersal patterns of grapevine trunk pathogens in South Africa

Trunk disease pathogens of grapevines, viz. Phaeomoniella chlamydospora, Eutypa lata and several species in Botryosphaeriaceae, Phaeoacremonium and Phomopsis are known to infect fresh pruning wounds by means of air-borne inoculum released after rainfall or prolonged periods of high relative humidity. Recent surveys have demonstrated that most or all of these pathogens are present in climatically diverse grape growing regions of South Africa. However, the factors controlling spore dispersal of these pathogens in vineyards were largely unknown. To address this question, spore trapping was done in a Chenin Blanc vineyard in the Stellenbosch area, South Africa, for 14 weeks during the grapevine pruning period from June to mid-September of 2004 and 2005. Hourly recordings of weather data were done by a weather station in the row adjacent to the spore trap. Spores of E. lata and Phomopsis and species in Botryosphaeriaceae were trapped throughout the trapping periods of 2004 and 2005, with higher levels of trapped spores recorded in 2005. The spores of all three pathogens were trapped during or after periods of rainfall and/or high relative humidity. In neither of the 2 years were spores of Pa. chlamydospora or Phaeoacremonium spp. trapped. Results indicated that spore event incidence, as well as the amount of spores released during a spore event of above-mentioned pathogens, were governed by rainfall, relative humidity, temperature and wind speed prior to and during the spore events.     

Genetic diversity of Grapevine rupestris stem pitting-associated virus isolates from Tunisian grapevine germplasm

Grapevine rupestris stem pitting-associated virus (GRSPaV) is one of the most widespread grapevine viruses and is transmitted mainly by grafting. GRSPaV presence was tested in 487 samples representative of the Tunisian grapevine germplasm (including autochthonous, table, wine, wild grape, and rootstock varieties) from different Tunisian regions. GRSPaV infection was detected in 51.3% of samples from different Tunisian regions, among which the table grapevine cultivars were the most commonly infected (68.7%). Genetic variability of GRSPaV isolates from wild and cultivated grapevines was assessed by sequencing the partial capsid protein (CP) gene of 19 Tunisian isolates and 1 Italian GRSPaV isolate from Sicily, and the partial RNA-dependent RNA polymerase (RdRp) gene of 13 Tunisian GRSPaV isolates. According to phylogenetic analysis of CP nucleotide sequences obtained in this study and sequences retrieved from GenBank, Tunisian isolates fell into four phylogenetic groups already described (I, II, III, and IV) and two new phylogenetic groups (VI and VIII). Phylogenetic analysis of the partial RdRp gene revealed that Tunisian isolates of GRSPaV are distributed into four phylogroups. This study highlights the importance of regular monitoring of GRSPaV infections in Tunisia, with special regard to those grapevine accessions employed in conservation and selection programmes. In particular, the presence of new GRSPaV genetic variants and infection of wild grapevines must be taken into account in order to choose a correct control strategy.     

Grapevine leafroll-associated viruses and grapevine virus A in selected Vitis vinifera cultivars in northern Italy

The occurrence of grapevine leafroll-associated virus 1 (GLRaV-1), grapevine leafroll-associated virus 3 (GLRaV-3) and grapevine virus A (GVA) was demonstrated in a viticultural region of northern Italy (Emilia-Romagna) using immunoelectron microscopy. Virus incidence was subsequently assessed using ELISA. A total of 60.6% of the 150 clone selections tested, from 18 local Vitis vinifera cultivars, were found to be infected. ELISA did not reveal the presence of grapevine leafroll-associated virus 2 (GLRaV-2) or grapevine leafroll-associated virus 5 (GLRaV-5). GLRaV-1, GLRaV-3 and GVA were found individually and in various combinations. The most common findings were GLRaV-1 alone (25.3%) and associated with GVA (33%). Serological data confirmed that the majority (91%) of the clones known to be affected by grapevine leafroll (GLR), on its own or in association with rugose wood (RW), contained viruses. On the other hand, where the RW phenomenon was present on its own, only 40% of these clones were ELISA-positive. The implications for the biology of GLR and RW are discussed and the complex aetiology of these grapevine diseases is confirmed.     

Distribution and partial molecular characterization of Grapevine leafroll-associated virus 2 (GLRaV-2) found in Croatian autochthonous grapevine (Vitis vinifera L.) germplasm

Journal of Plant Diseases and Protection - Study of Grapevine leafroll-associated virus 2 (GLRaV-2) distribution was conducted on 13 Croatian autochthonous grapevine cultivars or cultivars which...     

High diversity and clonality are hallmarks of Fusarium circinatum in South Africa

Pitch canker on plantation-grown Pinus species, caused by the fungal pathogen Fusarium circinatum, first appeared in the western and southern Cape regions of South Africa. However, outbreaks have subsequently been reported from the major plantation growing regions of KwaZulu-Natal and Limpopo in the eastern, summer rainfall regions of the country. It is more than 10 years since the last detailed population genetics studies on F. circinatum in the region were conducted. To shed light on the population biology of F. circinatum in this region of South Africa, we used microsatellite markers and mating-type assays to study a collection of 296 isolates from different nurseries and plantation sites. Our results showed that populations in the region are highly diverse, but strongly interconnected, with various genotypes shared across nursery and plantation collection sites. In contrast to nursery populations, those associated with pitch canker outbreaks were characterized by the presence of relatively small numbers of dominant genotypes that were generally widespread across the region. Opposite mating-type individuals occurred in most of the isolate collections, but multilocus linkage disequilibrium analyses pointed towards clonality being the main reproductive mode of F. circinatum in the region. Most of the pathogen's genetic variation could probably have resulted from multiple different introductions into the country and more specifically, into the summer rainfall region. Because the spread and establishment of invasive pathogens are typically driven by aggressive clones, the results of this study provide important considerations for current and future Pinus disease management strategies.     

葡萄浆果内坏死病毒侵染的‘贝达'葡萄cDNA文库构建及其利用

 葡萄浆果内坏死病毒(grapevine berry inner necrosis virus, GINV)侵染葡萄可引起葡萄叶片表现明显的褪绿斑驳症状,其致病的分子机制,特别是病毒与寄主互作蛋白的研究尚未见报道。本研究构建了GINV侵染的‘贝达'葡萄叶片的cDNA文库,并以GINV 外壳蛋白(coat protein,CP)为诱饵筛选文库中与其互作的寄主因子。本研究构建的cDNA文库库容量达1.6×10⁷,插入片段平均大小在1.0 kb以上,质量符合cDNA文库筛库要求。筛选到了55个候选寄主蛋白与GINV CP在酵母中互作。经测序分析及回转验证,结果确定了17个寄主互作蛋白,其涉及叶绿体相关类蛋白、泛素化相关蛋白、防御相关蛋白等。本研究可为深入研究GINV致病性及其与寄主互作机制提供依据。     

Genetic diversity in the 3' terminal 4.7-kb region of grapevine leafroll-associated virus 3

Grapevine leafroll-associated virus 3 (GLRaV-3; Ampelovirus, Closteroviridae), associated with grapevine leafroll disease, is an important pathogen found across all major grape-growing regions of the world. The genetic diversity of GLRaV-3 in Napa Valley, CA, was studied by sequencing 4.7 kb in the 3' terminal region of 50 isolates obtained from Vitis vinifera 'Merlot'. GLRaV-3 isolates were subdivided into four distinct phylogenetic clades. No evidence of positive selection was observed in the data set, although neutral selection (ratio of nonsynonymous to synonymous substitution rates = 1.1) was observed in one open reading frame (ORF 11, p4). Additionally, the four clades had variable degrees of overall nucleotide diversity. Moreover, no geographical structure among isolates was observed, and isolates belonging to different phylogenetic clades were found in distinct vineyards, with one exception. Considered with the evidence of purifying selection (i.e., against deleterious mutations), these data indicate that the population of GLRaV-3 in Napa Valley is not expanding and its effective population size is not increasing. Furthermore, research on the biological characterization of GLRaV-3 strains might provide valuable insights on the biology of this species that may have epidemiological relevance.     

Detection of the German grapevine yellows (Vergilbungskrankheit) MLO in grapevine,alternative hosts and a vector by a specific PCR procedure

A polymerase chain reaction procedure was developed which enables specific amplification of a ribosomal sequence from the mycoplasmalike organism (MLO) associated with German grapevine yellows (Vergilbungskrankheit, VK) and stolbur-related diseases of solanaceous plants. Successful amplification from all samples prepared from various cultivars collected in different viticultural areas indicates that the causal agent is a relatively homogeneous organism. Amplification was also achieved with template DNA prepared from naturally infected weeds in vineyards such asConvolvolus arvensis andSolanum nigrum, and from the planthopperHyalesthes obsoletus that was collected in the vineyards. Feeding of insects of this species on grapevine seedlings resulted in the development of typical yellows symptoms by the grapes.H. obsoletus could therefore be identified as a vector of Vergilbungskrankheit.Abbreviations FD Flavescence dorée - GY Grapevine yellows - MLO Mycoplasmalike organism - PCR Polymerase chain reaction - RFLP restriction fragment length polymorphism - VK Vergilbungskrankheit (German grapevine yellows)     

Characterization of Tomato curly stunt virus: a new tomato‐infecting begomovirus from South Africa

The biological and molecular characterization of a virus recognized as a distinct begomovirus species, Tomato curly stunt virus (ToCSV), first observed in South Africa in 1997, is reported here. Whitefly‐transmission and host‐range studies were carried out using a Bemisia tabaci colony identified as the B‐biotype. The experimental host range of ToCSV spanned primarily species in the Solanaceae and Fabaceae. The complete ToCSV genome (2·766 kb) was amplified by PCR, cloned, and the DNA sequence determined. Phylogenetic analysis revealed that ToCSV was most closely related to Tobacco leaf curl Zimbabwe virus (TbLCZV), at 84% nucleotide identity, indicating that ToCSV is a new species in the genus Begomovirus that is probably endemic to southern Africa. The ToCSV genome sequence contained all of the hallmark coding and non‐coding features characteristic of other previously recognized monopartite begomoviruses. ToCSV is only the second begomovirus described from southern Africa that infects solanaceous species. Neither a begomoviral DNA‐B component nor a satellite‐like DNA molecule was detected by PCR in extracts of ToCSV‐infected plants.     

从德国虞美人花卉中检测到李痘病毒

虞美人(ＰａｐａｖｅｒｒｂｏｅａｓＬ.)为罂粟科的常见栽培花卉植物。采集自世博会德国园的虞美人(ＰａｐａｖｅｒｒｂｏｅａｓＬ.)病株,表现明显的细花叶症状,具有典型的病毒病症状。因而我们采用电镜负染,生物接种实验,初步认为侵染德国虞美人引起花叶的病原为李痘病毒(Ｐｌ     

Distribution and genetic diversity of root‐knot nematodes (Meloidogyne spp.) in potatoes from South Africa

A molecular‐based assay was employed to analyse and accurately identify various root‐knot nematodes (Meloidogyne spp.) parasitizing potatoes (Solanum tuberosum) in South Africa. Using the intergenic region (IGS) and the 28S D2–D3 expansion segments within the ribosomal DNA (rDNA), together with the region between the cytochrome oxidase subunit II (COII) and the 16S rRNA gene of the mtDNA, 78 composite potato tubers collected from seven major potato growing provinces were analysed and all Meloidogyne species present were identified. During this study, M. incognita, M. arenaria, M. javanica, M. hapla, M. chitwoodi and M. enterolobii were identified. The three tropical species M. javanica, M. incognita and M. arenaria were identified as the most prevalent species, occurring in almost every region sampled. Meloidogyne hapla and M. enterolobii occurred in Mpumalanga and KwaZulu‐Natal, respectively, while M. chitwoodi was isolated from two growers located within the Free State. Results presented here form part of the first comprehensive surveillance study of root‐knot nematodes to be carried out on potatoes in South Africa using a molecular‐based approach. The three genes were able to distinguish various Meloidogyne populations from one another, providing a reliable and robust method for future use in diagnostics within the potato industry for these phytoparasites.     

Viruses and virus diseases of grapevine in Tunisia

Mature canes were collected from vines in the main grapevine-growing areas in Tunisia (Cape Bon, Bizerte, Ben Arous), from commercial vineyards and mother-plant plots, to assess the presence of virus and virus-like diseases. Biological (mechanical transmission onto herbaceous hosts and grafting onto indicator woody plants) and serological detection (ELISA) methods were applied. ELISA showed that 96.4% of 669 vines tested were infected, most of them (88.1%) by at least two viruses. Grapevine leafroll-associated 3 closterovirus (GLRaV-3) was the most widespread virus (87.9%), followed by grapevine A vitiviras (GVA, 69.4%), grapevine fleck virus (GFkV, 51.9%), grapevine leafroll-associated 1 closterovirus (GLRaV-1, 36.8%), grapevine leafroll-associated 2 closterovirus (GLRaV-2, 19.1%), grapevine fan leaf nepovirus (GFLV, 18.2%) and grapevine B vitiviras (GVB, 14.8%). ELISA tests yielded negative results for grapevine leafroll-associated 7 closterovirus (GLRaV-7) and potato X potexvirus (PVX). The highest infections were found in Bizerte and Cape Bon regions (100 and 99.2%), and in vineyards aged over 20 years (98.5%) as compared with the younger ones (81.1%). Rootstocks in mother-plant plots were practically free from all the viruses tested (1 plant infected out of 81), whereas severe infections were found in Vitis vinifera mother plants (67.4% of 341 samples), in particular table grapes (92.6%) compared with wine grapes (47.9%). In these mother-plant plots, the prevailing viruses were GLRaV-3 (41.3%), followed by GFkV (36.7%), GVA (27.9%), GLRaV-1 (17%) and GLRaV-2 (15.2%). GFLV and GVB were far more limited (1.5 and 0.6%, respectively). The presence of vein necrosis and vein mosaic was ascertained by transmission onto 110R and Vitis riparia indicators, whereas only GFLV was mechanically transmitted onto herbaceous hosts (from about 20% of the samples).     

Viruses and virus diseases of grapevine in Palestine

Surveys were carried out in vineyards in the main grapevine-growing areas of Palestine (Hebron, Bethlehem, Gaza, Jerusalem, Ramallah, Jenin, Jericho and Nablus) to assess the presence and incidence of virus and virus-like diseases. Leafroll symptoms were observed in Bethlehem, Ramallah and Jerusalem in native and imported cultivars, with higher rates in the red-fruited Shami, Beitoni and Smari. Rugose-wood symptoms were also observed in local and foreign cultivars, especially on grafted vines with a high incidence in Bethlehem. Fanleaf symptoms were rarely observed, while phytoplasma-induced symptoms were observed in Jenin, Jericho and Bethlehem on cvs Biadi, Superior Seedless and Beitoni. ELISA tests showed that 463 out of 566 (82%) tested vines were infected by at least one virus. GVA was the prevailing virus (66.1%), followed by GLRaV-1 (45.6%), GLRaV-3 (21.7%), GFkV (15.7%) and GLRaV-2 (8.3%). GVB and GFLV were also detected to a lesser extent, their incidence ranging between 3.7 and 1.2%, whereas GLRaV-7 was detected in a single vine of cv. Sultanina of foreign origin. Vineyards in the Bethlehem area were particularly badly damaged (97.5%), and some local cultivars were totally (Jandali, Marrawi and Shoyoukhi) or heavily infected (Zaini, Biadi and Shami). ELISA testing of 69 young rootstock mother plants showed a relatively high incidence of virus infection (20.3%). Vein necrosis and vein mosaic diseases were also ascertained on graft-inoculated 110R and Vitis riparia indicator plants, whereas no viruses other than GFLV were mechanically transmitted from about 200 vines onto inoculated herbaceous hosts.     

Viruses and virus diseases of grapevine in Egypt

Surveys for virus and virus-like diseases were carried out in commercial vineyards of the main grapevine-growing areas of Egypt along the river Nile and in recently reclaimed desert lands. The only symptoms observed and identified with reasonable confidence in the field were those of leafroll disease in red-berried cultivars. No virus was transmitted to herbaceous hosts by mechanical inoculation from glasshouse-forced cuttings of about 300 vines (40% of total samples). By contrast, ELISA tests showed that 78% of the assayed European vines (521 out of 664) were infected by one (29%) or more (49%) viruses. Grapevine virus A (GVA) was the most widespread virus (67.9% infection), followed by Grapevine leafroll-associated virus 3 (GLRaV-3) (55.9% infection). All the other viruses tested for were scarcely represented, i.e. Grapevine leafroll-associated virus 1 (GLRaV-1) 1.8% infection, Grapevine leafroll-associated virus 2 (GLRaV-2) 1.4% infection, Grapevine virus B (GVB) (0.6% infection) and Grapevine fleck virus (GFkV) (0.2% infection), or, like Grapevine fanleaf virus (GFLV), were totally absent. The infection rate of native cultivars (86%) was particularly heavy. 'Banaty Abiad' and 'Romy Ahmer', the two major Egyptian cultivars, had infection levels of 78% and 89%, respectively, and 'Fayoumy', the most important cultivar in the Fayoum area, had 96% infection. Totally infected were the tested samples of several minor native cultivars such as 'Farg El-Tair', 'Siwi Abiad', 'Ta'afi', 'Romy Abiad', 'Eswid El-Wady', 'Edkawy' and 'Bez El-Anza'. Slightly better was the sanitary situation of imported European grapevine cultivars (60% infection) and of American rootstocks (11.5% infection). In rootstocks, infection rate by GVA and GLRaV-3 was 5.5%, whereas GVB and GLRaV-1 were only sporadically detected.     

Viruses and virus diseases of grapevine in Lebanon

Grapevines were surveyed for the presence of virus and virus-like diseases in the main viticultural areas of Lebanon (Bekaa valley, Mount Lebanon, South and North Lebanon). Symptoms of rugose wood were observed in vines ofall cultivars and areas surveyed, whereas leafroll was observed only in some vineyards of the Bekaa valley and, to a lesser extent, in South Lebanon on cvs Tfaifihi, Cinsaut and Cardinal. Symptoms of fanleaf and of phytoplasma-induced yellows were also observed with low frequency in the Bekaa valley on wine-grape cultivars. ELISA tests showed that 53% of 1536 Vitis vinifera vines individually checked were infected by one or more viruses. Grapevine trichovirus A (GVA) was the prevailing virus (32.4%), followed by grapevine fleck virus (GFkV) (19.5%) and grapevine leafroll-associated closterovirus 3 (GLRaV-3) (12.4%). Grapevine leafroll-associated closterovirus 1 (GLRaV-l), grapevine trichovirus B (GVB) and grapevine fanleaf nepovirus (GFLV) were also detected to a lesser extent, their incidence ranging between 1.1 and 3.6%.     

Viral sanitary status of declining grapevine Syrah clones and genetic diversity of Grapevine Rupestris stem pitting-associated virus

In order to determine the etiology of Syrah decline, virus detection was performed on 22 Syrah clones, chosen for their various levels of sensitivity to Syrah decline. All clones, including the sensitive ones, were free of 20 main grapevine viruses. In contrast, Grapevine Syrah virus-1 and Grapevine Rupestris stem pitting-associated virus (GRSPaV), were detected in 56 % and 100 % of the analysed Syrah clones respectively. This is the first report of GSyV-1 in a French vineyard. The genetic diversity of a 380 nt region within the GRSPaV coat protein gene was studied extensively in vines differing in their sensitivity to Syrah decline. Most GRSPaV variants were scattered between the four phylogenetic groups previously identified; 65 % of the sequences analysed were found to belong to the GRSPaV—group 1, 22 % to—group 2b, 10 % to—group 2a and 2 % to—group 3. Seventy percent of the 31 plants analysed harboured mixtures of genomic variants. Statistical analyses revealed no significant correlation between sensitivity and GRSPaV sequence variation. This suggests that GRSPaV is not the direct etiological agent of the Syrah decline.     

Management of nematodes and a stalk borer by increasing within-field sugarcane cultivar diversity

The aim of this study was to determine whether an increase in plant diversity could modify the structure of the nematode community in favour of less pathogenic species and whether it affected the lepidopteran stalk borer, Eldana saccharina . Four sugarcane cultivars were planted either singly or as a mixture in the furrow. Nematodes were enumerated when the crops were 6 months old for five successive 10 to 13 month old crop cycles. Results showed that the mixture of cultivars had little significant impact on the overall abundance of the plant-parasitic or free-living nematodes. However, the nematode community structure within the mixture was slightly different to that observed on any single cultivar planted on its own and there was a higher than expected proportion of Helicotylenchus dihystera during the first three crops. With successive crops and in all treatments, there was an overall trend of increasing proportions of Meloidogyne javanica in the nematode community. However, the way that the change in the species-balance occurred in the mixed cultivar plots suggested a resistance to the evolving dominance of M. javanica . These results showed that sugarcane cultivars interacted within the rhizosphere when planted in a mixture because the observed nematode community in the mixture differed from that expected. The level of damage caused by E. saccharina was slightly lower in the mixture than expected from the actual cultivar composition.