Molecular and biological characterization of a severe isolate of <Emphasis Type="Italic">Tomato chlorotic dwarf viroid</Emphasis> containing a novel terminal right (T<Subscript>R</Subscript>) domain sequence

Tomato chlorotic dwarf viroid (TCDVd) manually inoculated to transgenic (cv.‘Desiree’) potato plants containing antimicrobial cationic peptides failed to develop symptoms in above ground plant parts, but infected tubers were symptomatic. Plants from the infected tubers (second generation plants) emerged as either severely stunted (bushy stunt isolate, BSI) or tall and symptomless. Molecular characterization of BSI isolates showed TCDVd sequence variants 95 to 98% identical to TCDVd sequences from the database, while a viroid variant identical to TCDVd type isolate (acc # AF162131) was cloned from symptomless plants. The TCDVd BSI variants had novel U165C, GU177-178AA, and UCAC181-184CUUU nucleotide substitutions in the terminal right (T_R) domain of the viroid molecule. The cloned viroid cDNAs of the BSI were infectious to experimental (cv. ‘Sheyenne’) tomato plants causing stunted plants with profuse auxiliary shoots. Visual evaluation of the susceptibility of the BSI to 18 potato and 21 tomato cultivars revealed severe symptoms in most cultivars of both species. The progeny variants accumulating in each potato and tomato cultivar exhibited the same novel T_R domain in most cultivars, with only a slight variation in a few. The severity of the stunting symptoms induced by TCDVd from BSI isolates in both potato and tomato cultivars has not been noted previously with other TCDVd isolates and, as such, it is proposed that this new isolate be recognized as a distinct genotype. Emergence of this type of sequence variant in commercial fields or commercial tomato greenhouses could potentially cause relevant losses in both crops.     

Efficacy of Amblyseius largoensis (Muma) as a biocontrol agent of the red palm mite Raoiella indica (Acari: Tenuipalpidae)

Phytoparasitica - The red palm mite, Raoiella indica Hirst (Acari: Tenuipalpidae), is a severe pest of coconut (Cocos nucifera L.), banana (Musa sp.), and some ornamental palms. The predatory mite...     

Damage by Homalinotus depressus in commercial coconut palm crops in the Amazonian region of Brazil

The coconut palm (Cocos nucifera L., Arecaceae) has great economic and social importance for many industrial and non-industrial products. Pests can reduce its productivity and cause its death. In 2005, larvae and adults of a Curculionidae were observed damaging the floral stalk of coconut palms in commercial plantations in the municipality of Moju, Pará State, in the Brazilian Amazon. Insects were identified as the black coconut bunch weevil, Homalinotus depressus (L.) (Coleoptera: Curculionidae: Cholini). This is the first report of this pest damaging coconut palms in Brazil.     

利用两种方法检测苹果锈果类病毒

以克隆ASSVd的部分序列,通过RT-PCR成功合成了地高辛标记的cDNA探针,提取苹果和梨树枝条的总RNA,用斑点杂交技术对其进行了检测试验,结果表明,探针具有很高的灵敏度和特异性。地高辛标记的cDNA探针不与阴性对照枝条RNA以及感染PBCVd、AFCVd、ADFVd枝条总RNA发生杂交,仅与感染ASSVd样品的总RNA杂交。     

Comparison of the ribosomal RNA operon from Texas Phoenix decline and lethal yellowing phytoplasmas

A comparison was made of the two palm yellows phytoplasmas affecting palms to determine if the entire ribosomal RNA operon portion of the phytoplasma genome, or portions thereof, could account for the observed palm host differences. Polymerase chain reaction (PCR) was used to amplify a 5.0?kb DNA fragment consisting of the entire ribosomal RNA operon from a subgroup 16SrIV-D phytoplasma that causes Texas Phoenix palm decline (TPD) in cabbage (Sabal palmetto) palm in west central Florida and from a subgroup 16SrIV-A phytoplasma that causes lethal yellowing (LY) in coconut (Cocos nucifera) palm in Jamaica. Before the PCR reaction, we sequenced by 454 sequencing a draft genome of the coconut LY phytoplasma, strain LYFL, that infects C. nucifera in Florida, and obtained from this draft sequence both copies of the entire ribosomal operon. Sequence analysis of the ribosomal RNA operons from both the LY and TPD phytoplasmas revealed the gene composition and orientation for the operons to be 5′16S rRNA-tRNA^Ile-23S rRNA-5S rRNA3′ and a tRNA^Val3′ downstream of the 5S rRNA gene. Based on molecular comparisons using the sequences of the ribosomal RNA operon, the TPD (16SrIV-D) strain was 98?% similar to the LY (16SrIV-A) strains.     

Detection of the mycoplasma-like organism associated with lethal yellowing disease of palms in Florida by polymerase chain reaction

DNA amplification by polymerase chain reaction (PCR) was used specifically to detect the mycoplasma-like organism (MLO) associated with lethal yellowing disease of palms in Florida. For PCR, a pair of oligonucleotide primers was synthesized according to partial sequences of a cloned 1·3 kbp fragment of lethal yellowing MLO-specific genomic DNA isolated from a diseased windmill palm ( Trachycarpus fortunei ). A DNA product of about 1 kbp was specifically amplified by PCR in reaction mixtures containing template DNA derived from either heart, inflorescence or leaf tissues of lethal yellowing-affected palms. PCR performed for 35 cycles with as little as 5 pg of DNA template, in some instances, was sufficient consistently to amplify the same lethal yellowing MLO DNA product from hearts of 11 species comprising 30 symptomatic palms. Similar reliable and reproducible detection of the lethal yellowing MLO in palm inflorescence spikelets was also achieved after 35 cycles of PCR. When template DNA for PCR was derived from tissues of the the most immature emerging leaf, a 40-cycle reaction was sufficient for consistent foliar detection of the pathogen in all coconut palms including palms with earliest visible symptoms of disease.     

Phytoplasmas associated with disease of coconut in Malaysia: phylogenetic groups and host plant species

Coconut palm ( Cocos nucifera ), oil palm ( Elaeis guineensis ), Bermudagrass ( Cynodon dactylon ) and Madagascar periwinkle ( Catharanthus roseus ) with symptoms indicative of phytoplasma disease were collected from different locations in Malaysia. PCR assays employing phytoplasma universal rRNA gene primers P1/P7 alone or P1/P7 followed by R16F2n/R16R2 detected phytoplasmas in eight out of 20 Malayan Red Dwarf (MRD), nine out of 12 Malayan Yellow Dwarf (MYD) and 12 out of 12 Malayan Tall (MT) coconut palms displaying coconut yellow decline symptoms. Positive detections were also obtained from six out of six oil palm seedlings showing symptoms of yellowing and necrosis, from 10 out of 10 Bermudagrass samples with white leaf symptoms, and from eight out of eight periwinkle plants showing phyllody, virescence, little leaf, proliferation and foliar yellowing. Phytoplasmas were not detected in any of the symptomless plants tested. Sequencing and phylogenetic analysis of PCR products determined that phytoplasmas infecting both MRD and MT coconuts and Bermudagrass in Serdang, Selangor State, were all members of the 16SrXIV ' Candidatus Phytoplasma cynodontis' group, whereas isolates in periwinkle in Serdang were all members of the 16SrI ' Ca. Phytoplasma asteris' group. However, the phytoplasmas detected in MYD coconuts and oil palms from Banting, Selangor State, and in periwinkle from Putrajaya were collectively very similar (99%), but shared <97·5% similarity with 16S rDNA sequences of all other known phytoplasmas, indicating that they represent a novel taxonomic group. Thus, at least two phylogenetically distinct phytoplasmas are associated with the coconut yellow decline syndrome in Malaysia, both of which were also detected in other plant species.     

Fine structure of phloematic trypanosomatid–coconut tree interaction

Phytomonas wilt or Hartrot is a fatal disease of palm (Arecaceae) species including Cocos nucifera (coconut) and is caused by a phloematic trypanosomatid, a promastigote parasite that inhabits phloem sieve elements of disease palms. In the present work, we described the morphology of the interaction between a phloematic trypanosomatid (Phytomonas staheli) and C. nucifera. Two varieties and one ecotype of the adult coconut palm from northeast and southeast Brazil were analyzed, totaling 34,000 plants. Coconut palm losses due to Hartrot varied according to the variety or ecotype and geographic area. Occurrence of Hartrot was insignificant in Rio de Janeiro state (southeast), but in Bahia state (northeast) losses were substantial when appropriate cultural practices were not applied. Symptomatic and healthy palm tissues were analyzed by light and electron microscopy. Laboratory diagnoses revealed the twisted promastigote form of phloematic trypanosomatids in the extracts of shoot apex, leaves, stems and inflorescence in diseased plants, but not in the healthy ones. No parasites were found in the roots. Although the general anatomy of healthy and diseased palms was similar, callose deposition in the sieve plates was revealed by histochemistry and immunocytochemistry in the diseased tissue. Plugging by the P-protein and plastid alterations was also observed. Our observations strongly suggest that parasite traffic between sieve elements took place, although their cell bodies were larger than the sieve pores. Phloematic trypanosomatid proliferation in the sieve tube elements might interrupt the transport of phloem or/and consume plant nutrients. In addition, an association between the percentage of sieve elements colonized by pathogen in palm tissues and disease severity was established.     

Detection of lethal yellowing phytoplasma in embryos from coconut palms infected with Cape St Paul wilt disease in Ghana

This study investigated the potential of seed transmission of Cape St. Paul wilt disease (CSPWD) in coconuts. PCR amplification was used to assess the distribution of phytoplasmas in parts of West African Tall (WAT) palms infected with CSPWD. Employing phytoplasma universal primer pair P1/P7 in standard PCR, or followed with a nested PCR using CSPWD–specific primer pair G813f/AwkaSR, phytoplasma infection was detected in the trunks, peduncles, spikelets, male and female flowers of four infected WAT coconut palms. Through nested PCR, phytoplasma was also detected in four of 19 embryo DNA samples extracted individually from fruits harvested from three of the four infected palms and was confirmed as CSPWD by cloning and sequencing. Subsequently, CSPWD phytoplasma was again detected in five of 33 embryos from nine infected palms, and in one of eight fruits from two symptomless palms. Fruits from infected palms recorded higher percentage germinations in two field nurseries (average of 71·0%) compared to fruits from healthy palms (average of 57·6%), and matured fruits that had dropped from infected palms showed the same levels of germination as those harvested directly from the palms. This indicates that infected fruits retain the ability to germinate whether harvested or dropped. No phytoplasmas were detected in any of the resulting seedlings and plantlets obtained through embryo in-vitro culture. Therefore, although phytoplasma DNA can be detected in embryos, there is as yet no evidence that the pathogen is seed transmitted through to the seedling to cause disease in progeny palms.     

Epidemiological evidence that vegetatively propagated, solanaceous plant species act as sources of Potato spindle tuber viroid inoculum for tomato

In autumn 2006 in the Netherlands, Potato spindle tuber viroid (PSTVd) infections were detected in 42·3 and 71·9% of professionally grown lots of Brugmansia spp. and Solanum jasminoides respectively. The infected lots contained 73 985 and 431 374 plants, respectively, demonstrating the presence of many potential viroid sources for tomato ( Solanum lycopersicum ). PSTVd was identified in cultivars of Brugmansia × candida , B. × flava , B. sanguinea , B. suaveolens and unspecified Brugmansia species/cultivars. Most infected lots of Brugmansia spp. originated from a single Dutch nursery; most infected lots of S. jasminoides originated abroad. Sequence analysis revealed that the PSTVd genomes from Brugmansia spp. contained an average of 360 nt, whereas all genomes from S. jasminoides except one consisted of 357 nt. Furthermore, the collective PSTVd genotypes showed polymorphism at four or more positions, except for two cases in which genotypes from Brugmansia spp. and S. jasminoides were identical. Phylogenetic studies showed that PSTVd genotypes from Brugmansia spp. and S. jasminoides grouped apart from each other and from PSTVd isolates from potato ( Solanum tuberosum ) and Physalis peruviana . The PSTVd genotypes from tomato did not form a separate cluster, but were dispersed over clusters of vegetatively or partly vegetatively propagated plant species, i.e. potato, P. peruviana and S. jasminoides . Moreover, mechanical inoculation of the predominant PSTVd genotypes from S. jasminoides to tomato was successful. These results provide evidence that vegetatively propagated, solanaceous plant species have been sources of infection for tomato crops in the past.     

A set of novel RNAs transcribed from the chloroplast genome accumulates in date palm leaflets affected by brittle leaf disease

Brittle leaf disease or maladie des feuilles cassantes (MFC) is a lethal disorder of date palms that has assumed epidemic proportions in the oases of southern Tunisia. After a prolonged period during which palms are declining, the disease ends with the death of the palms. Whereas no pathogen could ever be associated with the disease, leaflets of affected palms have been previously shown to be deficient in manganese. Analysis of RNA preparations from leaflets of MFC-affected palms revealed the presence of a set of novel RNAs (MFC-RNAs) of sense and antisense polarities, which are homologous to various regions of the date palm chloroplast genome, such as the regions containing genes rrn5S-trnR(ACG) and trnM(CAU)-atpE. In the RNA preparations obtained from leaflets of affected palms, some of these RNAs are present as double-stranded species (MFC-dsRNAs), as witnessed by results from cellulose chromatography, end labeling, RNase digestion, and northern hybridization with strand specific probes. These MFC-RNAs represent a novel type of host-derived RNAs, and their presence in MFC-affected date palms is of diagnostic value.     

“Red Ring” Disease in surinam

In Surinam no red ring disease in coconut, caused by the nematodeRhadinaphelenchus cocophilus, could be found under natural conditions. An inoculation experiment with the nematode in coconut palm and an experiment in oil palm where an entry for the vectorRhynchophorus palmarum was made, resulted in red ring symptoms. Collection of weevils of the speciesR. palmarum in coconut and oil palm plantations and in wild vegetation, showed that both vectors and nematodes occur in considerable numbers. The slow development of red ring in the inoculation experiment and of little leaf — another symptom, caused byR. cocophilus — in a period of excessive drought might give an explanation for the absence of red ring in Surinam. In the main coconut growing areas rainfall is poor as compared with other coconut-growing countries in the Caribbean.     

Local infection associated with vascular bundles: the colonization of coconut palm leaflets by two <Emphasis Type="Italic">Camarotella</Emphasis> species

Two Camarotella (Phyllachoraceae) species, C. torrendiella and C. acrocomiae are the causative agents of small (SV) and large verrucosis (LV), respectively, which are important diseases affecting Brazilian coconut palms. The small verrucosis produces necrotic lesions in coconut palm leaflets, whereas LV just produces chlorosis. Semi-thin sections of asymptomatic leaflets and of leaves presenting stromata in different development stages were compared through light microscopy in order to characterize the colonization process of these two coconut palm verrucosis agents. Camarotella torrendiella initially colonized the adaxial epidermal cells and the cells underlying the epidermis close to the vascular bundles. In latter colonization stages, the hyphae of C. torrendiella remained limited to the underlying necrotic tissue adjacent to the mature stromata, mostly in the intracellular spaces and in the collapsing cells of necrotized tissues around the vascular bundles. This species does not colonize intracellular intact fiber cells, xylem vessels or phloem sieve tube elements. In contrast, C. acrocomiae presented a typical biotrophic parasitism model such as that of some gramineous Phyllachora spp. High densities of C. acrocomiae hyphae were found inside intact sieve tube elements; however, with no evidence of cellular death. The extensive hyphal colonization by C. acrocomiae within sieve tube elements was also observed in tertiary and quaternary bundles, as well as in anastomosing vascular bundles. The dependence of both species on the colonization sites associated with vascular bundles indicates the need for additional studies about these intricate host-pathogen relationships. These studies could be important to define new strategies to control coconut palm verrucosis diseases.     

Comparison of different weed management systems and their effects on yield of coconut plantations in Sri Lanka

The influence of five different weed management systems on nut yield of coconut were evaluated to determine an economical and effective method of controlling weeds in coconut plantations in the low country, dry zone in Sri Lanka. Treatments imposed included slashing and mulching around the palms with slash (T1), slashing and removing the slash (T2), application of glyphosate (N-(phosphonomethyl)-glycine) alone at 1.44 kg ai ha⁻¹ (T3), application of glyphosate alone at 2.88 kg ai ha⁻¹ (T4) and cover cropping with Pueraria phaseoloides (T5). All treatments were applied twice a year, except for the cover cropping treatment, T5. Based on a reduction in weed biomass, treatments T3, T4 and T5 were found to be significantly effective over other treatments. Coconut yield was increased significantly ( P  < 0.05) in glyphosate-applied plots at both tested rates. Control of weeds with the lower concentration of glyphosate (1.44 kg ai ha⁻¹) resulted in a 25% increase in nut yield over the uncontrolled weed plots. At this rate, it was found to be the most effective and economical method of controlling weeds in coconut plantations. Cover cropping with Pueraria phaseoloides was effective in controlling weeds in the long-term, but was not economical compared with the glyphosate application.     

Interactions between citrus viroids affect symptom expression and field performance of clementine trees grafted on trifoliate orange

ABSTRACT Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd), a noncachexia variant of Hop stunt viroid (HSVd), Citrus viroid III (CVd-III), and Citrus viroid IV (CVd-IV) were co-inoculated as two-, three-, four-, and five-viroid mixtures to Clementine trees grafted on trifoliate orange to evaluate their effect on symptom expression, tree growth, and fruit yield. Most trees infected with CEVd-containing viroid mixtures developed exocortis scaling symptoms, as did CEVd alone, whereas most trees infected with HSVd- or CVd-IV-containing mixtures developed bark-cracking symptoms. Trees infected with mixtures containing both CEVd and CVd-IV revealed the existence of antagonism between these two viroids in terms of the expected bark-scaling and cracking symptoms. Synergistic interactions also were identified in trees infected with certain viroid combinations that, in spite of lacking CEVd, expressed exocortis-like scaling symptoms. Viroid interactions also affected the expected response of trees in terms of vegetative growth and fruit yield. Trees infected with viroid combinations containing CEVd or CVd-III were smaller and produced less fruit than trees infected with mixtures not containing these viroids. Viroid interactions on scion circumference and cumulative fruit yield, in terms of additivity of their effects, were statistically confirmed using a factorial analysis of variance model with two mean estimation approaches. In single-viroid infections, CEVd, CVd-III, and, to a lesser extent, CBLVd consistently and significantly reduced tree size and fruit yield. Conversely, HSVd and CVd-IV slightly increased fruit yield and reduced scion circumference. Rare and not consistent significant interactions were detected with the five-, four-, and three-viroid combinations. Antagonistic interactions between CEVd and CVd-III or CBLVd and CVd-III were revealed over the years with consistent significance. The antagonistic interaction between CEVd and CVd-IV was highly significant over the years when additional viroids were present; however, this antagonism appeared much later in the case of an exclusive interaction. HSVd and CVd-IV showed a consistent and significant synergistic interaction on yield only when both viroids were exclusively present. These results demonstrate antagonistic or synergistic relationships between citrus viroids depending on the viroid mixtures present in the host.     

Disease progression of a lethal decline caused by the 16SrIV‐D phytoplasma in Florida palms

Recently, a new phytoplasma was discovered in Hillsborough County in the state of Florida, USA. This phytoplasma belongs to the 16SrIV taxonomic group and is classified as subgroup D. It is the causal agent of lethal bronzing disease (LBD) of palm. Since the discovery of LBD in 2006, the disease has spread throughout much of the state. In 2014 and 2015, stands of cabbage palm and queen palms that had been present at the University of Florida's Fort Lauderdale Research and Education Center in Davie, FL began showing symptoms of LBD. After confirming the presence of the LBD phytoplasma in initially infected palms by nested PCR and RFLP analysis, all palms were systematically sampled over the period of 1 year to monitor and quantify disease spread. A total of 30 cabbage palms were tested monthly by qPCR, with five testing positive on the first sample date. By the end of the study period, 16 cabbage palms had died from the infection. A total of 16 queen palms were surveyed, with three palms initially testing positive. By the end of the study, four queen palms had tested positive and died from the infection. To the authors’ knowledge, this study is the first to document and quantify spread of palm‐infecting phytoplasmas. This data provides important insights into the ecology of palm‐infecting phytoplasmas and highlights the impact that the movement of infective insects can pose to established stands of palms.     

A new disease of greenhouse tomatoes in Israel caused by a distinct strain ofTomato apical stunt viroid (TASVd)

Using the sequential PAGE method for detection of small circular RNA molecules we isolated a viroid from greenhouse-grown tomato plants exhibiting severe stunting in Israel. The viroid was transmitted to tomato and to several other solanaceous plants by graft and mechanical inoculation, but only tomato plants showed symptoms of disease. Cloning and sequencing revealed that the viroid RNA is composed of 363 nucleotides, has 92% identity with the type strain (Ivory Coast strain) ofTomato apical stunt viroid (TASVd) and 99% identity with the Indonesian strain of this viroid. The experimental host range of TASVd-Is differs significantly from that of the type strain of TASVd. The possible epidemiological consequences leading to TASVd spread in geographically distant areas are discussed. http://www.phytoparasitica.org posting Sept. 18, 2002. Corresponding author     

A Review of Fusarium Wilt of Oil Palm Caused by Fusarium oxysporum f. sp. elaeidis

ABSTRACT Vascular wilt is the most destructive disease of oil palm in Africa and causes severe losses in some areas. Symptoms include initial wilting followed by desiccation of the fronds, which finally break and hang around the trunk. Internally, characteristic browning of the vascular elements is seen both in adult palms and in seedlings. Two disease syndromes are commonly seen in the field in adult palms-"acute wilt" where the palm dies within a few weeks and "chronic wilt" where the palm may remain alive for many months and even years but becomes progressively stunted. The pathogen (Fusarium oxysporum f. sp. elaeidis) is a soilborne fungus and the perennial nature of the crop ensured that, in the past, disease management was difficult. Over a period of 30 to 40 years, screening for resistance at the nursery stage was introduced in many plantations and research stations, and successful breeding programs in West Africa, notably in Ivory Coast, have resulted in more resistant oil palm material becoming available. The disease has not yet been detected in South East Asia (largest producer of palm oil) and rigorous quarantine measures have been imposed to prevent introduction of the pathogen into these highly productive areas.