Phylogenetic relationships of coconut phytoplasmas and the development of specific oligonucleotide PCR primers

Using the polymerase chain reaction the 16S rRNA genes and the 16S-23S spacer regions of phytoplasmas associated with lethal decline diseases of coconut palm (Cocos nucifera), were amplified from infected plants from Florida and the Yucatan region in Mexico and from east and west Africa. Following sequencing of the rDNA products, phylogenetic analysis confirmed that these coconut phytoplasmas form a separate cluster within the phytoplasma clade and that the pathogen causing diseases in west Africa formed a new sub-clade within this cluster. Analysis of the 16S-23S intergenic spacer regions confirmed the sequence diversity of this region and enabled two primers to be designed which were specific for the diseases found in east and west Africa. None of these specific primers, when paired with a universal primer, produced PCR amplification products from healthy coconut DNA, infected coconut DNA from the Caribbean or DNA from a variety of periwinkle (Catharanthus roseus)-maintained phytoplasmas. These specific primers can serve as effective tools for identifying particular coconut phytoplasmas in field samples.     

16S rRNA interoperon sequence heterogeneity distinguishes strain populations of palm lethal yellowing phytoplasma in the Caribbean region

DNA of phytoplasmas in lethal yellowing (LY)‐diseased palms was detected by a nested polymerase chain reaction (PCR) assay employing rRNA primer pair P1/P7 followed by primer pair LY16Sf/ LY16‐23Sr. Polymorphisms revealed by Hinfl endonuclease digestion of rDNA products differentiated coconut‐infecting phytoplasmas in Jamaica from those detected in palms in Florida, Honduras and Mexico. A three fragment profile was generated for rDNA from phytoplasmas infecting all 21 Jamaican palms whereas a five fragment profile was evident for phytoplasmas infecting the majority of Florida (20 of 21), Honduran (13 of 14) and Mexican (5 of 5) palms. The RFLP profile indicative of Florida LY phytoplasma was resolved by cloning into two patterns, one of three bands and the other of four bands, that together constituted the five fragment profile. The two patterns were attributed to presence of two sequence heterogeneous rRNA operons, rrnA and rrnB, in most phytoplasmas composing Florida, Honduran and Mexican LY strain populations. Unique three and four fragment RFLP profiles indicative of LY phytoplasmas infecting Howea forsteriana and coconut palm in Florida and Honduras, respectively, were also observed. By comparison, the Jamaican LY phytoplasma population uniformly contained one or possibly two identical rRNA operons. No correlation between rRNA interoperon heterogeneity and strain variation in virulence of the LY agent was evident from this study.     

Molecular identification of ‘Candidatus Phytoplasma palmicola’ associated with coconut lethal yellowing in Equatorial Guinea

During the past two decades, a high mortality of coconut palms was observed in the coastal areas of Equatorial Guinea. Reportedly, the palm population has been reduced by 60%–70%, and coconut production has decreased accordingly. To identify the cause of the mortality, a survey was carried out in April 2021 in various localities of the coconut belt. Molecular analyses carried out on 16S rRNA and secA genes detected phytoplasma presence in the majority of the samples. Sequencing and BLAST search of the 16S rRNA gene sequences showed >99% identity of the detected phytoplasmas to ‘Candidatus Phytoplasma palmicola’. The RFLP analyses of 16S ribosomal gene using Tru1I and TaqI enzymes led to assign these phytoplasmas to subgroup 16SrXXII-A. In all samples that tested positive, including one from a hybrid coconut palm and two from oil palm the same phytoplasma was identified. The phylogenetic analyses of 16S rRNA and secA genes confirmed respectively 99.98%–100% and 97.94%–100% identity to ‘Ca. P. palmicola’. RFLP analyses using MboII enzyme on the secA gene amplicon differentiated the phytoplasma found in Equatorial Guinea from those present in Ghana and Ivory Coast. The Equatorial Guinean phytoplasma strain resulted to be identical to the strains from Mozambique, confirming the presence of a geographic differentiation among phytoplasma strains in the coastal areas of Western and Central Africa. The identified phytoplasma is different from the ‘Ca. P. palmicola’ strains found in Ghana and Ivory Coast and represents the first identification a 16SrXXII-A strain in Equatorial Guinea and in Central Africa. Strict monitoring and surveillance procedures for early detection of the pathogen are strongly recommended to reduce its impact and further spread in the country and permit the recovery of coconut plantations.     

Lethal yellowing-type diseases of palms associated with phytoplasmas newly identified in Florida, USA

A nested polymerase chain reaction (PCR) assay was used to detect phytoplasmas in stem tissues from declining silver date ( Phoenix sylvestris ), Canary Island date ( Phoenix canariensis ), edible date ( Phoenix dactylifera ), Queen ( Syagrus romanozoffiana ) and Mexican fan ( Washingtonia robusta ) palms, all displaying symptoms similar to lethal yellowing (LY) disease, in a tri-county region of west central Florida. Restriction fragment length polymorphism analysis or sequencing of PCR-amplified rDNA products (1.6 kb) identified three distinct group 16SrIV phytoplasma strains among 38 infected palms. Most palms (86.8%) contained Texas Phoenix decline (TPD) phytoplasma, a subgroup 16SrIV-D strain, while two P. canariensis harboured palm LY phytoplasma, a subgroup 16SrIV-A strain. A novel phytoplasma, initially detected in W. robusta and tentatively classified as a subgroup 16SrIV-F strain, also occurred with LY phytoplasma as mixed infections in two P. dactylifera palms. Collectively, these findings extend the known geographic range of TPD in the USA to include Florida and the listing of TPD-susceptible palm species to include P. dactylifera , P. sylvestris and S. romanozoffiana . Moreover, discovery of a novel subgroup 16SrIV-F strain in W. robusta adds to the list of phytoplasma host palm species and complexity of phytoplasma-vector-palm pathosystems newly identified in the west central region of the state. The emergence of new lethal disease of palms beyond southern subtropical region of the state is unprecedented but follows similar developments in other regions where LY is known to occur.     

Detection and Identification of Aster Yellows Phytoplasma Associated with Lipstick Yellow Frond Disease in Malaysia

Yellowing symptoms similar to coconut yellow decline phytoplasma disease were observed on lipstick palms (Cyrtostachys renda) in Selangor state, Malaysia. Typical symptoms were yellowing, light green fronds, gradual collapse of older fronds and decline in growth. Polymerase chain reaction assay was employed to detect phytoplasma in symptomatic lipstick palms. Extracted DNA was amplified from symptomatic lipstick palms by PCR using phytoplasma‐universal primer pair P1/P7 followed by R16F2n/R16R2. Phytoplasma presence was confirmed, and the 1250 bp products were cloned and sequenced. Sequence analysis indicated that the phytoplasmas associated with lipstick yellow frond disease were isolates of ‘Candidatus Phytoplasma asteris’ belonging to the 16SrI group. Virtual RFLP analysis of the resulting profiles revealed that these palm‐infecting phytoplasmas belong to subgroup 16SrI‐B and a possibly new 16SrI‐subgroup. This is the first report of lipstick palm as a new host of aster yellows phytoplasma (16SrI) in Malaysia and worldwide.     

Zophiuma lobulata (Hemiptera: Lophopidae) causes Finschhafen disorder of coconut and oil palms

Finschhafen disorder (FD) affects coconut and oil palms in Papua New Guinea (PNG). It is characterised by yellow‐bronzing of fronds which begins at the tips and progresses towards the petiole. Although the planthopper Zophiuma lobulata (Hemiptera: Lophopidae) has been posited as a cause of FD, the basis of the relationship has not been established. Studies conducted previously on FD predate the availability of DNA‐based techniques to test for the involvement of plant pathogens such as phytoplasmas that cause yellows‐type diseases in many plant taxa and are transmitted by the order of insects to which Z. lobulata belongs. In this study, polymerase chain reaction (PCR) assays found no evidence of phytoplasmas or bacteria‐like organisms (BLOs) in tissues of coconut and oil palm symptomatic for FD and from Z. lobulata feeding on these plants. Further studies involved releasing Z. lobulata adults and nymphs onto caged, potted coconut and oil palms and onto palm fronds enclosed in mesh sleeves. In both experiments, chlorotic symptoms on the palms were observed in the presence of Z. lobulata. Insect‐free control palms did not exhibit chlorotic symptoms of FD. In the frond sleeve experiment, only the fronds where Z. lobulata fed developed chlorosis indicating that the disorder is not systemic. Unlike most yellows‐type diseases associated with Hemiptera, this study indicates that FD is because of a direct feeding effect on palms by Z. lobulata rather than transmission of a pathogen.     

Occurrence of 16SrIV Subgroup A Phytoplasmas in Roystonea regia and Acrocomia mexicana Palms with Lethal Yellowing‐like Syndromes in Yucatán,Mexico

The lethal yellowing (LY) disease and LY‐type syndromes affecting several palm species are associated with 16SrIV phytoplasmas in the Americas. In Mexico, palms of the species Roystonea regia and the native Acrocomia mexicana were found to exhibit LY‐type symptoms, including leaf decay, starting with mature leaves, necrosis and atrophy of inflorescences. DNA extracts obtained from these palms could be amplified by nested‐PCR using phytoplasma‐universal primer pair P1/P7 followed by LY‐group‐specific primer pair LY16Sr/LY16Sf. Blast analysis of the sequences obtained revealed an identity of 100% for R. regia and 99.27% for A. mexicana with 16SrIV‐A strain associated with LY in Florida, USA (Acc. AF498309 ). Computer‐simulated RFLP analysis showed that the patterns for the phytoplasma DNA of the two palm species were highly similar to that for 16SrIV subgroup A strain. A neighbour‐joining tree was constructed, and the sequences of the two palm species clustered in the same clade of group 16SrIV subgroup A. The results therefore support that LY‐type syndromes observed in palms of R. regia and A. mexicana in the Yucatan region of Mexico are associated with 16SrIV subgroup A phytoplasmas.     

Cloning and Sequencing of Phytoplasma Ribosomal DNA (rONA) Associated with Kerala Wilt Disease of Coconut Palms

Using the polymerase chain reaction (PCR) the 165 rRNA gene of phytoplasma associated with Kerala wilt disease of coconut palm (Cocos nucifera L) was amplified from infected leaf samples. Within the three universal primer pairs P1/P6, P1/P7and P41 P7, the primer pair P4/P7 only showed an amplification of 650 bp DNA fragment. 5ince P4/P7 amplifies the 16S-23S intergenic spacer region of 165 rRNA gene, the PCR product 650 bp of Kerala wilt disease palm indicates the phytoplasma DNA. The amplified fragment was sequenced and deposited in Genbank data library (Accession No. AY158660). The absence of restriction sites for Bcll and Rsa/l in 650 bp indicates phytoplasmic nature of DNA and its strain difference. A comparison of the 650 bp sequence with other phytoplasmas and its restriction profile indicates Kerala wilt disease phytoplasma as a separate 165 rRNA group in the classification of phytoplasmas. To our knowledge, this report records the first finding of the phytoplasma DNA using universal primers and its sequence analysis in coconut palms of Kerala, south India.     

Molecular study of two distinct phytoplasma species associated with streak yellows of date palm in Iran

A disease with symptoms similar to palm lethal yellowing was noticed in the early 2013 in Khuzestan Province (Iran) in date palm (Phoenix dactylifera). Infected trees displaying symptoms of streak yellows and varied in the incidence and severity of yellowing. A study was initiated to determine whether phytoplasma was the causal agent. Polymerase chain reaction–restriction fragment length polymorphism (PCR‐RFLP) methods using universal phytoplasma primers pairs R16mF1/mR1 and M1/M2 were employed to detect putative phytoplasma(s) associated with date palm trees. Nested PCR using universal primers revealed that 40 out of 53 trees were positive for phytoplasma while asymptomatic date palms from another location (controls) tested negative. RFLP analyses and DNA sequencing of 16S rDNA indicated that the presence of two different phytoplasmas most closely related to clover proliferation (CP) phytoplasma (group 16SrVI) and ash yellows (AY) phytoplasma (group 16SrVII). Sequence analysis confirmed that palm streak yellows phytoplasmas in each group were uniform and to be phylogenetically closest to “CandidatusP. fraxini” (MF374755) and “Ca. P. trifolii” isolate Rus‐CP361Fc1 (KX773529). Result of RFLP analysis of secA gene of positive samples using TruI and TaqI endonuclease is in agreement with rDNA analysis. On this basis, both strains were classified as members of subgroups 16SrVI‐A and 16SrVII‐A. This is the first report of a phytoplasma related to CP and AY phytoplasma causing date palm yellows disease symptoms.     

Comparative PCR analyses for the detection of the Cape St. Paul wilt disease phytoplasma in coconut palms in Ghana

Cape St. Paul Wilt Disease (CSPWD), the Ghanaian form of the lethal yellowing‐type diseases associated with phytoplasmas, is yet the major factor affecting the coconut industry in Ghana since 1932. Recently, a PCR assay based on a non‐ribosomal gene sequence was developed for the detection of the CSPWD phytoplasma in the West Region. Our study aimed at comparing the performance of the non‐ribosomal PCR to existing ribosomal PCRs and determine the best assay to use for the detection of the CSPWD phytoplasma within the three major coconut‐growing regions: Central, Western and Volta and in palms at different ages and disease stages. To determine the most affected region, 163 CSPWD‐affected coconut palms from 32 locations from the Central, Western and Volta Regions were randomly sampled. The analysis of the presence of the CSPWD phytoplasma in coconut palms of different ages showed that palms within the age brackets (1–10), (11–20) and (61–70) years were the most affected by CSPWD. The disease was most widespread in the Central, followed by the Western, then the Volta Region. A Euclidean similarity analysis of the infection rate across palm ages revealed three distinct clusters at a linkage distance of 6.5. The PCR assay based on the secA gene sequence yielded the highest number of coconut palms positive for the CSPWD phytoplasma compared to PCR assays targeting phytoplasma ribosomal genes. These results report an update on the detection of the CSPWD phytoplasma in the CSPWD‐affected coconut regions and across coconut palms representing different ages and disease stages and provide valuable information to support the CSPWD management in Ghana.     

Molecular Characterization of 16S Ribosomal DNA and Phylogenetic Analysis of Two X-disease Group Phytoplasmas Affecting China-tree (Melia azedarach L.) and Garlic (Allium sativum L.) in Argentina

Two phytoplasmas closely related to the X‐disease group were associated with China‐tree (Melia azedarach L.) and garlic (Allium sativum L.) decline diseases in Argentina. The present work was aimed at studying their phylogenetic relationship based on molecular characterization of the 16S ribosomal DNA sequences. Phytoplasma DNAs were obtained from naturally infected China‐tree and garlic plants from different geographical isolates. The results from analysis of restriction fragment length polymorphisms and nucleotide sequences of the 16S rDNA showed the affiliation of China‐tree and garlic decline phytoplasmas to the 16SrIII (X‐disease group), subgroups B and J, respectively. Both organisms had high sequence similarities in the 16SrDNA nucleotide sequence with the Chayote witches’ broom phytoplasma from Brazil. The phylogenetic tree, constructed by parsimony analysis, grouped the Garlic decline, China‐tree decline, Chayote witches’ broom and Clover yellow edge phytoplasmas into a cluster separated from the other phytoplasmas of the X‐disease group.     

Further studies on a spiroplasma isolated from coconut palms in Jamaica

The pathogenicity of a spiroplasma isolated from coconut palms was tested by (1) transmission experiments to palms and other plants susceptible to infection by mycoplasmas, using the suspected vector of lethal yellowing, Myndus crudus, and vectors of the agents of other yellows diseases and (2) enzyme-linked immunosorbent assay (ELISA) to detect spiroplasma antigens in diseased palm tissues. Results of both these tests were negative and, as earlier attempts to repeat the isolations from lethal yellowing diseased palms had also been unsucessful, it was concluded that this organism was not the causal agent of lethal yellowing disease. Further analysis by serological tests and by polyacrylamide gel electrophoresis (PAGE) of spiroplasma proteins confirmed that the coconut isolates were related to members of the Spiroplasma citri serogroup but were distinct from other strains tested.     

Association of a phytoplasma with a yellow leaf syndrome of sugarcane in Africa

Evidence is presented for the association of a phytoplasma, provisionally named sugarcane yellows phytoplasma (ScYP), in sugarcane affected by a yellow leaf syndrome. The phytoplasma was consistently detected in leaves of more than 40 varieties from eight African countries. It was present in all symptomatic as well as some asymptomatic field grown cane samples but not in plants grown from true seed, and it was also observed in phloem sieve tubes by transmission electron microscopy. Phytoplasma 16S rDNA was confirmed by PCR, and restriction fragment analysis using Rsal and Haelll confirmed that PCR-amplified products were of phytoplasma rather than of plant or of other pathogen origin. Sequences obtained from the intergenic spacer region, between the 16S and 23S rDNA genes, confirmed the identity of the phytoplasma as belonging to the western X group of phytoplasmas.     

Sequence Analysis of 16S rRNA and secA Genes Confirms the Association of 16SrI‐B Subgroup Phytoplasma with Oil Palm (Elaeis guineensis Jacq.) Stunting Disease in India

During January 2010, severe stunting symptoms were observed in clonally propagated oil palm (Elaeis guineensis Jacq.) in West Godavari district, Andhra Pradesh, India. Leaf samples of symptomatic oil palms were collected, and the presence of phytoplasma was confirmed by nested polymerase chain reaction (PCR) using universal phytoplasma‐specific primer pairs P1/P7 followed by R16F2n/R16R2 for amplification of the 16S rRNA gene and semi‐nested PCR using universal phytoplasma‐specific primer pairs SecAfor1/SecArev3 followed by SecAfor2/SecArev3 for amplification of a part of the secA gene. Sequencing and BLAST analysis of the ～1.25 kb and ～480 bp of 16S rDNA and secA gene fragments indicated that the phytoplasma associated with oil palm stunting (OPS) disease was identical to 16SrI aster yellows group phytoplasma. Further characterization of the phytoplasma by in silico restriction enzyme digestion of 16S rDNA and virtual gel plotting of sequenced 16S rDNA of ～1.25 kb using iPhyClassifier online tool indicated that OPS phytoplasma is a member of 16SrI‐B subgroup and is a ‘Candidatus Phytoplasma asteris’‐related strain. Phylogenetic analysis of 16S rDNA and secA of OPS phytoplasma also grouped it with 16SrI‐B. This is the first report of association of phytoplasma of the 16SrI‐B subgroup phytoplasma with oil palm in the world.     

Loop mediated isothermal amplification (LAMP) assay for detection of coconut root wilt disease and arecanut yellow leaf disease phytoplasma

The coconut root wilt disease (RWD) and the arecanut yellow leaf disease (YLD) are two major phytoplasma associated diseases affecting palms in South India. Greatly debilitating the palm health, these diseases cause substantial yield reduction and economic loss to farmers. A rapid and robust diagnostic technique is crucial in efficient disease management. We established phytoplasma 16S rDNA targeted loop mediated isothermal amplification (LAMP) and real time LAMP based diagnostics for coconut RWD and arecanut YLD. The LAMP reaction was set at 65 °C and end point detection made using hydroxynaphthol blue (HNB) and agarose gel electrophoresis. Molecular typing of LAMP products were made with restriction enzyme HpyCH4 V. Conventional PCR with LAMP external primers and sequencing of amplicons was carried out. Real time LAMP was performed on the Genei II platform (Optigene Ltd., UK). An annealing curve analysis was programmed at the end of the incubation to check the fidelity of the amplicons. The phytoplasma positive samples produced typical ladder like bands on agarose gel, showed colour change from violet to blue with HNB and produced unique annealing peak at 85 ± 0.5 °C in the real time detection. Restriction digestion produced predicted size fragments. Sequencing and BLASTN analysis confirmed that the amplification corresponded to phytoplasma 16S rRNA gene. LAMP method devised here was found to be more robust compared to conventional nested PCR and hence has potential applications in detection of phytoplasma from symptomatic palm samples and in rapid screening of healthy seedlings.     

Detection and differentiation of the coconut lethal yellowing phytoplasma in coconut‐growing villages of Grand‐Lahou,Côte d'Ivoire

Surveys for the Côte d'Ivoire lethal yellowing (CILY) phytoplasma were conducted in eight severely CILY‐affected villages of Grand‐Lahou in 2015. Leaves, inflorescences and trunk borings were collected from coconut palms showing CILY symptoms and from symptomless trees. Total DNA was extracted from these samples and tested by nested polymerase chain reaction/RFLP and sequence analysis of the 16S rRNA, ribosomal protein (rp) and the translocation protein (secA) genes. The CILY phytoplasma was detected in 82.9% of the symptom‐bearing palms collected from all the surveyed villages and from all the plant parts. Trunk borings were recommended as the most suitable plant tissue type for sampling. Results indicate that the CILY phytoplasma may have a westward spread to other coconut‐growing areas of Grand‐Lahou. CILY phytoplasma strains infecting coconut palms in the western region of Grand‐Lahou exhibited unique single nucleotide polymorphisms on the rp sequence compared to the strains from the eastern region. Moreover, single nucleotide polymorphisms on the SecA sequence distinguished the CILY phytoplasma from the Cape St. Paul Wilt Disease phytoplasma in Ghana, and the Lethal Yellowing phytoplasma in Mozambique.     

Detection and Characterization of Phytoplasmas Infecting Ornamental and Weed Plants in Iran

During field surveys in 2004, ornamental and weed plants showing symptoms resembling those caused by phytoplasmas were observed in Mahallat (central Iran). These plants were examined for phytoplasma infections by polymerase chain reaction (PCR) assays using universal phytoplasma primers directed to ribosomal DNA (rDNA). All affected plants gave positive results. The detected phytoplasmas were characterized and differentiated through restriction fragment length polymorphism (RFLP) and sequence analysis of PCR‐amplified rDNA. The phytoplasmas detected in diseased Asclepias curassavica and Celosia argentea were identified as members of clover proliferation phytoplasma group (16SrVI group) whereas those from the remaining plants examined proved to be members of aster yellow phytoplasma group (16SrI group) (‘Candidatus Phytoplasma asteris’). In particular, following digestion with AluI, HaeIII and HhaI endonucleases, the phytoplasma detected in Limonium sinuatum showed restriction profiles identical to subgroup 16SrI‐C; phytoplasmas from Gomphocarpus physocarpus, Tanatacetum partenium, Lactuca serriola, Tagetes patula and Coreopsis lanceolata had the same restriction profiles as subgroup 16SrI‐B whereas Catharanthus roseus‐ and Rudbeckia hirta‐infecting phytoplasmas showed restriction patterns of subgroup 16SrI‐A. This is the first report on the occurrence of phytoplasma diseases of ornamental plants in Iran.     

The fossil history of palms (Arecaceae) in Africa and new records from the Late Oligocene (28–27 Mya) of north-western Ethiopia

The African palm fossil record is limited but the data provide an outline of palm evolution from the Late Cretaceous through the Neogene. Pollen attributed to palms is reported from the Aptian (125–112 Mya), but the earliest unequivocal record in Africa is Campanian (83.5–70.6 Mya). Palms diversified 83.5–65.5 Mya and became widespread, although most records are from the west and north African coasts. Many taxa were shared between Africa and northern South America at that time, but a few were pantropical. Extirpations occurred throughout the Palaeogene, including a notable species turnover and decline at the Eocene–Oligocene boundary (33.9 Mya), a change that resulted in the elimination of nypoid palms from Africa. The Neogene plant macrofossil record is better sampled than the Palaeogene, although few palms are documented. Thus, the low diversity of African palms today is more likely the result of Palaeogene, rather than Neogene extinctions. Newly discovered palm fossils of leaves, petioles and flowers from the Late Oligocene (27–28 Mya) of north-western Ethiopia document the abundance and dominance of palms in some communities at that time. The fossils represent the earliest records of the extant genera Hyphaene (Coryphoideae) and Eremospatha (Calamoideae).  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 69–81.     

Pathogenicity of Fusarium oxysporum Isolates from Malaysia and F. oxysporuin f. sp. elaeidis from Africa to Seedlings of Oil Palms (Elaeis guineensis)

Pathogenicity tests with Fusarium oxysporum isolated form Malaysian oil palm were made with oil palms seedlings raised form Malaysian seed as well s with wilt-susceptible seedlings gown from African seed. Oil palm seedlings grown form Malaysian seed were also inoculated with African isolates of F. oxysporum f. sp. elaeidis and F. oxysporum var. redolens. The experiments were made under normal soil moisture conditions and under water stress. F. oxysporum f. sp. elaeidis isolates form Africa were pathogenic to oil palm seedlings from Malaysian seeds but the Malaysian F oxysporum isolates were non-pathogenic to plams grown from Malaysian seed or the wilt-susceptible palms from African seed. Seedlings from Malaysian seed proved to be highly susceptible to the vascular wilt disease caused by F. oxysporum f. sp. elaeidis as 75–90% of the palms were infected. The susceptibility of the palms from Malaysian seed varied with different African isolates tested. The Yaligimba isolate from Zaire which was found to be F. oxysporum var. redolens was the most virulent. Disease was more severe when oil palm seedlings were subjected to a period of water stress. The incidence of death in the seedlings under stress conditions was 45% as compared with only 15% for palms grown under normal conditions.     

Plant pathogenicity and transmission tests with Acholeplasma spp. isolated from coconut palms in Jamaica

Isolates of Acholeplasma spp. cultured from lethal yellowing-diseased coconut palms were characterised by polyacrylamide gel electrophoresis (PAGE) of cell proteins and by serological tests. Analysis of PAGE profiles placed 23 of the isolates in either of two related subgroups, (1A) or (IB), which show similarities to A. axanthum; 11 isolates were placed in group (2) which show similarities to A. oculi; and a single isolate formed a unique category (3). Serological relationships determined by fluorescent antibody and growth inhibition tests were in broad agreement with the PAGE classification. There was no evidence of transmission to plant hosts following injection of representative isolates into the cicadellids, Chlorotettix spp., Dalbulus maidis, Euscelidius variegatus or the cixid, Myndus crudus. Some isolates consistenty multiplied in E. variegatus following injection but were not acquired or transmitted during feeding through membranes. Antiserum to A. axanthum did not react with diseased or healthy palm tissues in enzyme-linked immunosorbent assay and the recovery of further acholeplasma isolates from palms affected by bud-rot disease demonstrated that these organisms were not specifically associated with lethal yellowing. The results suggested that these acholeplasmas are epiphytes or saprophytes on coconut palms.