Diseased Palms Research Articles

Characterizing the Palm Pathogenic Thielaviopsis Species from Florida.

Thielaviopsis paradoxa sensu lato is a soilborne fungal pathogen that causes Thielaviopsis trunk rot and heart rot in palms. The loss of structural integrity resulting from trunk rot can cause the palm trunk to collapse suddenly and poses a serious threat to life and property. Even though rudimentary knowledge about the Thielaviopsis infection process in palms is available, nothing is known about the T. paradoxa species complex in the US. The aim of this study was to characterize T. paradoxa s. lat. isolates collected from diseased palms grown in Florida. Multi-locus phylogeny using three genes, ITS, β-tubulin, and tef1-α, revealed that the isolates separate into two distinct clades with high bootstrap support. The majority of the isolates clustered with the species T. ethacetica, while two isolates formed a separate clade, distinct from T. musarum, and might represent an undescribed Thielaviopsis species. One representative isolate from each clade, when grown on three distinct media and at four different temperatures, showed differences in gross colony morphology, as well as growth rates. The T. ethacetica isolate TP5448 and the Thielaviopsis sp. isolate PLM300 grew better at opposite ends of the temperature spectrum tested in this study, i.e., 35 °C and 10 °C, respectively. In pathogenicity assays on whole plants, the T. ethacetica isolate proved to be more aggressive than Thielaviopsis sp. isolate PLM300, as it produced larger lesions when inoculated on wounded leaflets. An unequal distribution was observed for the mating-type locus of T. ethacetica, as 12 isolates carried the MAT1-1-1 allele, while the status for four isolates remained undefined. Variation in mycelial growth in response to different fungicides was also observed between the two clades. These results demonstrate the existence of two Thielaviopsis clades that can infect palms in Florida and underscore the need for targeted sampling to help uncover the diversity of Thielaviopsis species across palm-growing regions in the US.

Sample Collection for Ganoderma Butt Rot of Palms

Palms are an integral part of the urban landscape in Florida. Ganoderma butt rot of palms, a disease caused by the wood-decaying white-rot fungus Ganoderma zonatum, is one of the major biotic concerns for the landscape industry. The lethal disease is prevalent across palm-growing regions in the US, and all palm species are believed to be susceptible to this fungus. It may take six months to a year for the diseased palm to die once the initial symptoms appear. But with the availability of a disease diagnostic assay, this fungal pathogen can be detected using saw dust samples collected from declining palms, several months before symptoms appear. Collect good quality samples by following these steps and understanding the caveats associated with each step.

First report of a ‘Candidatus Phytoplasma australasia’‐related strain (16SrII‐D) associated with crown choking of areca palm in India

Areca palm (Areca catechu) is an economically important crop that is grown primarily in South Asia and South India, mainly in the states of Karnataka, Kerala and Maharashtra. With 0.73 million hectares cultivated and 1.2 million tonnes produced, India ranks first in world areca nut production. The state of Karnataka alone accounts 80% of annual production in India. During January 2021, crown choking symptoms (locally named “Hidimundige”), which resemble phytoplasma symptoms were observed on areca palm plantations. The highest disease incidence (50%) was recorded in Ajjarani, Sirsi Taluk and Uttara Kannda, followed by 30% in Haralakatta, Channagiri Taluk, Davanagere, Kelaginuru and Honnavara Taluk, in the district of Uttara Kannada (Karnataka state). The lowest disease incidence was 1% for the Dakashina Kannada and Tumkur districts in Karnataka.The most prominent symptom in infected palms was short, dark green leaves with a wavy leaf lamina. Leaflets failed to unfold properly leading to a bunchy top or witches’ broom appearance, and became crinkled and brittle. Reduced internodal length, drying of inflorescences and tapering of stem at the apex were also recorded. The roots became black, crinkled and brittle, and a pinkish or brownish discoloration was observed in the phloem. Affected plants failed to produce new leaves and existing leaves fell leading to a bare stem and death of the plant in quick succession (Figs. 1-3). About 80–100% of the plants died in affected areas. Seven leaf samples were collected from diseased palms growing in the Zonal Agricultural & Horticultural Research Station, Keladi Shivappa Nayaka University of Agricultural and Horticultural Sciences in Shivamogga, Karnataka (Latitude: 13° 55' 47.748“. Longitude: 75° 34' 5.1636”) during March 2022. Typical phytoplasma pleomorphic bodies lacking cell walls were seen in the sieve tube cells of leaf midrib sections from diseased areca palms, when examined by transmission electronic microscopy (Spurr, 1969) at the Sri Sai Histology Center, Hyderbad India (Fig. 4). The phytoplasma cell sizes ranged from 500 - 2000 nm. Seven leaf and three inflorescence samples from diseased palms and two leaf samples from asymptomatic palms were collected from the same location. Total DNA was extracted by the CTAB method and subjected to direct PCR using primers P1 (Deng & Hiruki, 1991) and P7 (Schneider et al., 1995) and nested PCR with R16F2n/R16R2 primers (Gundersen & Lee, 1996) that amplify the phytoplasma 16S rRNA gene. The expected direct (1.8 Kb) and nested (1.25 Kb) PCR products were obtained from all the diseased plant samples and positive reference controls but not from the symptomless plants. The R16F2n/R2 PCR products were cloned and sequenced directly at Biokart Pvt. Ltd., Karnataka, India, and the sequence deposited in GenBank (Accession No. ON606488). The R16F2n/R2 sequence was subjected to BLAST analysis and showed the highest nucleotide identity (99.92%) with 16SrII phytoplasma isolates, ‘Candidatus Phytoplasma aurantifolia’ (MT555412, MT555411) identified in Croton bonplandianus in Maharashtra, India. Virtual RFLP analysis of the R16F2n/R2 sequence with iPhyClassifier yielded an RFLP pattern identical to that of the 16Sr group II, subgroup D (Y10097) with a similarity coefficient of 1.00. Phylogenetic analysis (MEGA 7.0.18) using the neighbour-joining algorithm with selected phytoplasma reference strains confirmed that the areca palm phytoplasma clustered within the clade of phytoplasma strains of the 16SrII group (Fig. 5). In India, the cultivation of areca nut is mostly limited to the states of Assam, Karnataka and Kerala, and palms in these areas are affected by a yellowing disease named yellow leaf disease (YLD). YLD is one of the most important diseases of this palm species (Nambiar, 1949) and it is associated with the 16SrXI phytoplasma group, ‘Ca. P. oryzae’. (Chaithra et al., 2014). ‘Ca. P. aurantifolia’ is known to infect several plant species in India (Rao et al., 2017). However, this is the first report of a ‘Ca. P. aurantifolia’- related strain causing crown choking of Areca catechu in India. The impact of crown choking on areca nut yield, the geographic distribution of the disease and its epidemiological implication in India are currently under investigation.

An Integrated Disease Management of Oil Palms Affected by Bud Rot Results in Shorter Recovery Times

Bud rot is a limiting disease that affects most oil palm crops destroying thousands of hectares in Latin America. Bud rot (BR) is caused by the oomycete Phytophthora palmivora (Butler). Integrated disease management (IDM) technology has been used to control the disease, which slows down the progress of the disease, allowing palm recovery. However, the effect of this technology on the recovery speed of treated palms is not well known. We studied the time taken for palm recovery from BR under the integrated management approach. The study was carried out on 21 oil palm commercial cultivars dura × pisifera (D × P) and O × G hybrids affected by BR in the Colombian oil palm Central Zone. The analysis included different recovery times (RT), the severity degree, time of the year (wet or dry season), number of reinfections, and cultivar. The RT of bud rot-affected palms ranges from 103 to 315 days, with an average of 202.8 days when an IDM is used. RT was lower than that reported in the diseased palms without IDM (540 days). According to the severity degree, the RT lasted 202 days for severity degree 1, 198 days for severity degree 2, and 222 with severity degree 3 and 4. In comparison, there was no significant difference between dry and rainy seasons in RT. Differences between cultivars were found; however, under IDM, all cultivars showed low RT. The IDM has a positive impact in reducing the RT to BR. Low RT has indirect effects minimizing potential yield losses, improving the number of successfully recovered palms, and reducing the risk of disease dissemination.

Diseased palm removals as a strategy for the successful managementof Weligama coconut leaf wilt phytoplasma disease of coconut in SriLanka

Weligama coconut leaf wilt disease is a seriously debilitating disease affecting coconut in the Southern province of Sri Lanka since 2006. It has been declared as a quarantine disease and the Coconut Research Institute of Sri Lanka identified removal of the diseased palms as the strategy to stop the further spread of the disease to the unaffected areas. Therefore, the diseased palms identification and removal program is in progress since 2008 in this area. Under this program 339,271 diseased palms have been removed. Because of this management strategy the disease is to date confined only to the Galle, Matara and Hambanthota districts in the Southern part of the country. After minimizing the disease pressure of the area, re-planting coconut with resistant varieties was identified as the viable long-term solution to combat the disease.

Generating the Baseline in the Early Detection of Bud Rot and Red Ring Disease in Oil Palms by Geospatial Technologies

Oil palm cultivation in Ecuador is important for the agricultural sector. As a result of it, the country generates sources of employment in some of the most vulnerable zones; it contributes 0.89% of the gross domestic product and 4.35% of the agricultural gross domestic product. In 2017, a value of USD $252 million was generated by exports, and palm contributed 4.53% of the agricultural gross domestic product (GDP). It is estimated that 125,000 hectares of palm were lost in the Republic of Ecuador due to Red Ring Disease (RRD) and specifically Bud Rot (BR). The current study aimed to generate an early detection of BR and RRD in oil palm. Image acquisition has been performed using Remotely Piloted Aircraft System (RPAS) with Red, Green, and Blue (RGB) cannons, and multispectral cameras, in study areas with and without the presence of the given disease. Hereby, we proposed two phases. In phase A, a drone flight has been conducted for processing and georeferencing. This allowed to obtain an orthomosaic that serves as input for obtaining several vegetation indices of the healthy crop. The data and products obtained from this phase served as a baseline to perform comparisons with plantations affected by BR and RRD and to differentiate the palm varieties that are used by palm growers. In phase B, the same process has been applied three times with an interval of 15 days in an affected plot, in order to identify the symptoms and the progress of them. A validation for the diseases detection has been performed in the field, by taking Global Positioning System (GPS) points of the palms that presented symptoms of BR and RRD, through direct observation by field experts. The inputs obtained in each monitoring allowed to analyze the spatial behavior of the diseases. The values of the vegetation indices obtained from Phase A and B aimed to establish the differences between healthy and diseased palms, with the purpose of generating the baseline of early responses of BR and RRD conditions. However, the best vegetation index to detect the BR was the Visible Atmospherically Resistant Index (VARI).

Chlorophyll a fluorescence and leaf temperature are early indicators of oil palm diseases

Bud rot (BR) caused by Phytophthora palmivora and lethal wilt (LW) whose causal agent is unknown, are two diseases currently posing a threat to the oil palm ( Elaeis guineensis . Jacq) industry. BR, first reported in 1964, has destroyed more than 85,000 ha. LW, first reported in 1994 in the Llanos Orientales in Colombia, has destroyed more than 5,000 ha. Chlorophyll a fluorescence is useful as a provider of information about the efficiency of the photosynthetic process when plants are subjected to biotic or abiotic stresses. Oil palms affected by BR and LW showed anomalies in the photosynthetic system, manifested by reductions in Fv / F M and ΦPSII. Changes in ΦPSII, variable fluorescence yield ( Fv ) and maximum fluorescence in light-adapted leaves ( F M ’ ) were observed from the start of BR infection. The most sensitive and early indicators of LW disease were leaf temperature and basal fluorescence ( F 0 ). Fv/F 0 significantly changed in diseased palms, indicating problems with movement of electrons through the electron transport chain. Leaf temperature changed in response to both diseases, but variation was greater in LW. We concluded that damage to the photochemical system caused by the diseases affected the processes by which the plant captures and transports energy, causing a physiological imbalance in the plant reflected in the observed variations in chlorophyll a fluorescence and leaf temperature. The two parameters began to change early in the onset of BR and before visual symptoms appeared in LW, which is very important to the management of both diseases, the foundation of which is early detection.

Field Spectroradiometry for African Oil Palm Plantations in the Pacific of Costa Rica

This study allowed the leaf-scale spectral characterization of African oil palm by conducting field work with a portable spectroradio meter in plantations of the Central and South Pacific of Costa Rica. Spectral signatures of healthy, diseased and nutrient-deficient oil palms were collected. A geodatabase was designed and implemented for geographical, spectral and phytosanitary records. Determination of spectral signatures allows developing spectral libraries of different types of vegetation, soils and water. It also improves the classification of satellite images for thematic cartography and provides the calculation of multiple indices, among others. Healthy vegetation presents low reflectivity in the visible, although there is a peak in the green wavelength due to the presence of chlorophyll. The spectral behavior of diseased vegetation shows a reflectivity curve with a decrease in the infrared and an increase in the red and blue wavelengths. Reflectivity also depends on the water content of the plant.

An analysis of spectral variability in hyperspectral imagery: a case study of stressed oil palm detection in Colombia

ABSTRACTHyperspectral images have acquired an increasing interest in the scientific and civil community to detect or classify materials by their spectral signature in remote sensing applications. However, spectral signatures can vary because of lighting or atmospheric conditions. This phenomenon is known as spectral variability, and ignoring this variability is an important source of error in the analysis of hyperspectral images. Therefore, this work focuses on analysing different causes and effects of the spectral variability in hyperspectral images, by studying the latest advances in this area, including approaches that do not address the phenomenon and methods that address spectral variability. Experiments are executed with five different approaches to compare their accuracy in the estimation of abundances in synthetic data generated with spectral variability. Specifically, a case study is developed on hyperspectral data of oil palm crops in Colombia, which exhibit high spectral variability. The results of identification of stressed oil palms are compared by mapping the abundances of three classes (diseased oil palm, healthy oil palm, and background), evaluating the performance of the different approaches in terms of the root mean squared error (RMSE), reconstruction error (RE), and spectral angle mapping (SAM). Results show that the coordinate descent algorithm-mismodelling effects (CDA-ME) present the best performance, outperforming in up to 70% the other approaches with and without spectral variability since it can jointly model changes of illumination, effects of variability and outlier values present in the hyperspectral images.

Rapid Inoculation Technique and Biological Control of Leaf Spot Disease in Oil Palm

Oil palm (Elaeis guineensis) is one of the most efficient oil-producing crops in the world. However, fungal diseases such as basal stem rot (BSR) caused by Ganoderma sp. causes significant loss to the yield of adult palms. Apart from BSR, leaf spot disease caused by Curvularia sp. also causes significant loss during nursery stages. In this study, Curvularia sp. was isolated from a diseased palm seedling and a rapid and reproducible artificial inoculation method was developed. The technique has bioassay to determine the level of success of the control of leaf spot disease in a glasshouse setting. A natural, organic cyclic peptide fungicide and living cells of a bacterial strain Paraburkholderia sp. CP01 were tested for their efficacy to control leaf spot in oil palm seedlings. The severity of leaf spot disease in oil palm seedlings treated by organic cyclic peptide fungicide and CP01 was significantly lower than untreated control, indicating potential biological control agents. The results presented here provide technical reference and novel approach to controlling leaf spot disease of oil palm.

Molecular identification and pathogenicity of Phytophthora nicotianae-caused bud rot disease of Washingtonia palms in Saudi Arabia and use of Lysobacter enzymogenes as a bioagent in an in vitro study

Severe terminal bud rot disease symptoms of Washingtonia, Washingtonia robusta, palms were observed in the 5-year-old trees in a farm located at the north of Al Shehia governorate, Qassim region, Saudi Arabia. The fungus found associated with the diseased palm buds was isolated in the laboratory, and pathogenicity tests were conducted on healthy 1-year-old Washingtonia palms, at an experimental station, Agriculture and Veterinary Medicine. Pathogenicity tests showed that a single fungus caused typical symptoms of bud rot on the inoculated trees. Petiole bases and terminal buds were rotted after 5–6 weeks of inoculation. The pathogen was identified through microscopy and characterized molecularly, using internal transcribed spacer (ITS) regions of ribosomal DNA, as a fungal-like organism Phytophthora nicotianae (synonym = P. parasitica). Experiments were conducted on the biological control of the pathogen in the laboratory, and a promising RN13 isolate of Lysobacter enzymogenes was selected for further study. This study seems to be the first report of bud rot disease of Washingtonian palms caused by P. nicotianae in Saudi Arabia. Great attention should be given to this disease because it is soil borne and may be transmitted to the date palm crop.

First Record of the Invasive Neotropical Ambrosia Beetle Euplatypus Parallelus (Fabricius, 1801) (Coleoptera: Curculionidae: Platypodinae) Infesting Arecanut in Karnataka, India

An infestation of the ambrosia beetle, Euplatypus parallelus (F.) (Coleoptera: Curculionidae: Platypodinae) on arecanut, Areca catechu L., is reported from the state of Karnataka in southwestern India for the first time. The visible symptoms on healthy and younger palms include oozing of a yellowish brown resinous exudation from infested stems. Small, pinheadsize holes were visible after removal of the resinous exudation. Symptoms on older, stressed, and diseased palms appear as extrusion of sawdust frass in the form of loose, cylindrical strings. Fronds of infested palms lose vigor and turn yellow. The size of the larval galleries varied 1.40–1.46 mm in diameter. Large numbers of larvae, pupae, and adults were found in the galleries of affected palms. Adult beetles are slender, 4.0–4.2mmlong, and brownish with yellowish hairs. Male and female specimens were distinguished based on the elytral declivity. The taxonomic identity of the species was confirmed by amplification of 649 base pairs of the mitochondrial cytochrome oxidase I gene. In a climate change scenario, this beetle may become a serious threat to arecanut production in India and elsewhere.

First report of a ‘Candidatus Phytoplasma palmae’-related subgroup 16SrIV-D phytoplasma on Trachycarpus fortunei

Chinese windmill palms (Trachycarpus fortunei) exhibiting canopy decline symptoms suspected of being associated with a phytoplasma were observed in a residential landscape in Baton Rouge, Louisiana, USA. Internal stem tissue from diseased palms was tested for the presence of date palm lethal decline and lethal yellowing-related phytoplasmas. A ‘Candidatus Phytoplasma palmae’-related subgroup 16SrIV-D phytoplasma was detected by restriction fragment length polymorphism analysis and confirmed by sequencing. The subgroup 16SrIV-D phytoplasmas have previously been reported on buccaneer palm, cabbage palm, Canary Island date palm, edible date palm, green thatch palm, pigmy date palm, queen palm, Rio Grande palmetto, and silver date palm. To the best of our knowledge, this is the first report of a ‘Ca. P. palmae’ -related subgroup 16SrIV-D phytoplasma on T. fortunei.

Comparative transcriptome profiling of healthy and diseased Chowghat Green Dwarf coconut palms from root (wilt) disease hot spots

Understanding the molecular basis of host-pathogen interactions is imperative for devising disease management strategies. The root (wilt) disease is the foremost debilitating disease threatening coconut production in India. To explore the molecular mechanisms involved in compatible and incompatible interactions, global transcriptome profiling of leaves of healthy and diseased Chowghat Green Dwarf (CGD) palms was conducted. RNA-Seq analysis generated more than 190 million 100 bp reads from both healthy and diseased samples. Assembled transcriptome yielded 59,282 transcripts with a median length of 987 bp. BLASTX annotation of transcriptome resulted in 39,665 transcripts getting annotated from Uniprot and date palm proteome database. Differential gene expression profiling analysis revealed 2718 transcripts to be up- or down- regulated in the diseased palms in comparison to healthy control at a fold change of 2 and above with a p value <=0.05. The differentially expressed transcripts could be categorized into pathways which included cell wall biogenesis, primary and secondary metabolism, plant-pathogen interaction, cellular transport, hormone biosynthesis and signaling. Validation by quantitative real time PCR (RT-qPCR) of a set of arbitrarily selected genes, both up-regulated and down-regulated, established a comparable pattern as observed by RNA-Seq analysis. Overall, the resources generated in this study provide an in-depth analysis and new insights into the interaction of coconut palms with the root (wilt) disease pathogen.

First report of a ‘Candidatus Phytoplasma aurantifolia‘‐related phytoplasma strain associated with yellowing symptoms on pineapple palm in Iran

Pineapple palm, Phoenix canariensis, is one of the most widely grown and appreciated ornamental palms, including in the south of Iran. During the last three years, symptoms resembling nutrient deficiency were observed on pineapple palms in urban landscapes in Ahvaz in southwestern Iran. The symptoms included leaf yellowing in the lower fronds which began from the leaf tips and extended towards the blade and the rachis (Figs. 1, 2, 3). During January 2016, P. canariensis palms were surveyed for phytoplasma. Leaf samples from three diseased and one symptomless palm were collected. The midribs were freeze-dried and then powdered in liquid nitrogen. Total DNA was extracted using a CTAB-based method (Maixner et al., 3). Total DNA was analysed by nested PCR assay using generic primers P1/P7-R16F2n/R16R2 (Deng & Hiruki, 1; Gundersen & Lee, 2). Amplicons of the expected size (c. 1.2 kb) were obtained from all diseased palms, and were purified (GF-1 AmbiClean Kit, Malaysia) and directly sequenced. The partial consensus 16S rDNA sequence was deposited in GenBank (Accession No. KX088466) and compared to those of reference phytoplasmas by BLAST analysis. The consensus 16S rDNA sequence showed 99% sequence identity to members of group 16SrII ‘Candidatus Phytoplasma aurantifolia’. A phylogenetic tree (Fig. 4) based on the 16S rDNA sequences of P. canariensis phytoplasma and those of reference phytoplasmas was constructed using the maximum likelihood algorithm under the TN93+G+I model of the MEGA 6 software (Tamura et al. 4). The P. canariensis phytoplasma (Ahvaz-5 isolate) clustered within the 16SrII phytoplasma group. Restriction mapping of the partial 16SrRNA sequence (1161bp) with typical endonucleases AluI, BamHI, BfaI, BstUI, DraI, EcoRI, HaeIII, HhaI, HinfI, HpaI, HpaII, KpnI, Sau3AI, MseI, RsaI, SspI and TaqI in a virtual digest using Restriction-Mapper V.3 online software (http://www.restrictionmapper.org) showed that the virtual RFLP pattern of the P. canariensis phytoplasma was identical (similarity coefficient 1.00) to the reference pattern of subgroup 16SrII-D (Y10097). Both, the virtual RFLP and phylogenetic analyses confirmed that the P. canariensis phytoplasma is a member of the 16Sr II group, subgroup D. Phoenix canariensis is affected by the Texas phoenix palm decline phytoplasma, a member of the 16SrIV group, in Florida and Texas, USA. To our knowledge, this is the first report of a phytoplasma disease on palm in Iran. The P. canariensis phytoplasma (Ahvaz-5 isolate) is affecting approximately 20% of the pineapple palms in Ahvaz. The identification of this phytoplasma will contribute to improving the future management of the disease.

Detection of Root (Wilt) Disease of Coconut (Cocos nucifera L.) based on polyacrylamide gel electrophoresis

&lt;div&gt;&lt;p&gt;&lt;em&gt;Root (wilt) disease (RWD), caused by phytoplasma, is a major problem causing decreased coconut productivity in southern districts of Kerala and its bordering districts of Tamil Nadu in India. The disease is non-curable but its incidence can be reduced by propagating seedlings from nuts of disease free palms. The disease free palms are selected by ELISA test which uses antiserum obtained from rabbits against purified phytoplasma extract containing 29, 28 and 18.5 K Da proteins. With an objective of developing a simpler and easier biochemical test than ELISA for RWD detection in coconut , direct SDS PAGE profiles of soluble proteins from crude leaf extracts of healthy and diseased palms of West Coast Tall (susceptible) , Chowghat Green Dwarf and Malayan Green Dwarf (high degree resistant) cultivars were evaluated&lt;/em&gt; &lt;em&gt;for differences in intensities of protein bands with molecular masses corresponding closest to the purified phytoplasma extract proteins. It was found that the 31.2, 37.3, 16.9 and 13.8 KDa bands in WCT cultivar, 31 and 40.6 KDa in CGD cultivar and 29.9 and 37.1 KDa bands in the MGD cultivar showed consistent differences in intensities and/or presence or absence of certain bands between healthy and diseased palms. Correlations and path analysis relationship between intensity of different protein bands and ELISA value also showed significant association of one or two of these marker bands with ELISA values in each cultivar. The&lt;/em&gt; &lt;em&gt;SDS PAGE profiles of crude leaf extracts could be used to effectively distinguish healthy and diseased RWD palms in these three cultivars.&lt;/em&gt;&lt;strong&gt;&lt;/strong&gt;&lt;/p&gt;&lt;/div&gt;

Advances in the Interpretation of Tomographic Images as an Early Detection Method of Oil Palm Affected by Basal Stem Rot in Colombia.

Basal stem rot, one of the most important diseases of oil palm in Southeast Asia, has also been identified in Colombia. The increase in disease incidence in the last decade has attracted the attention of producers and researchers. In the search for a procedure that allows for the early identification of diseased palm, Cenipalma evaluated the use of electrical impedance tomography to identify the different stages of development of basal stem rot. The tomograms were compared with transversal sections of healthy and diseased oil palm trees. Following Cenipalma's preliminary studies on early diagnosis of basal stem rot with tomography, the present study improved upon the technique by analyzing the tomograms of 209 diseased palm trees (confirmed by symptomatology), 346 asymptomatic palm trees, and 132 healthy palm trees. The minimum and maximum electric impedance values as well as the ratio between these values was recorded. The range of 1 to 95 Ω was used to represent the internal damage. The ratios averaged 5.1 for diseased, 1.9 for asymptomatic, and 1.5 for healthy palm trees. With the range and the ratio criteria established, it was possible to identify the disease in 100% of asymptomatic sampled palm trees. This study demonstrated that electrical impedance tomography is a powerful tool for early detection of basal stem rot, which can be used to establish an early disease management program.

Preliminary Evaluation of Electrical Resistance Tomography for Imaging Palm Trunks

In a preliminary study, electrical resistance tomography (ERT) was used to obtain trunk images of Syagrus romanzoffiana, a common ornamental palm grown in southern Florida, U.S. Seven palms, four healthy and three diseased, were evaluated in the middle of the dry season, with four located in an irrigated site and three in a non-irrigated site. Two healthy and three diseased palms were felled and cross sections obtained to examine their internal structure and compare to the tomograms obtained. ERT was effective in illustrating the relative electrical resistance value of healthy palms, as the tomograms obtained for palms situated in the irrigated site (low electrical resistivity) were distinctly different from the tomograms of palms situated in the non-irrigated site (high electrical resistivity). ERT was also effective in visualizing internal palm trunk areas affected by the fungal pathogens Ganoderma zonatum, a wood decay pathogen, and Fusarium oxysporum f. sp. palmarum, a vascular wilt pathogen, as these areas had a low electrical resistivity.

Interactions Between the Bud Rot Disease of Oil Palm and Rhynchophorus palmarum (Coleoptera: Curculionidae).

Rhynchophorus palmarum (L.) causes great losses to the oil palm plantations, and therefore, the spatial and temporal distribution of this insect should be studied, to manage its populations. Insect sampling was done for 2 yr in an oil palm plantation from Colombia. In total, 60 pheromone traps were used in healthy palm trees and infected ones with the Bud Rot disease. On the other hand, developmental stages of this insect were quantified on healthy and diseased palms for two consecutive years. Number of adult R. palmarum per sampling was higher in the plantation with diseased palm trees, 3.85 and 74.7 insects per trap, than in those with healthy ones, 1.91 and 9.48 insects per trap, in the first and second years, respectively. After the integration of pheromone traps, there was a significant increase in the infestation level at all stages of development of the insect. For the first time, the presence of R. palmarum attracted to diseased palms is reported. The association between R. palmarum and the Bud Rot disease is a cause of death and great loss to the oil palm plantations.

Application of light microscopic staining techniques for the detection of phytoplasmas in yellow leaf disease affected arecanut palms in India

Yellow Leaf Disease (YLD) is one of the most drastic diseases affecting the areca nut palms of Kerala and Karnataka causing extensive crop loss. The disease is associated with phytoplasma presence. A classic diagnostic technique was the observation of symptoms on the leaves however microscopic studies can be used for pathogen visualization along with molecular methods. Although the direct observation of phytoplasmas requires the magnification achieved only by electron microscopy, light and fluorescence microscopy can also be used to detect the presence of phytoplasmas in diseased palm tisues. Dienes’ stain and DAPI fluorescent microscopic method developed for confirming the presence of phytoplasma in hand cut or freezing microtome sections of infected tissues were employed. In the present study, YLD affected plants gave positive results for phytoplasma specific staining. Fluorescent particles of the DAPI-stained phytoplasma were limited to sieve tube elements. Phloem of healthy root sections remained unstained with Dienes’ stain, but phloem of the infected root sections contained many dark blue DAPI stained areas. The results from the present study indicated that these methods can be used as preliminary steps in phytoplasma presence detection, and are found to be very effective in highly infected plants. The microscopic observation of phytoplasma cells could be used as a confirmative step for subsequent application of molecular diagnostic techniques.