Coconut Seedlings Research Articles

First Report of <i>Curvularia pseudobrachyspora</i> Causing Leaf Spots Disease on Coconut (<i>Cocos nucifera</i> L.) Seedlings in Ghana

Coconut (Cocos nucifera L.) is an important oilseed and a multipurpose perennial plantation crop. It is mostly grown in humid and coastal areas of Ghana. In June 2019, leaf spot disease was observed on coconut seedlings in 10 coconut growing Districts in Ghana. The Initial symptoms appeared as elliptical, brown-dark-red lesions, 4 - 6 mm on affected leaves. Lesions reached 2.0 cm and gradually developed into spindly, dark brown spots with a light tan centre. A study including survey and laboratory work was carried out to assess disease prevalence and to identify the causal agent of the disease on coconut seedlings, in order to formulate effective management strategies against it. A total of 250 symptomatic leaves were picked from ten selected Districts for laboratory analysis. Additionally, the ribosomal internal transcribed spacer (ITS) region and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) of the isolated pathogen were amplified using ITS1 and ITS4, gpd1 and gpd2 primers respectively. The disease incidence peaked at 95%. Fungal colonies on PDA grew to 50 - 70 mm in diameter in one week at a temperature of 28°C ± 1°C with an even to undulating, immersed striated, mycelium; aerial mycelium being dark velvety green and sometime woolly-cottony. Acervuli formed on the aerial mycelium and contained black powderish conidial masses. Hyphae characteristics were similar to that of Curvularia pseudobrachyspora. Pathogenicity tests were done following Koch’s postulate. For molecular confirmation, the combined ITS (MT075719) and GAPDH (MT075720) sequences were compared with published sequences of 52 Curvularia isolates and eight Bipolaris isolates using phylogenetic analysis. This is the first report of C. pseudobrachyspora as a causal agent of leaf spot on coconut seedlings in Ghana and possibly Africa but the pathogen has been reported on other crops in China, Florida and India.

Development of IPM module for rhinoceros beetle (Oryctes rhinoceros L.) in juvenile coconut garden

Coconut (Cocos nucifera) is an important crucial plantation crop and prone to many pests and diseases. Rhinoceros beetle (Oryctes rhinoceros L.) is an important pest that causes damage and reduce the yield. During 2018, Gaja cyclone affected the coconut plantations in delta regions of Thanjavur, Thiruvarur and Nagapattinm Districts. Rhinoceros beetle was found to inflict severe damage in replanted young coconut seedlings. The present study was carried out to mitigate the damage due to rhinoceros beetle in coconut gardens. Shoot damage of 14.07, 11.36, and 18.17 per cent was recorded in Module - I recommended practice, Module - II IPM and module - III farmers’ practice respectively. The maximum shoot damage reduction of 37.48 per cent was observed over farmers’ practice recorded in Module - II IPM followed by recommended practice (22.56%). Module - II IPM was found to be effective against rhinoceros beetles than recommended practice and farmers’ practice.

Beneficial Effect of Biochar on Irrigated Dwarf-Green Coconut Tree

The coconut tree is considered one of the greatest consumers of irrigation water, ranging from 100 to 240 L day−1. The objective of the present study was to evaluate the effect of biochar application on decreased irrigation water needs in a 2-year irrigated dwarf coconut palm orchard field experiment. Biochar was characterized chemically and by electron microscope images. Biochar morphology presented several micropores indicating water retention potential. Amounts of biochar were tested (0, 5, 10, 20, 40 g of biochar per kg of soil), representing 0.0; 0.5; 1.0; 2.0; and 4.0 kg per plant. Micro sprinkler irrigation started following the planting of the 90-day old hybrid dwarf coconut seedlings. The impacts of the application of the biochar on the chemical attributes of the soil, biometry of the coconut plants, water storage in the 0–0.3 m soil layer, and the volume of irrigation water required by treatment were evaluated. After two years (2017 and 2018), the application of the biochar resulted in no statistically significant differences in the chemical attributes of the soil and biometric variables of plants between different treatments. The volume of annual irrigation water per plant versus biochar quantity demonstrated a decreasing effect, due to the increase of soil water storage. The dose of 40 g of biochar per kg of soil presented the highest two-year average soil water retention (0–0.3 m layer) among treatments (34, 36, 34, 38, and 45 mm, respectively), resulting in lower 2-year irrigation water demand (28, 36, 29, 28 and 20 L plant−1 day−1, respectively).

Phosphogypsum Organic, a Byproduct from Rare-Earth Metals Processing, Improves Plant and Soil

Phosphogypsum organic (PG organic) is a soil conditioner, derived from residues, water leach purification (WLP) and neutralisation underflow (NUF) from rare-earth metals processing in combination with composted organic material. There was no report available with regards to the effectiveness of this byproduct for crops improvement in a sandy soil texture. Therefore, a field trial involving a multi-crop was conducted by the addition of PG organic on a sandy texture soil for 23-month period. Guinea grass or guinea grass intercropping with teak wood trees, corn and kenaf showed an improvement in cumulative fresh yield in plot treated with PG organic either with a half- or full-fertilizer recommended rate for the respective crop as compared to control. The same trend was also observed in teak wood trees in hole planting systems and pandan coconut seedlings in the polybags. Application of PG organic in each season showed a consistently higher cumulative fresh yield or yield for certain crop types due to soil ability to maintain the soil pH buffering capacity (pH 5.8–6.0). Therefore, the application of PG organic as soil conditioner promotes plant growth and development due to the improvement of soil condition by creating suitable ecosystem for nutrients absorption by roots.

The importance of coconut seedling production in guyana

The demand for coconut water and coconut oil is increasing thus there is interest in expanding coconut cultivation. Coconut is primarily planted on approximately 28,500 acres by more than 1,400 farmers along the Guyana coastline with the Atlantic Ocean and in the Pomeroon Riverain area. Tall types (e.g. Jamaica Tall) are planted for oil while Dwarf types (e.g. Malaysian Dwarf Green, Suriname Brown) are planted primarily for water. At least 50% of the Tall type population is more than 50 years old and needs to be replanted to increase productivity. Farmers traditionally collect seedlings growing from dropped nuts at the base of trees without attention to prolificacy. Since a coconut tree productive life is more than 50 years, the economic impact of this practice can be significant. Via training programs, CARDI is encouraging the structured production of coconut seedlings to increase yields. This project aims to enhance the supply of quality seedlings using local seed nuts. Mother palms that display prolific bearing habits, resistance to pest and diseases plus vigorous growth habit were geotagged and recorded in a database. Seed nuts were purchased from farmers who own these trees and subsequently distributed (in batches of 400) to ten selected (age, gender, location) lead farmers to establish coconut seedling nurseries. Each lead farmer was assisted by 10 second ring farmers in the establishment of their nurseries under CARDI supervision. Results to date show that weed control and irrigation were important nursery activities. Some nurseries needed to be fenced to counter damage by animals (cows, sheep, goats). Average germination of seed nuts was approximately 50%. Available seedlings are being distributed to second ring farmers and lead farmers. CARDI will continue the national survey to identify outstanding mother palms. Measures to increase average germination must also be implemented. Local coconut seedling nurseries should therefore be encouraged as their “success” will alleviate the pressure to import seed nuts thus avoiding the attendant risk of introducing exotic diseases (e.g. lethal yellowing disease) into Guyana. Further, given that a coconut palm will live 50 to 70 years, the importance of carefully selecting premium quality coconut seedlings as a bedrock to develop and grow the industry cannot be over emphasized.

Bacillus cereus Improves Performance of Brazilian Green Dwarf Coconut Palms Seedlings With Reduced Chemical Fertilization.

Coconut production in the Amazon requires the knowledge and development of sustainable technologies to alleviate the detrimental effects of inorganic chemical fertilizers and intensive farming practices. In this study, we investigated the effects of plant growth-promoting rhizobacteria (PGPR) isolated from coconut seedlings on nutrient use efficiency (NUE) and physiological mechanisms related to biomass accumulation of seedlings grown with reduced inorganic fertilizer levels. Of the 96 PGPR isolates tested on rice plants, the isolate Bacillus cereus (UFRABC40) was selected, as it resulted in the most significant gain in growth variables. In a commercial coconut tree nursery, we subjected seedlings to two treatments, both with seven replications: control 100% NPK chemical fertilizer (CF) and B. cereus + 50% NPK CF. The results indicated that the inoculation increased phytohormone levels [190% indole acetic acid (IAA), 31% gibberellic acid GA3, and 17% gibberellic acid GA4] and leaf gas exchange [48% by assimilation of CO2 (A), 35% stomatal conductance to water vapor (gs), 33% transpiration, and 57% instantaneous carboxylation efficiency] in leaves. Furthermore, growth parameters (shoot, root, and total dry weight, height, and diameter) and macro- and micronutrient levels (95% N, 44% P, 92% K, 103 Ca, 46% Fe, 84% B) were improved. Our results show the potential ability of strain Bacillus cereus UFRABC40 to promote the growth performance of coconut seedlings under decreased application of inorganic fertilizers. The application of microbial-based products in coconut seedling production systems improves plants’ physiological performance and the efficiency of nutrient use.

The importance of coconut seedling production in Guyana

The demand for coconut water and coconut oil is increasing thus there is interest in expanding coconut cultivation. Coconut is primarily planted on approximately 28,500 acres by more than 1,400 farmers along the Guyana coastline with the Atlantic Ocean and in the Pomeroon Riverain area. Tall types (e.g. Jamaica Tall) are planted for oil while Dwarf types (e.g. Malaysian Dwarf Green, Suriname Brown) are planted primarily for water. At least 50% of the Tall type population is more than 50 years old and needs to be replanted to increase productivity. Farmers traditionally collect seedlings growing from dropped nuts at the base of trees without attention to prolificacy. Since a coconut tree productive life is more than 50 years, the economic impact of this practice can be significant. Via training programs, CARDI is encouraging the structured production of coconut seedlings to increase yields. This project aims to enhance the supply of quality seedlings using local seed nuts. Mother palms that display prolific bearing habits, resistance to pest and diseases plus vigorous growth habit were geotagged and recorded in a database. Seed nuts were purchased from farmers who own these trees and subsequently distributed (in batches of 400) to ten selected (age, gender, location) lead farmers to establish coconut seedling nurseries. Each lead farmer was assisted by 10 second ring farmers in the establishment of their nurseries under CARDI supervision. Results to date show that weed control and irrigation were important nursery activities. Some nurseries needed to be fenced to counter damage by animals (cows, sheep, goats). Average germination of seed nuts was approximately 50%. Available seedlings are being distributed to second ring farmers and lead farmers. CARDI will continue the national survey to identify outstanding mother palms. Measures to increase average germination must also be implemented. Local coconut seedling nurseries should therefore be encouraged as their “success” will alleviate the pressure to import seed nuts thus avoiding the attendant risk of introducing exotic diseases (e.g. lethal yellowing disease) into Guyana. Further, given that a coconut palm will live 50 to 70 years, the importance of carefully selecting premium quality coconut seedlings as a bedrock to develop and grow the industry cannot be over emphasized.

Development of the first axillary in vitro shoot multiplication protocol for coconut palms

The coconut palm or “tree of life” is one of nature’s most useful plants and the demand for its fruit is increasing. However, coconut production is threatened by ageing plantations, pests and diseases. Currently, the palm is exclusively propagated via seeds, limiting the amount of planting material. A novel micropropagation method is presented, based on axillary shoot formation. Apical meristems of in vitro coconut seedlings are cultured onto Y3 medium containing 1 µM TDZ. This induces the apical meristem to proliferate through axillary shoots in ~ 27% of the initiated explants. These axillary shoots are seen as white clumps of proliferating tissue and can be multiplied at a large scale or regenerated into rooted in vitro plantlets. This innovative micropropagation method will enable the production of disease-free, high quality in vitro plantlets, which will solve the worldwide scarcity of coconut planting material.

Effect of sea water substitution on growth, physiological and biochemical processes of coconut (Cocos nucifera L.) seedlings—A hydroponic study

Coconut is grown along the coasts and islands that are vulnerable to climate change-induced sea level rise. Though coconut is considered moderately salt tolerant, our understanding on the growth and physiological response to sea water, either inundation or subsurface water contamination, is very limited. This understanding will enable to effectively manage coconut in coastal systems under future climatic scenarios. In this study, ten month old hydroponically grown coconut seedlings were subjected to 0, 10, 25, 50, 75 and 100 % of sea water substitution (SWS), equivalent to 2.17, 8.32, 16.32, 30.03, 42.14 and 53.69 dS m−1 EC, respectively. Substituting Hoagland solution in hydroponic system by sea water of increasing concentration (>50 % SWS) significantly changed physiological processes; Fv/Fm decreased and rs increased as early as 7 and 18 days after treatment imposition (DAT), respectively which led to significant decline in leaf area and root length expansion as early as 24 DAT. At 25 % SWS, root system (root length and root biomass) was stable but the aerial part biomass was declined by 47 %. On the other hand plant height, leaf area, collar girth and biomass accumulation of seedlings under 10 % SWS (8.32 EC) was on par with the control plants suggesting coconut seedlings could tolerate 10 % SWS. Though, PN declined by 19 % and 43 % at 10 % and 25 % SWS, respectively and a similar decline in gs without a concomitant change in leaf water potential suggested that root-generated signals regulated the stomatal movement in coconut under salinity. Still the biomass accumulation at 10 % SWS was not affected by decline in PN. Under increasing sea water treatments, most of the Na+ absorbed was compartmentalized in root and shoot, while leaf had more accumulation of K+, that ensured high K+/Na+ ratio in the leaves which is an important salinity tolerant mechanism observed in coconut. The leaf Cl− content also had strong negative correlation with [PN] (r=-0.873) and biomass (r=-0.833), therefore in addition to K+ and Na+ homeostasis, the level of tolerance to the increased Cl− content in the leaves may also play an important role in salinity tolerance of coconut. This understanding will help in making appropriate strategies for managing coconut grown at coastal systems in the face of sea level rise under climate change.

Standardization of rearing techniques and biology of predatory mite, Amblyseius largoenis (muma) on red palm mite, Raoiella indica Hirst and protocol for its field release

The Red Palm Mite (RPM), Raoiella indica Hirst (Acari; Tenuipalpidae) has emerged as a serious pest ofpalms, especially coconut in Trinidad and Tobago, West Indies. Out of the natural enemy fauna recorded, the predatory mite, Amblyseius largoenis (Muma) was found as a potential and most widely occurring predator of red palm mite. Studies were conducted to standardize its rearing technique. Among three types of techniques tested, culturing on the potted coconut seedlings and container method were found to be better option for the mass culturing of A. largoenis over arena method. Besides that the population growth parameters of both prey (RPM) and predator were also studiedand discussed along with feeding potential of A. largoenis. Further, this study will acts as a base line for integrated management practices of R. indica as well as for establishment of laboratory for mass culturing of mites

Kultur Embrio Kelapa Kopyor Menggunakan Beberapa Konsentrasi BA Dan Air Kelapa

Coconut Kopyor is an abnormal fruit, the ordinary coconut flesh is attached to the shell and separated from coconut water while Coconut Kopyor, fruit flesh is not attached to the shell but is mixed with coconut water. Kopyor coconut cannot be used as a seed (seed). The growth of kopyor coconut embryos can only be done in a laboratory with embryo culture technology. Embryo culture is the only way to produce true to type coconut kopyor seeds that can produce 80% kopyor coconut in one kopyor coconut plant, kopyor coconut seedlings produced can support government programs in increasing the productivity of kopyor coconut through the provision of quality seeds. Research on kopyor coconut embryo culture was carried out at the Laboratory of Tissue Culture at Lampung State Polytechnic. The experiment was carried out using a RAL, with 15 treatment combinations of BA media formulations (0, 2, and 4) with coconut water (0 ml / l, 100, 150, 200, 250 ml / l). The observed variables were the percentage of embryos sprouting, when the shoot appeared, shoot height, number of roots, and number of leaves. The results showed that the use of BA 4 mg / l without the addition of coconut water increased the percentage of sprouts, faster time for shoots, and highest shoot height.

Community-level management of bio-resources for augmenting income from coconut-based farming systems in Kerala state, India

On-farm management of farm residues for mass multiplication of beneficial microbes plays an important role in organic farming as well as integrated nutrient management by improving soil health. Community-level production of organic inputs from crop residues can be a potential source of income for farmers’ groups also. A large scale operational research on community-based bio-resource management, along with soil test based nutrient management, was undertaken by ICAR-CPCRI with financial support from NABARD in the major organic tract of Kerala in the coastal belt - Kanjikuzhy block during 2014-2016. The bio-resource management components under technology integration included farm-level production of organics from crop residues, enrichment using bio-agents, utilization of enriched organics for soil and plant health management and production of bio-primed planting materials. For enhancing the efficiency of Trichoderma-enriched organic manure, two ideal media viz., coir pith compost + neem cake (4:1) and coir pith compost + neem cake + poultry manure + cow dung (2:1:1:1) were standardized. Coconut seedlings produced through bio-priming with Trichoderma sp. showed early germination (90%), higher recovery percentage (79.5%), higher collar girth (17 cm), more number of fronds (9) and height (160 cm). Farm-based participatory action management integrating cost-effective bio-resource management interventions in coconut-based farming systems resulted in improvements in income from coconut by 26 per cent and intercrops by 142.9 per cent, contributing to an increase in the average farm income by 149.8 per cent. The average knowledge index of the respondents related to bio-resource management increased by 115.8 per cent and that of integrated nutrient management by 74.5 per cent.

Validation of Diagram Scale for Leaf Spot Caused by Pestalotiopsis sp. in Coconut Seedlings

The absence of a methodology to quantify Pestalotiopsis sp. in coconut plants (Cocos nucifera L.) justified the elaboration and validation of a diagrammatic scale containing seven values (2%, 5%, 10%, 15%, 20%, 40% and 60%) of disease severity, in a sampling under natural conditions of occurrence in the field. To elaborate the diagrammatic scale, 100 leaves of Cocos nucifera L. were obtained from an experimental field of Fazenda Reunidas Sococo in Santa Isabel, Pará. The images of these leaves were obtained with the aid of a digital camera. Subsequently, with the aid of Assess 2.0 APS software, the actual disease severity values were obtained in percentage terms. The validation of the proposed diagrammatic scale was performed by ten inexperienced evaluators who evaluated the projected images without the aid of the suggested scale, and later, with the aid of the scale. From the data obtained from the evaluators with and without scale, linear regression analysis was performed, relating the real severity and the estimated severity. The accuracy of the estimates was evaluated by the regression determination coefficient (R2) and the variance of the absolute errors. The accuracy of each evaluator was determined by the t-test applied to the angular coefficient of line (b) and the linear coefficient of line (a), both obtained by linear regression. Through the coefficient of determination values, It is possible to verify that the use of the scale gave greater accuracy to 100% of the evaluators with an average of 0.94 and 94% repeatability. The use of the diagrammatic spot scale for Pestalotiopsis sp. it enables future work with accuracy and precision, as well as optimizing disease control practices within a coconut tree nursery management program.

Coconut (Cocos nucifera L.) Seedlings Performance in Relation to Rock Phosphate Application in an Ultisol at Nifor Main Station

Coconut (Cocos nucifera L.) Seedlings Performance in Relation to Rock Phosphate Application in an Ultisol at Nifor Main Station

Effects of Dolomite on Some Growth Parameters of Poly Bag Coconut (Cocos nucifera L.) Seedlings in an Ultisol

Effects of Dolomite on Some Growth Parameters of Poly Bag Coconut (Cocos nucifera L.) Seedlings in an Ultisol

First Report of Curvularia oryzae Causing Leaf Spot of Coconut Seedling in China

Coconut (Cocos nucifera L.) is one of the most important perennial tropical crops of southern China. In June 2018, a new leaf spot disease was detected in nearly 100% of 1-year-old golden coconut seedlings at the nursery base in Qionghai, Hainan. At the beginning of the disease, the leaves exhibited water-stained chlorotic spots; as the symptom progressed, the edges of the lesions appeared orange-yellow to pale yellow-brown. Lesions were long oval, almost round, and sometimes irregular with dark brown center and distinct yellow halos. As the lesions continued to expand, several lesions coalesced forming a taupe irregular large spot. The center of the lesion was grayish white, and distinct dark brown necrotic lines were observed at the edges. Under high humidity conditions, thin gray-white mycelia were observed. Overall, 10 leaves with typical symptoms were randomly collected. Small tissue sections (5 × 5 mm) were cut from the lesion margin and surface sterilized in 75% ethanol for 30 s, following which the tissue surface was disinfected with 0.1% HgCl₂ for 2 min, washed thrice with sterile distilled water, plated on potato dextrose agar (PDA), and incubated at 28°C. Five days after incubation, fast-growing fungal colonies with gray-white mycelia were observed, which then changed to dark green with a neat colony edge on PDA medium. Conidiophores were terete, straight or slightly curved, unbranched, often nodular, dilated, and light-to-moderately brown with smooth outer walls. Conidia were 27.1 to 43.3 × 19.0 to 23.4 µm (average 38.1 × 20.1 µm, n = 100), terminal, ovoid, obclavate, and three-distoseptate. The second cell at the base was the largest, taupe to dark brown in color, and often swollen; cells at both ends were slightly smaller and light in color. Based on morphological characteristics, the fungal isolates were preliminarily identified as Curvularia oryzae (Sivanesan 1987). Single-spore isolates were cultured on the PDA medium, and three representative strains were selected for DNA extraction. The identity of the isolates was confirmed via sequence analysis of the internal transcribed spacer (ITS) gene amplified using primers ITS1/ITS4 (White et al. 1990), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene amplified using gpd1/gpd2 (Berbee et al. 1999), and translation elongation factor 1-alpha (EF1a) gene amplified using 983F/2218R (Schoch et al. 2009); sequence data were deposited in GenBank (MN180224, MN180225, and MN481482). BLAST analysis demonstrated that these sequences were 99 to 100% similar to the ITS (MG238513), GAPDH (HG779156), and EF1a (KM196590) sequences of C. oryzae. Moreover, phylogenetic tree analysis using ClustalX and MEGA 7.0 software with the maximum likelihood method placed the isolates in the clade of C. oryzae (CBS169.53) with 98% bootstrap support. Based on the morphology, sequence data, and phylogenetic analysis, these isolates were determined as C. oryzae. To validate the results a pathogenicity test was performed. Twenty leaves were divided into two groups; the first group was sprayed with spore suspension (1 × 10⁶/ml) of the isolate, whereas the other group was sprayed with sterile water as a control. All plants were incubated at 28 ± 2°C and 100% relative humidity. Ten days after inoculation, leaves sprayed with the spore suspension exhibited the typical symptoms with 100% of leaf spot similar to the original samples, whereas leaves sprayed with sterile water showed no symptoms. Further, C. oryzae was reisolated from the leaf spot. Pathogenicity tests were repeated thrice with the same results. Koch’s postulates were achieved by the reisolation of C. oryzae from the inoculated leaves. C. oryzae has previously been reported to cause leaf spot of oil palm seedlings in Thailand (Sunpapao et al. 2014). To the best of our knowledge, this is the first report of leaf spot of coconut seedlings caused by C. oryzae.

Effect of Vermicompost on Growth of Coconut Seedlings under Field Conditions in Sri Lanka

Organic matter contributes in maintaining soil fertility in agriculture. Vermicompost is rich in plant nutrients and recognized as potential organic manure source for many crops. In this experiment, different amount of vermicompost and inorganic fertilizers were tested. The objective of the research was to evaluate the effect of vermicompost on the growth of coconut seedling in the field conditions and to reduce the cost of production of coconut plantations.Treatments were arranged in a Randomized Complete Block Design (RCBD) with three replicates. The experiment consisted of three different fertilizer treatments with vermicompost (100%) + Dolomite 500g (T1), Inorganic fertilizer (Young Palm Mixture) + Dolomite (T2) and vermicompost + Inorganic fertilizer (Young Palm Mixture) + Dolomite (T3). Growth measurements revealed A significantly higher seedling girth, leaf production rate and early highest coconut seedling flowering percentage in the vermicompost base integrated fertilizer applied treatment when compare with other two treatments. This experiment had brought out that application of vermicompost base integrated fertilizer application system is beneficial for coconut seedlings in the field for the better field establishment and vigorous seedling growth.

Isolated and combined effects of soil salinity and waterlogging in seedlings of ‘Green Dwarf’ coconut

Soil salinization is a problem commonly found in semi-arid regions. In addition, the problem of salinity is aggravated in clayey soils when accompanied by cycles of waterlogging in the rainy season or when excess irrigation is applied. In this work we evaluated the isolated and combined effects of soil salinity and waterlogging on the responses of young plants of ‘Green Dwarf’ coconut. The experiment was conducted under controlled environment in a complete randomized block design, arranged in split plots with five replications. The plots comprised five waterlogging cycles (0, 1, 2, 3 and 4), each with a duration of four days, and applied at 30, 60, 90 and 120 days into the experimental period, with the sub-plots consisting of five levels of soil salinity (1.70, 11.07, 16.44, 22.14 and 25.20 dS m-1). Response of coconut seedlings to waterlogging was dependent on the level of soil salinity, with waterlogging significantly impairing biomass accumulation and leaf expansion at low soil salinity levels, but causing no additional harm at elevated salinity. Leaf gas exchange was reduced mainly due to soil salinity, and this response was related to stomatal and non-stomatal effects. Seedlings of ‘Green Dwarf’ coconut used in this study were classified as moderately-tolerant to salinity when grown in soils with an electrical conductivity up to 11.07 dS m-1, having the potential to be used in revegetation programs of salt-affected areas, provided that these areas are not exposed to frequent waterlogging cycles.

English

The aim of this study was to investigate the transmission of the lethal yellowing disease (LYD) of coconut tree caused by a phytoplasma from the zygotic embryo to the regenerated plantlet in vitro. From a total of 30 trees, 150 mature coconut nuts where harvested. These nuts were used to extract 150 zygotic embryos. From this package, 96 zygotic embryos were used to regenerate 96 young coconut seedlings in vitro and the 54 others were used to extract total DNA. From the stem of the 30 palms at the stage 1 of the LYD, phloem sample were also collected. From the regenerated in vitro-plantlets at 6 months age, leaf sample were collected. From the molecular diagnosis by PCR, 80% of the phloem samples carried the 16S rRNA gene of the phytoplasma responsible for LYD. All the zygotic embryos and in vitro-plantlets regenerated were healthy. So, coconut zygotic embryos can be used for the safe exchange of genetic material regarding lethal yellowing disease. The regenerated in vitro plantlet are free of disease. Key words: Coconut, phytoplasma, transmission, in vitro.

Effect of Arbuscular Mycorrhizal Fungi Based Biofertilizer on Coconut Seedlings Growth in Nursery

The success of a coconut plantation, in terms of its field establishment as well as its future performance, is heavily dependent on the quality of the seedlings used. Coconut nurseries adopt different agronomic practices to produce good quality seedlings. Applying mycorrhizal inoculants is becoming an increasingly common practice in plant nurseries as it facilitates healthy seedling growth resulting in healthy and vigorous seedlings in the nursery, helps to reduce mortality rates of seedlings in the field and reduce water and fertilizer consumption. In this study effects of mycorrhizae based biofertilizer were evaluated for the growth of coconut seedlings in the nursery and field. The experiment was conducted at the Makadura Research Center in Sri Lanka. The nursery experiment treatments were, the presence of AMF based biofertilizer (50g per seedling or per bag) and absence of mycorrhizae based biofertilizer. In the field experiment, five treatments with 500g of AMF biofertilizerwith 25% recommended inorganic fertilizer mixture for young coconut palms (YPM) per seedling, 500g of AMF biofertilizer with 50% YPM per seedling, 500g of AMF biofertilizer with 75% YPM per seedling, 500g of AMF biofertilizer with 100% YPM per seedling and with only YPM per seedling. Root and shoot growth of seedlings were measured at monthly intervals in the nursery experiment. Leaf production rate and stem girth of the seedling were measured at six months interval in the field experiment. The application of bio fertilizer increased the volume and dry weight of primary, secondary, tertiary and quaternary roots in seedlings in the nursery significantly. A significantly higher leaf production rate and stem girth was observed in the field seedlings treatment with 500g of AMF biofertilizer with 75% YPM. The experiment concluded that application of bio fertilizer is beneficial for coconut seedlings in the nursery for the production good quality seedlings with well-developed roots resulting in better field establishment and in the field for fast and vigorous growth.