Sri Lanka Tall Research Articles

Physicochemical Properties of Virgin Coconut Oil Extracted from Different Coconut (Cocos nucifera L) Varieties

Virgin coconut oil (VCO) is a superior edible oil extracted from fresh coconut (Cocos nucifera L) kernel using mixed coconut varieties without considering the varietal effect. Therefore, this research focuses on the quality evaluation of VCO extracted from four types of coconut varieties, namely Sri lanka Tall×Tall (TT), a tall variety of Gon Thambili (GT), a tall variety of Ran Thambili (RT) and Philippines tall variety of San Ramon (SR). Mature coconuts from each variety were collected from the Bandirippuwa Estate of the Coconut Research Institute, Sri Lanka to extract VCO by cold press oil extraction method. The extractability of VCO from different varieties was investigated. Moisture, free fatty acid (FFA), fatty acid profile (gas chromatography), peroxide value (PV), color (Lovibond scale), total phenolic substances (Galic acid equivalent), antioxidant capacity (α,α-diphenyl-β-picrylhydrazyl, 0.1mM – DPPH method) and sun protection factor (SPF) of VCO extracted from each variety were analyzed. The experiment was conducted as a completely randomized design with three replicates. Data were analyzed using ANOVA using Tukey’s test by MINITAB 17. Oil extractability (58%-59%), FFA (0.04%-0.12%), color (0.43–0.93) and fatty acid profile of VCO did not show variation among varieties. A higher concentration of total phenolic substances was observed in GT (0.24±0.03mg GAE/100g) while antioxidant capacity (857.19±14.99mg/ml) and SPF (8.99±1.26) was rich in RT.

GENOTYPIC DIFFERENCES IN CARDINAL TEMPERATURES FOR IN VITRO POLLEN GERMINATION AND POLLEN TUBE GROWTH OF COCONUT HYBRIDS

SUMMARYSuccessful fruit set in coconut depends on several reproductive processes including pollen germination and pollen tube growth. High temperature (˃33 °C) during flowering reduces fruit set in coconut. Therefore, identification and development of coconut varieties or hybrids with high reproductive heat tolerance will benefit the coconut industry in view of the climate changes. This experiment was conducted to quantify the response of pollen germination and pollen tube growth of seven coconut hybrids to increasing temperature from 16 to 38 °C. A Principal Component Analysis (PCA) was carried out to classify coconut hybrids on the basis of their temperature tolerances to pollen germination. Pollen germination and pollen tube length of the hybrids ranged from 56 to 78% and 242 to 772 µm, respectively. A modified bilinear model best described the response to temperature of pollen germination and pollen tube length. Cardinal temperatures (Tmin, Topt and Tmax) of pollen germination and pollen tube length varied among the seven hybrids. PCA identified Tmax for pollen germination and Topt for pollen tube length as the most important parameters in describing varietal tolerance to high temperature. PCA also identified SLGD × Sri Lanka Tall and Sri Lanka Brown Dwarf × Sri Lanka Tall as the most tolerant hybrids to high temperature stress and Sri Lanka Tall × Sri Lanka Tall and Sri Lanka Green Dwarf × San Ramon as less tolerant ones based on cardinal temperatures for pollen germination and pollen tube length. Tmax for pollen germination of the most tolerant and less tolerant hybrids were 41.9 and 39.5 °C, respectively. Topt for pollen tube length in the most tolerant and less tolerant hybrids were 29.5 and 26.0 °C, respectively.

Assessing the performance of fruit colour based phenotypes of tall (Typica) coconuts (Cocos nucifera L.) in Sri Lanka

Sri Lanka tall (variety Typica, form typica) is the most widely cultivated coconut form in Sri Lanka. Sri Lanka tall coconuts display variation in fruit colour ranging from green to divergent brownish red (rathi). The growers' perception is that rathi seedlings are more vigorous and higher yielding than the green phenotype. A study was conducted to evaluate and compare the nut and copra yield and seedling vigour of phenotypic groups of green, rathi and intermediate coloured fruits. Secondary data for nut yield recorded over 21 years and husked nut weight of 30 nuts per palm collected over a year in 30 palms in each of the three phenotypes were used for analysis. Furthermore, primary data for seedling girth, height and leaf number in 30 palms each of rathi and green phenotypes were collected for analysis. The data was subjected to Analysis of variance using MINITAB 16. Nut yield or the husked nut weight of the three phenotypes was not significantly different. Significant differences were observed in seedling collar girth between rathi and green phenotypes, with rathi seedlings appearing more vigorous as indicated by the thicker stem compared to the green seedlings. It is concluded that, there are no differences in the nut and copra yield among different colour forms of Sri Lanka Tall coconuts while the rathi seedlings appear superior due to their thicker seedling girth.

Evaluation of coconut germplasm in Weligama and Matara area of the Southern Province of Sri Lanka for resistance to Weligama coconut leaf wilt disease

Weligama Coconut Leaf Wilt Disease has been reported to infect the coconut palms in Southern Sri Lanka. Intra-cellular pathogen phytoplasma has been identified as the causal organism of this disease. So far there have been no known control methods to cure diseases caused by intra-cellular pathogens. Integration of resistant varieties into management programmes has been identified as a viable option in management strategies of such diseases. For this, it is essential to identify the resistance of available genetic resources. This study was carried out in the Weligama and Matara area of Southern Sri Lanka to screen the coconut germplasm for resistance to Weligama Coconut Leaf Wilt Disease. Infected and healthy palms were differentiated using symptomatology; flaccidity of leaves, yellowing of leaves and marginal necrosis of leaflets. Sri Lanka Tall, Sri Lanka Green and yellow dwarfs, Gon thembili tall and king coconut were among the main coconut forms studied. Out of them Sri Lanka Green Dwarf recorded a high level of resistance (98%). Within the Sri Lanka Yellow dwarf and Gon thembili tall, certain individual genotypes were observed to be resistant while king coconut was identified to be susceptible. The most popular commercial coconut variety, Sri Lanka tall was highly susceptible to the disease although there were certain individual genotypes which were resistant. Although Sri Lanka Green dwarf has not so far been viable as a commercial coconut cultivar the presence of resistant genes within the coconut germplasm was recognized as a great advantage in breeding coconuts for resistance to Weligama Coconut Leaf Wilt Disease.

Comparative Evaluation of Sri Lanka Tall and Dwarf x Tall Coconut Hybrids for Tolerance to Weligama Coconut Leaf Wilt Disease in Sri Lanka

Weligama Coconut Leaf Wilt Disease (WCLWD) is a phytoplasma disease found in Southern Sri Lanka. It is an incurable, debilitating disease resulting in yield loss and ultimate death of the palm and over 250,000 palms have been identified to be infected. Breeding coconuts for resistance is a viable option in managing incurable diseases and for this WCLWD resistant germplasm is needed. Accordingly, the objective of the current research was to investigate the comparable levels of WCLWD resistance of Sri Lanka tall and CRIC65 coconut cultivars which are favoured in Sri Lanka.
 Eight coconut estates which were planted with Sri Lanka tall (SLT) and CRIC65 hybrids as a mixed plantation or in close proximity were observed. Out of them an extent of about 04 acres of one estate was selected for detailed analysis using the disease severity index developed based on the WCLWD symptoms; flaccidity, leaf yellowing and marginal necrosis of leaflets.
 General observations indicated the presence of WCLWD in both SLT and the hybrid CRIC65. Marginal necrosis was at a minimal level in both the cultivars, while the other symptoms; flaccidity and yellowing scored higher values at all levels in the spiral in SLT than in hybrid CRIC65. Moreover, the hybrid coconut CRIC65 displayed lower percentage of disease incidence and significant reduction in the levels of the main symptom flaccidity. As a result, the hybrid palms recorded significantly low disease index value than SLT. Moreover, disease incidence was observed to be low in properly managed estates irrespective of the cultivar. With the findings of the current study, coconut varieties SLGD and selected SLT which remain healthy under the same disease pressure can be recommended as parents in a breeding programme aiming at resistance/tolerance to WCLWD.

Genetic diversity of the Sri Lanka yellow dwarf coconut form as revealed by microsatellite markers

Sri Lanka Yellow Dwarf (SLYD) is an important coconut form as a parent in the national coconut breeding programme of Sri Lanka. Though dwarf coconuts are known to be purelines, SLYD displays uncharacteristic morphologies. The current research was conducted to characterize a sample of 15 SLYD individuals using 10 SSR marker loci to determine the genetic diversity within the form. One palm each of Sri Lanka Tall (SLT), Green Dwarf (GD) and Gon Thembili Tall (GT) were used as reference coconut forms. Genomic DNA was extracted and PCR amplification was performed followed by 6% denaturing polyacrylamide gel electrophoresis to visualize the bands. Genotypic data were analysed using PowerMarker software. All ten marker loci were polymorphic, and among them more informative microsatellite loci for the tested population were identified. A total of 34 alleles were scored in the 15 individuals of SLYD ranging from a minimum of two to a maximum of five and a total of 22 heterozygous loci were identified spreading across the ten marker loci. The results indicated the SLYD to share bands more frequently with tall coconut forms than GD. The dendrogram displayed three clusters of SLYD with one group including comparative form GD and another cluster including both SLT and GT. The observed heterozygosity, and genetic and allelic diversities exceed the levels that can be expected from dwarf coconut forms which are self-breeding purelines. It is recommended to purify SLYD coconut form to ensure genetic purity of SLYD parental palm pool in Sri Lanka. Tropical Agricultural Research Vol. 26 (1): 131 – 139 (2014)

Assessment of the Diversity in Fruit Yield and Fruit Components among Sri Lanka Tall Coconut Accessions Conserved Ex-Situ

Characterization of conserved coconut germplasm has been undertaken globally for identification of important features of different accessions for them to be effectively used in coconut breeding. One hundred and fifty seven accessions comprising of local and exotic material have been conserved in ex-situ field genebanks of Coconut Research Institute in Sri Lanka. The objective of this study is to quantitatively characterize nut yield and fruit components by weights among Sri Lanka Tall (Typica) coconut accessions. Twenty local tall coconut accessions were characterized for nut yield and fruit components following Bioversity International descriptors for coconut. Bunch wise nut yield was recorded in all the coconut phenotypes in the six most mature bunches in 25 randomly selected palms from each accession. Sampled nuts were scored for weights of fresh nut, husked nut, split nut and kernel and the weights of husk, water and shell of each nut were derived from the scored data. Analysis of variance by general linear models procedure and mean separation by Duncan’s multiple range test were performed in SAS v8 and principal component analysis and cluster analysis using squared Euclidean distances were performed in Minitab V17. General linear models procedure revealed significant differences for nut yield and all the fruit components at 5% probability level. Walahapitiya recorded the highest average nut yield followed by the Razeena with statistically equal performances. Clovis recorded the highest values for most of the parameters for fruit component analysis followed by the accession Margaret, grouping together in Dendogram and the scatter plot. The highest per nut kernel producer, Clovis, was followed by Margaret with statistically equal performances and this is important because kernel is the main economically important component followed by the husk. Results revealed that there is no significant correlation between nut yield and all the fruit components in tall accessions indicating the importance of taking these two parameters separately to formulate germplasm conservation strategies.

An Investigation of the Tender Nut Potential of Diverse Coconut (Cocos nucifera L.) Varieties/Forms in Sri Lanka

There is a rising demand in the world for coconut water as a healthy natural beverage. Different coconut varieties are used in different countries to be processed as a natural drink. The coconut form “King coconut” has long been used in Sri Lanka as the ideal coconut variety for this purpose. However, with the expansion in the local and export beverage coconut market, the supply does not meet with the demand at present. Therefore, this study was conducted to identify potential coconut varieties/forms mainly relating to the yield of beverage. The study was conducted in the main coconut triangle and Southern Sri Lanka. Eleven coconut forms, namely, King coconut and Bothal thembili in the variety Aurantiaca, Red, Yellow, Green and Brown dwarf and Murusi in the variety Nana, Bodiri, Dothalu, and Sri Lanka tall. These are included in the variety Typica along with Nipol, which is a natural hybrid being identified to be suitable as beverage coconuts. Out of them the yielding ability was high in King coconut, Red dwarf and Yellow dwarf while Bodiri, Nipol and Dothalu fared well. Many coconut forms suitable for beverage purpose were observed to be having seasonality in nut production. Ensuring adequate soil fertility and prevention of water deficit over prolonged periods were observed to help sustain yield and reduce seasonality in bunch emission. There were no large scale plantations for beverage coconuts in Sri Lanka, and the entire collection was from home gardens and very small scale holdings. It is recommended to establish medium scale holdings with coconut forms having high yield potential as identified in the current study, with proper management guidance to ensure a steady supply of beverage coconuts to the local as well as export market.

Molecular Assessment of <i>Cocos nucifera</i> L. Var. Sri Lanka Yellow Dwarf for Genetic Purity and <i>Aceria</i> Mite Tolerance

World-over, coconut is classified broadly into tall and dwarf phenotypes. The dwarf coconut variety is further divided into forms based on the colour of the epicarp. The Sri Lanka Yellow Dwarf (SLYD) coconut variety was observed to have individuals of differing phenotypes and this variety also showed varying degrees of tolerance to Aceria guerreronis (Keifer), which is a pest infesting coconut causing economic losses. This study was aimed at the evaluation of the coconut form SLYD for varietal confirmation and the tolerance to Aceria mite at the microsatellite marker loci. Twenty five sample palms drawn randomly from four morphological groups based on stature and tolerance to Aceria mite were genotyped at seven SSR marker loci along with Sri Lanka Tall (SLT) and Sri Lanka Green Dwarf (SLGD) as reference varieties. Three SSR loci were highly informative for the SLYD population and the results revealed the presence of a population structure within the SLYD coconut population. A clear clustering was observed for tall like and the dwarf like groups with more variation within the tall like group. Clear allelic identifications were established at several SSR loci for the clustering based on stature and the markers were identified for distinguishing different groups. The study provided evidence for the need for reclassification and purification of SLYD coconut population. Certain associations were present for the character Aceria mite tolerance, indicating the potential for marker assisted selection.

Comparison of the Improved Coconut Hybrid CRIC65 with its Reciprocal Cross and the Parental Varieties for Reproductive Traits

Coconut is an important perennial tree crop which offers a multitude of uses. CRIC65 is the first recommended Sri Lankan hybrid coconut cultivar. Sri Lanka Green Dwarf and Sri Lanka tall are respectively, the maternal and paternal parents of CRIC65 and the hybrid is characterized by precocity, high nut yield and fruit component traits. Our objective in this study was to assess the comparative performance of reproductive traits of CRIC65 and its reciprocal hybrid, Sri Lanka Tall x Sri Lanka Green Dwarf with their parental cultivars. The annual nut yield and the fruit components were scored in sixty sample palms representing each cultivar. The field experiment of the two parents were planted in Kurunegala in a favourable site for coconut and the palms were 18 years old at the initiation of data recording. Time taken for flower initiation of the two hybrids and the data of the parental cultivars were extracted from previous records. The data of the two hybrids were analyzed by Student’s t test. Reproductive traits, time taken for flowering and the annual nut yield were not significantly different, while fruit components, husked nut weight, split nut weight and kernel weight recorded significant differences on a few occasions but without identifying a better performer. The two hybrids were clearly different from their parents for the reproductive traits. In conclusion, we report the equal potential of the reciprocal cross (Sri Lanka Tall x Sri Lanka Green Dwarf) of the main recommended hybrid coconut CRIC65 with respect to the most important reproductive parameters that define CRIC65 in favourable sites for coconut in Sri Lanka.

Quantitative Characterization of Nut Yield and Fruit Components in Indigenous Coconut Germplasm in Sri Lanka

Coconut (Cocos nucifera L.) is a tropical palm offering multiple uses. Conservation of coconut germplasm has been undertaken globally in view of its economic importance. This research was designed to evaluate nine Sri Lankan indigenous coconut germplasm representing the three varieties Typica, Nana, and Aurantiaca. Total annual nut yield and the weights of fresh nut, husked nut, split nut, and fresh and dry kernel were scored and analyzed with analysis of variance. The annual average number of bunches varied from 14.9 to 16.8 which is significantly higher than the generally accepted 12–14 bunches in tall coconuts. The high potential of phenotypes Ran thembili and Gon thembili for kernel production was revealed. The high potential of Gon thembili, Sri Lanka Tall, and Ran thembili to produce fibre was also identified. Phenotypes Ran thembili and Gon thembili displayed their potential as pure cultivars and as parents in hybridization. King coconut, Red dwarf, and Bodiri were shown to be suitable as beverage coconuts due to the high production of nuts, bunches, and the quantity of nut water. This study reiterated the importance of conservation and characterization of indigenous coconut varieties globally for their effective use in the genetic improvement of the coconut palm.

Screening Coconut Cultivars for Tolerance to Infestation by the Coconut Mite, Aceria guerreronis (Keifer) in Sri Lanka

The coconut mite (Aceria guerreronis Keifer) is a tiny pest which severely damages the nuts of the coconut palm (Cocos nucifera Linnaeus). At present there is no appropriate control method for this pest in Sri Lanka. Field observations have revealed difference in the severity of A. guerreronis mite infestation among selected and improved coconut cultivars in Sri Lanka. This difference has not been studied in depth and therefore the present study was conducted to investigate the levels of tolerance in selected and improved coconut cultivars and, if differences were demonstrated, to understand the mechanism behind the tolerance. A replicated trial in Thammenna Estate (TE) in Puttalam district in Sri Lanka, where the mite infestation was natural and severe, was selected for this study. The trial was planted in 1983 and consisted of two improved coconut cultivars; Sri Lanka Yellow Dwarf x Sri Lanka Tall (YDT) and Sri Lanka Green Dwarf x Sri Lanka Tall (GDT) and the selected Sri Lanka Tall cultivar (TT) which has, green (TTG) and russet coloured (TTR) forms. Population assessment of mites on immature nuts, damage initiation of the fourth bunch and harvest records were obtained. Further, characters that were thought to influence tolerance, such as nut shape as measured by ratio of length to breadth, the tightness of perianth to the nut surface and some changes in the affected tissues were also recorded. Yield data were collected for each cultivar to estimate the crop loss due to coconut mite damage. The results revealed that out of the cultivars tested in this trial, YDT had the lowest incidence of mite colonization and the smallest mite population size and symptom initiation compared to others. The distance between the perianth and nut surface, the least in YDT, is suggested as the most probable morphological feature that would impart tolerance to mite infestation.

Study on Fatty Acid Composition and Amino Acid Content of Coconut Endosperm of Selected Coconut Cultivars in Thailand

The nutritive values of tropical fruits like coconut are of interest to consumers and useful for the breeding program. The two experiments were carried out in Completely Randomized Design with 3 replications. The first experiment aimed to determine the essential and non-essential amino acid content of liquid and solid endosperm of potential market varieties of coconut such as young tender nut of Aromatic Green Dwarf (Nam Hom) and mature nut of hybrid Nam Hom x Kathi (NHK). Among the 18 kinds of amino acids, the significant differences were found on Aspatic acid, Cystine, Serine, Isoleucine, and Phenylalanine content while highly significant differences were found on Histidine and Methionine content. The second experiment aimed to determine the fatty acid composition of virgin coconut oil of 20 coconut accessions from the coconut field gene bank of Thailand at Chumphon Horticultural Research Centre. The result showed that there were significant differences on the eight fatty acid compositions. Among the eight fatty acids, lauric acid is the most noted one by consumers and it was found that lauric acid content in virgin coconut oil (VCO) was excellent (lauric acid > 48.8%) and the mean of lauric aicd content among the eight varieties had no significant difference at 5% level by DMRT. These varieties include including Renell Tall, Chumphon Hybrid No. 2, Malayan Yellow Dwarf, Sawi Hybrid No.1 (MAWA), Hybrid Chumphon 60, Thai Red Dwarf, Sri Lanka Tall, and Hybrid Nam Hom x Kathi (NHK) with the lauric acid content at 51.0, 50.1, 49.3, 49.0, 49.0, 49.0, 48.9, and 48.8%, respectively. These varieties, therefore, were suitable for VCO processing since they have high lauric content.

Use of Arabinogalactan Proteins in Coconut (Cocos Nucifera L.) Tissue Culture: An Alternative Approach for Improved Tissue Response

Arabinogalactan proteins (AGPs) are extra-cellular proteins involved in plant growth and development. The effects of these proteins on in vitro response of different species are well documented. This study assessed for the first time the role of AGPs on tissue culture of coconut, a highly recalcitrant species in vitro. Coconut (Sri Lanka Tall) plumules were cultured in medium containing 2, 4-dichlorophenoxyaceticacid (2,4-D) for callogenesis. Calli were multiplied by subculturing onto freshly prepared callusing medium. Somatic embryos were induced by transferring of calli to medium with 2/3 concentration of initial 2,4-D and matured by subsequent transferring to medium without any hormones. Embryos were converted in the presence of gibberelic acid. Arabic gum (1-50 mgL-1) was used as the main source of AGP. Alternatively, different AGP sources like Larch wood gum, carrot seeds and defatted coconut kernel were also assessed. Arabic gum in callusing medium resulted in early callogenesis from 20-40% plumules compared to 10% in the control. However, it did not have a significant effect on final callusing efficiency. Its presence in somatic embryogenesis medium showed a significantly higher mass of embryogenic structures per an embryogenic clump (33.3-50.5mg) when compared to the control (26.9mg).The best result was obtained at 10mgL-1 Arabic gum. All AGP sources except Larch wood gum had positive effects on somatic embryogenesis. Among them, defatted coconut kernel (25-50mgL-1) showed the best results giving 70% cultures with embryogenic structures compared to 37% in control. However, so far, the positive effect of AGP did not reflect in plant regeneration efficiency.

GENETIC IMPROVEMENT OF THE COCONUT CULTIVAR SAN RAMON

The tall form of coconut, San Ramon was imported to Sri Lanka fromthe Philippines and was first established in the North Western Province. Theopen pollinated seed obtained from the first introduction and planted at theCoconut Research Institute (CRI), form the genetic base for San Ramonimprovement at present. This cultivar inherits the potential of producing 51 %more copra per nut than Sri Lanka Tall palms and 50% more copra per nutthan the improved tall, CRIC 60. The mean copra yield per nut recorded forSan Ramon (selfed), Sri Lanka Tall and CRIC 60 was 371 g, 240 g and 246 grespectively. Preliminary investigations have shown that the oil extractionefficiency of copra is 776 ml per kg of copra for Tall x San Ramon whilst forboth Sri Lanka tall and CRIC 60, it is 740 ml. The results of this studystrongly justify the use of San Ramon and its crosses for copra and oilindustry in Sri Lanka.

Hybrid Testing and Variety Identification of Coconut (Cocos nucifera L.) in Sri Lanka Using Microsatellite Markers

Currently, there is no reliable method for confirmation of the identity of coconut cultivars and the legitimacy of coconut hybrids. This makes serious problems in coconut breeding and seed production as the identity of coconut cultivars/hybrids can only be approximated at the very late stages of the growth based on reproductive traits owing to long juvenile period and the perennial nature of coconut. A microsatellite (SSR) marker based approach was used to develop an identification method for coconut varieties; Sri Lanka Tall, Sri Lanka Green Dwarf and Sri Lanka Yellow Dwarf, the key parents in the breeding programmes and tall x dwarf hybrids among them, using 18 coconut specific SSR primers. The validity of using yellow colour petiole as a phenotypic marker for the identification of dwarf yellow was also investigated. Two SSR primers, namely CAC20 and CNZ6 have exhibited the potential for distinguishing coconut varieties used as parents in the breeding programme and for confirming hybridity. It was revealed that yellow colour petiole is not a reliable marker for identification of dwarf yellow variety.

MICROPROPAGATION OF COCONUT THROUGH PLUMULE CULTURE

Plumule tissues have found to be more responsive explants for clonalpropagation of coconut. In the present study, the feasibility of using plumuleexplants for clonal propagation of a local coconut variety (Sri Lanka Tall)was assessed. Plumules were cultured in three basal media (MS, Y3 and72) supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) (24 - 400 \M)and activated charcoal. Somatic embryogenesis and plant regenerationwere induced by incorporating of abscisic acid (ABA) into the medium.Attempts were made to improve plant regeneration by applying high agarconcentration-induced water stress, cytokinin or silver nitrate in combinationwith ABA.The results revealed that callus can be initiated from plumule explantscultured in all three basal media tested. The callus formation depended onthe concentration of 2,4-D in the media and the best effect was observedwith the lower level (24 jiM) tested. The plant regeneration frequencyobserved with ABA treatment was 4.4 %. The combination of ABA with highagar concentration-induced water stress doubled the plant regenerationfrequency. About 50 % of the regenerated plants could be successfullyacclimatized and field planted.The results of the study indicate the possibility of regenerating plants fromplumule explants of coconut. The method can be used for multiplication ofimproved seed material. However, the plant regeneration efficiency shouldbe further improved for mass scale propagation of coconut using plumuleexplants.

Effect of Abscisic Acid on Survival and Recovery of Cryopreserved Plumule Explants of Coconut (<i>Cocos nucifera</i>)

Cryopreservation has great potential for long-term storage of coconut genetic resources. The recent development of the encapsulation-dehydration cryogenic technique dramatically facilitated progress with cryopreservation. The present study tested the effect of abscisic acid in the encapsulationdehydration method for cryopreservation of coconut plumules. Plumules were excised from mature zygotic embryos of Coconut var. Sri Lanka Tall and encapsulated in calcium alginate. The alginate beads were used to test effect of different cryoprotection pretreatments (mixtures of 0.75 M sucrose and abscisic acid (ABA) at concentrations of 0, 10, 20 and 40 μM), and exposure to silica gel for 16 hours for further dehydration, prior to freezing in liquid nitrogen. Effect of the treatments without freezing was also tested. The water loss from alginate beads following sucrose incubation and dehydration was monitored, and the survival and growth of plumules assessed at different stages. Addition of ABA to the sucrose pretreatment medium increased the survival rate of unfrozen plumules from 60% to over 80%. Pretreatment with 40 μM ABA gave the highest survival rate (84%) of frozen plumules. The recovery rate of plumules (frozen and unfrozen) pretreated without ABA was very low (6-8%). The addition of ABA increased the recovery rate significantly; frozen plumules that had been treated with 40 μM ABA recorded a 39% recovery rate. The improved recovery could be ascribed to increased water loss (69%) in plumules treated with 40 μM ABA. Key words: Coconut, plumule, cryopreservation, abscisic acid doi: 10.4038/cocos.v18i0.989COCOS (2007), 18

Androgenic potential in coconut (Cocos nucifera L.)

Conditions for induction of androgenesis in coconut cv. Sri Lanka Tall were studied. Anthers collected from inflorescences at four maturity stages were given heat (38°C) or cold (4°C) pretreatments for 1, 3, 6 and 14 days, either prior to or post inoculation. Three different basal media and different anther densities were also tested. Androgenesis was observed only in anthers collected from inflorescences 3 weeks before splitting (WBS) and after a heat pretreatment at 38°C for 6 days. Modified Eeuwens Y3 liquid medium supplemented with 100 μM 2,4-dichlorophenoxyacetic acid (2,4-d), 0.1% activated charcoal and 9% sucrose was effective in inducing an androgenic response. The lowest anther density tested, 10 per petri plate, was found to be the optimal density. When androgenic calli or embryos were subcultured to Y3 medium containing 66 μM 2,4-d, followed by transfer to Y3 medium without plant growth regulators and finally to Y3 medium containing 5 μM 6-benzyladenine (BA) and 0.35 μM gibberellic acid (GA3), plantlets regenerated at a frequency of 7%. Histological study indicated that the calli and embryos originated from the inner tissues of the anthers. Ploidy analysis of calli and embryos showed that they were haploid. This is the first report of successful androgenesis yielding haploid plants from coconut anthers.

Plant structural changes due to herbivory: Do changes in Aceria-infested coconut fruits allow predatory mites to move under the perianth?

Being minute in size, eriophyoid mites can reach places that are small enough to be inaccessible to their predators. The coconut mite, Aceria guerreronis, is a typical example; it finds partial refuge under the perianth of the coconut fruit. However, some predators can move under the perianth of the coconut fruits and attack the coconut mite. In Sri Lanka, the phytoseiid mite Neoseiulus baraki, is the most common predatory mite found in association with the coconut mite. The cross-diameter of this predatory mite is c. 3 times larger than that of the coconut mite. Nevertheless, taking this predator’s flat body and elongated idiosoma into account, it is—relative to many other phytoseiid mites—better able to reach the narrow space under the perianth of infested coconut fruits. On uninfested coconut fruits, however, they are hardly ever observed under the perianth. Prompted by earlier work on the accessibility of tulip bulbs to another eriophyoid mite and its predators, we hypothesized that the structure of the coconut fruit perianth is changed in response to damage by eriophyoid mites and as a result predatory mites are better able to enter under the perianth of infested coconut fruits. This was tested in an experiment where we measured the gap between the rim of the perianth and the coconut fruit surface in three cultivars (‘Sri Lanka Tall’, ‘Sri Lanka Dwarf Green’ and ‘Sri Lanka Dwarf Green × Sri Lanka Tall’ hybrid) that are cultivated extensively in Sri Lanka. It was found that the perianth-fruit gap in uninfested coconut fruits was significantly different between cultivars: the cultivar ‘Sri Lanka Dwarf Green’ with its smaller and more elongated coconut fruits had a larger perianth-fruit gap. In the uninfested coconut fruits this gap was large enough for the coconut mite to creep under the perianth, yet too small for its predator N. baraki. However, when the coconut fruits were infested by coconut mites, the perianth-rim-fruit gap was not different among cultivars and had increased to such an extent that the space under the perianth became accessible to the predatory mites.