Oil Palm Roots Research Articles

Development of integrated factor modeling: Inhibiting Ganoderma lignocellulosic enzymes while promoting Trichoderma sporulation for enhanced plant disease control

Ganoderma, a fungal pathogen, is the causal agent for basal stem rot disease in oil palms, which has led to significant losses in palm oil production. The fungal production of lignocellulosic enzymes is crucial for successful infection, hence the disease severity could be significantly reduced by inhibiting these enzymes. The current study investigated the impact of integrated factors on inhibiting these enzymes and promoting Trichoderma virens spore production using response surface methodology. The identified optimal conditions of temperature (27.5–36.5 °C), boron (0.07–0.30 mg/mL), potassium (3.5 mg/mL), and mancozeb (1.0 mg/mL) can lead to the production of ≥5.0✕105 spores/mL of T. virens, while minimizing the laccase, cellulase, and xylanase activities to ≤0.08, 0.0, and 0.0 U/mL, respectively. The model's prediction accuracy was 81.25 %. In a greenhouse application, soil temperature was increased to 43.7 °C by solarization before applying the optimal concentration of boron, potassium, mancozeb, and T. virens. The results demonstrated the inhibition of lignocellulosic enzymes in G. boninense, as indicated by 69.0 % and 68.7 % lignocellulose contents in Trichoderma-treated and Ganoderma + Trichoderma-treated oil palm roots, respectively, which were higher than that in Ganoderma-treated roots (58.1 %). This highlights the practical relevance of our findings. Therefore, these results will help the oil palm growers to develop disease management strategies to control basal stem rot.

An interesting phenomenon in oil palm: anatomical, morphophysiological, and biochemical observations from aerial roots on the trunk

Abstract Roots are plant organs that function for nutrient and water absorption and support plant upright. Oil palm has distinctive roots due to the growth of primer roots that grow in two directions, namely vertical and horizontal. The growth of oil palm roots is highly dependent on the source of energy accumulated at the base of the stem. The availability of assimilate will determine the rate of root formation. The results of observations in the field, there is a phenomenon of root growth on oil palm stems. In general, there are four root growth phenomena, namely aerial roots which are the roots of plants affected by Ganoderma disease, roots that grow in the middle of the stem, the base of the stem, and at the end of the stem of the oil palm plant. This phenomenon has not been studied comprehensively. Therefore, this study was conducted with the aim of identifying the anatomical, morphophysiological, and plant biochemical observations of normal and aerial roots in oil palm trunks. The results showed differences in anatomical, morphology, and biochemical between roots growing underground and aerial roots. There are anatomical differences between the actual and aerial roots, namely the number of meta xylem is 19 pieces with a larger size in the underground roots, while the aerial roots are only 15 with a smaller size. The similarities between the two roots are included in the scalariform group. Aerial roots have the same types of roots as normal, namely primary, secondary, and tertiary roots. Based on the biochemical analysis, Palm5 has 3 times higher than reducing sugar percentage on Palm7.

The suppression of Ganoderma boninense on oil palm under mixed planting with taro plants

Abstract. Suwandi S, Alesia M, Munandar RP, Fadli R, Suparman S, Irsan C, Muslim A. 2024. The suppression of Ganoderma boninense on oil palm under mixed planting with taro plants. Biodiversitas 25: 1143-1150. Basal stem rot, caused by Ganoderma boninense, is highly destructive in monoculture oil palm plantations. This study evaluated Ganoderma boninense infections and oil palm growth in mixed plantings of oil palm seedlings and taro plants (Japanese, Bogor, and Indralaya taro). Ganoderma, colonizing rubber wood blocks, was inoculated into mixed plants, and the infection was compared to single-inoculated oil palm and taro plants. The interference of mixed planting with taro plants on the growth of oil palm seedlings was compared between inoculated and noninoculated mixed and single planting. Ganoderma inoculation caused simultaneous disease (dual-host infection) in mixed oil palm and taro plants. Ganoderma infection was less severe in taro plants compared to oil palm, whether in single or mixed planting. Over six months, oil palm root necrosis and disease index were reduced by 82% to 96% and 65% to 71%, respectively, while no significant effect was observed at nine months. The decay of Ganoderma-colonized wood improved by 44.1% to 84.0% in mixed planting, with no significant impact on mycelium viability. Taro plants did not inhibit oil palm growth, including plant height, leaf area, and relative growth rate of primary root length, in both the presence and the absence of Ganoderma infection. This study highlights the potential of mixed planting with taro to reduce Ganoderma disease in oil palm.

Study of Laccase Activity as a Biosensor for Peatland Degradation in Oil Palm Plantations in Pesisir Selatan of West Sumatra

The aim of the research was to study enzyme activity as biosensors for peatland degradation in oil palm plantations. The study was conducted in Pesisir Selatan,West Sumatra, on two peatlands with different thicknesses and location coordinates, namely peat with a thickness of <3 m S: 02o18'45.5", 101o00’37.3” and peat with a thickness >3 m S: 02o20’07.5”, E: 101o00’22”. The oil palm in these two locations is 11 years old (planting year of 2007). Observations and sampling of peatlands were carried out on the plantation blocks using the transect method. The transect was set perpendicular to the drainage canal. Peat samples were collected outside the roots (non-rhizosphere) of oil palm. Observation sites were at a distance of 5, 15, 25, 50, 75, 100, 150 m from the edge of the drainage canal and at the thickness of the root layer of 0-25 and 25-50 cm. Peat characteristics observed were water table level, laccase activity, water content, pH, total Fe, and Cu. The water table level in one transect ranged from 60-80 cm and was still within tolerable limits. The laccase activity as a peat degradation biosensor in oil palm plantations in Pesisir Selatan peatland was higher in the 0-25cm layer with an average of <0.5 µmol/g. The increase in water content decreased the laccase activity along with increasing of the distance from the drainage canal and the thickness of the peat layer. The increase in Fe and Cu resulted from increased levels of ash, particularly in peat with a thickness of <3 m, may suppress laccase activity. Peatland in the oil palm plantation of Pesisir Selatan is still relatively stable despite the decomposition processes characterized by laccase activity as a biosensor for peat degradation.

RESPON PEMBERIAN PUPUK HAYATI BIONEENSIS TERHADAP PERTUMBUHAN JUMLAH MATA TUNAS TANAMAN JAHE MERAH

Ginger is an agricultural commodity that has good opportunities and prospects for development. Bioneensis biofertilizer contains bacteria isolated from oil palm roots and has many benefits for plants. This study aims to determine the effect of biofertilizer application bioneensis on the growth of the number of shoots and the production of red ginger (zingiber officinale var. Rubrum). This study used a factorial randomized blok design with 2 factors and 3 replications. Giving bioneensis (B) consists of 4 levels, namely B0 (0 gr/polybag), B1 (20gr/polybag), B2 (40 gr/polybag), and B3 (60 gr/polybag). The number of buds consists of 4 levels, namely M1(1 mata tunas), M2 (2 mata tunas), M3 (3 mata tunas), and M4 (4 mata tunas). The results of the study gave a very significant effect on the parameters, namely plant height (cm) and the effect was not significant on parameters, number of leaves (helai), number of tillers per polybag, and canopy dry weight (gr). While the results of the study on the application of biofertilizer bioneensis and the number of buds showed no significant effect on all parameters, namely plant height (cm), number of leaves (helai), number of tillers per polybag, and canopy dry weight (gr). The best treatment was found in the parameters of plant height with a dose of 60% bioneensis and the number of shoots 2 with an average yield of 77.17 cm.

Xylem Vessels Traits of Oil Palm Roots Influenced by Root Diameter and Soil Hydrological Regime

Oil palm has been widely studied regarding growth and development, water use, productivity, and other economically relevant functions. However, not much is known about the hydraulic conductivity of oil palm root systems and how xylem vessels perform their function to transport water from roots to shoots so far. This information is needed to describe oil palm strategies to maintain water status, especially in oil palms that grow under various soil hydrological regimes. To investigate the root hydraulic performance, we measured mean xylem vessel diameter (D), vessel density (VD), vessel lumen area (Alumen), and potential hydraulic conductivity (Kp) for oil palm root samples in seasonally flooded riparian and well-drained sites at Harapan Jambi Forest. The result showed that D, Alumen, and Kp increased with increasing root diameter at both plantation types. On the contrary, VD significantly decreased with increasing root diameter. Potential hydraulic conductivity (Kp) in riparian sites was smaller than in well-drained sites and significantly different in root diameter >2-5 and >5-10 mm and related to both plantation types. The low potential hydraulic conductivity of root xylem vessels and the narrowing of xylem vessel lumen that occurs in oil palm roots in the seasonally flooded riparian sites were presumed as adaptation mechanisms to maintain water supply from the roots to the shoot in oil palm plants in these sites.

Molecular network of the oil palm root response to aluminum stress

BackgroundThe solubilization of aluminum ions (Al3+) that results from soil acidity (pH < 5.5) is a limiting factor in oil palm yield. Al can be uptaken by the plant roots affecting DNA replication and cell division and triggering root morphological alterations, nutrient and water deprivation. In different oil palm-producing countries, oil palm is planted in acidic soils, representing a challenge for achieving high productivity. Several studies have reported the morphological, physiological, and biochemical oil palm mechanisms in response to Al-stress. However, the molecular mechanisms are just partially understood.ResultsDifferential gene expression and network analysis of four contrasting oil palm genotypes (IRHO 7001, CTR 3-0-12, CR 10-0-2, and CD 19 − 12) exposed to Al-stress helped to identify a set of genes and modules involved in oil palm early response to the metal. Networks including the ABA-independent transcription factors DREB1F and NAC and the calcium sensor Calmodulin-like (CML) that could induce the expression of internal detoxifying enzymes GRXC1, PER15, ROMT, ZSS1, BBI, and HS1 against Al-stress were identified. Also, some gene networks pinpoint the role of secondary metabolites like polyphenols, sesquiterpenoids, and antimicrobial components in reducing oxidative stress in oil palm seedlings. STOP1 expression could be the first step of the induction of common Al-response genes as an external detoxification mechanism mediated by ABA-dependent pathways.ConclusionsTwelve hub genes were validated in this study, supporting the reliability of the experimental design and network analysis. Differential expression analysis and systems biology approaches provide a better understanding of the molecular network mechanisms of the response to aluminum stress in oil palm roots. These findings settled a basis for further functional characterization of candidate genes associated with Al-stress in oil palm.

Understanding the effects of carbon and nitrogen starvation on the comparative secretomes of Ganoderma boninense and Ganoderma tornatum

Ganoderma boninense is the most pathogenic fungal species of oil palm trees. However, there is limited understanding of the host - pathogen interaction. Secreted proteins play a critical role during the early infection process which involves competition between the fungal and host populations for nutrient resources necessary for continual growth. To identify the secreted proteins that may play a role in pathogenicity during infection stage, we compared the secretome profiles of G. boninense versus G. tornatum under carbon and nitrogen starvation by using shotgun proteomics approach. In total, 250 non-redundant proteins were identified, and statistical data analysis indicated that 68 proteins were increased while 104 proteins decreased in abundance in T3 for G. boninense whereas in G. tornatum, 42 proteins were increased, and 27 proteins were decreased in abundance in T3. Further investigation via bioinformatic tools helped us to classify the carbohydrate-active enzymes (CAZymes) proteins into four classes: oxidoreductases, transferases, hydrolases, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Interestingly, oxidoreductase enzymes were identified only in G. boninense. These putative proteins might contribute to the different levels of pathogenicity of G. boninense and G. tornatum toward oil palm. The newly discovered protein information may help researchers better understand the secretory mechanisms of G. boninense and the process by which it invades oil palm root tissues. The discovered seretome proteins, along with their subclassification and functional annotation also serve as a database for Ganoderma species that is easy to access and retrieve.

Identification of microRNAs involved in the Phosphate starvation response in Oil Palm (Elaeis guineensis Jacq.).

Plant microRNA, often known as miRNA, is a novel form of gene expression regulator that is known to play a significant role in phosphate starvation. The identification of microRNAs involved in the response to phosphate starvation in oil palms is beneficial for breeding programs. The main nursery stage seedlings of two oil palm progenies were treated with three different fertiliser namely: complete fertiliser with urea, P2O5, K2O, and MgO based on the standard procedure as a control (C); fertiliser with urea, K2O, MgO without P2O5 (P0); and no fertiliser (F0) for 24weeks. A total of six oil palm roots were subjected to RNA isolation, followed by miRNA sequencing using the Illumina HiSeq 4000 platform, and all reads were computationally analysed. In total, 119 potential miRNAs related to 5,891 genes were identified. The P-specific miRNAs were assumed based on the miRNAs that identified without P fertilizer treatment, resulted of twenty miRNA sequences in the treatment comparison of (C vs P0) vs (C vs F0). Those 20 miRNA sequences were grouped into 9 families, namely EgmiR319; EgmiR399; EgmiR396; EgmiR172; EgmiR156; EgmiR157; miR5648; miR5645; and EgmiRNA_unidentified. Two miRNAs were selected for RT-qPCR validation, namely EgMir399 and EgMir172. Their expression pattern was similar with the RNA sequencing results and shown opposite expression pattern with their target genes, UBC E2 24 and APETALA2, respectively. The nine micro RNA families was identified in oil palm root tissue at phosphate starvation.

Validation of Early Infection Markers for Ganoderma in Oil Palm at Three Endemic Ganoderma Locations

A serious disease that affects the viability of the oil palm industry is basal stem rot, which is caused by Ganoderma. The current level of disease can be viewed as unmanageable, given that the palms were growing in an unfavorable or unsuitable climate. Today, there are numerous approaches to diagnose diseases early, and one of them using molecular methods. Seven genes for early infection markers were effectively generated by a reference's transcriptome study, including LEUCO, ETHYLENE, CHALCONE, ANTHOCYANIDIN, ETHYLENE, MANNOSE, and SENESCENCE. The purpose of this study is to validate and confirm the presence of Ganoderma infections in three endemic oil palm field in Indonesia i.e. Cisalak Baru, Rejosari, and Bekri plantation. This study conducted real time qPCR of RNA from oil palm roots with four different severities of infection. Manual processing of RNA isolation and cDNA synthesis were carried out, to provide quantification expression level. In addition, gene ontology (GO) analysis was also performed in order to explain the roles of each gene tested. The results revealed that CHALCONE is the only marker that consistently elucidate the Ganoderma's early infection appear in three locations. The drawbacks of the analysis results are tightly correlating to the age of oil palm as well as endemic location. GO results declare that seven genes function related to the response of infection. This work was successful in confirming early infection in three places, elucidating the variables influencing the efficacy and sensitivity of molecular detection, and revealing the function and importance of particular genes for detection.

Comparative Genomics Analysis of Ganoderma Orthologs Involved in Plant-Pathogenesis

Ganoderma species are producers of bioactive secondary metabolites and lignin degraders. A few Ganoderma species are known to be plant pathogens that attack economically important trees. In this study, comparative genomics analysis was conducted on the proteome of ten Ganoderma species/strains, focusing on the proteins that have been reported to be involved in plant-pathogenesis in other fungi. Fungal trophic lifestyle prediction of these Ganoderma species/strains supported that G. boninense (a potent pathogen to oil palm) is a hemibiotrophic fungus while the other Ganoderma species/strains analyzed were predicted to be saprophytes or a symbiont based on their Carbohydrate-Active Enzyme (CAZyme) contents. Although these Ganoderma species/strains were demonstrated to share many CAZymes and secondary metabolite core gene clusters, individual species may produce unique CAZymes and secondary metabolite core genes that determine their lifestyles, host-specificity, and potential as a producer of bioactive secondary metabolites. Ortholog groups that are related to fungal virulence from seven Ganoderma species/strains including those involved in lignin degradation, mycotoxin, siderophore and ergosterol biosynthesis, and virulence were summarized. Potential effectors were predicted from the proteome of these Ganoderma species/strains, and putative effectors that were being expressed in G. boninense in oil palm roots but not found in other species were identified. The findings provide a useful resource to further analyze plant-pathogenesis and wood degradation activities of these Ganoderma species.

Expression of genes related to hydrogen peroxide generation and phytohormones in Ganoderma-inoculated oil palm seedlings pretreated with phytohormones and their inhibitors

Hydrogen peroxide, salicylic acid (SA) and jasmonic acid (JA) are reported to play important role in plant defense responses against pathogens. In this study, we analyzed the transcript abundance of oil palm respiratory burst oxidase B (EgRbohB1) and H (EgRbohH), Coronatine Insensitive 1 (EgCOI1), OPR5 (EgOPR5), hypersensitive induced response 1 (EgHIR1) and Nonexpressor of pathogenesis-related (EgNPR1) in Ganoderma boninense-inoculated oil palm roots that were pretreated with SA, JA and their inhibitors, paclobutrazol (PAC) and diethyldithiocarbamate (DIECA), respectively. We showed that EgNPR1 was down-regulated by G. boninense infection in SA-pretreated oil palm roots while EgHIR1 was up-regulated by G. boninense in PAC-pretreated oil palm roots. G. boninense inoculation did not change the gene expression levels of EgOPR5 in JA- and DIECA-treated oil palm roots significantly, compared to the uninoculated oil palms roots that were treated similarly. EgCOI1 was up-regulated by G. boninense in JA- and DIECA-pretreated oil palm roots, respectively. G. boninense up-regulated EgRbohB1 in SA-pretreated oil palm roots but down-regulated it in PAC-pretreated oil palm roots. EgRbohH was also down-regulated by G. boninense in PAC-pretreated oil palm roots. These findings facilitate the understanding of phytohormone effects on oil palm-Ganoderma interaction.

The effectiveness of acid-tolerant antagonists in the control of oil palms root necrotic caused by Ganoderma sp. in peat soils

Oil palm is the main plantation commodity in Indonesia. In the last two decades, Indonesian palm oil has always been associated with global warming because most of its plantation areas are located on peatlands and the cultivation method is considered not environmentally friendly. One of the problems of oil palm cultivation on peatlands is stem rot disease caused by the fungi Ganoderma sp. This disease is transmitted through root contact. There is no effective way to control this disease. Biological control is an alternative method that is environmentally friendly. This study aims to determine the effectiveness of acid-tolerant antagonists in controlling oil palm root necrotic on peat soils. The study tested 5 isolates of the acid-tolerant antagonists in reducing oil palm root necrosis caused by Ganoderma on peat soils in experimental gardens. The results showed that the acid-tolerant antagonists were effective in controlling root necrosis in oil palm seedlings on peat soils. Its effectiveness reached 16.67%. Differences in peat soil pH and peat maturity did not affect the effectiveness of root necrotic control caused by Ganoderma sp. These results indicate that using acid-tolerant antagonistic fungi can help reduce Ganoderma sp attacks on oil palms on peat soils.

Co-infection of two Ganoderma boninense strains on oil palm seedlings

Ganoderma boninense is the basal stem rot disease (BSR) pathogen that devastates oil palm plantations. Disease infection generally occurs by a single strain of G. boninense, or co-infection of two strains arises as revealed by somatic incompatibility. This study aimed to determine the effects of co-infection of two somatically incompatible G. boninense strains on the BSR disease of oil palm seedlings. Two strains of G. boninense were from 2 oil palm plantations and had different aggressiveness. Co-infection of two G. boninense strains was performed by inoculating the Ganoderma rubber wood blocks to the 3-month-old oil palm seedling and examined for 7 months. The results showed that co-infection with two G. boninense strains had similar disease symptoms, decreased disease severity (score 1.5 compared to 2.0 for a single aggressive strain), and similar seedling growth retardation by the single aggressive strain. Higher fungal colonization (92%) of oil palm roots was exhibited in the co-infection compared to 85‒86% colonization of a single strain infection. This study revealed that co-infection with two somatically incompatible strains might favor host colonization by G. boninense.

UJI BEBERAPA ISOLAT JAMUR ENDOFIT TERHADAP JAMUR TULAR BENIH DAN PERTUMBUHAN BIBIT CABAI MERAH

The aim of this study was to test several endophytic fungi isolates with high antagonistic power against seed borne fungi in vitro and their effect on the growth of chili (Capsicum annuum L.) seedlings in vivo. This research was conducted at the Plant Disease Laboratory and Greenhouse Faculty of Agriculture, Riau University from October 2018 to February 2019. This research was conducted experimentally using a completely randomized design (CRD) consisting of 5 treatments and 4 replications. The treatment of endophytic fungi was applied using the seed immersion method. The results showed that giving the endophytic fungi Rhizictonia sp., Cephaloporium sp., T. virens from oil palm roots and T. virens from oil palm stems were able to suppress the incidence of seed-borne pathogenic fungi Fusarium sp., Colletotrichum sp. and Aspergillus sp.. Provision of endophytic fungus T. virens from oil palm roots can increase seed germination capacity by 14%, number of live seeds by 17% and increase seedling height and leaf number.

IMPACT OF FERTILISER APPLICATION ON BASAL STEM ROT AND LOWER FROND DESICCATION IN OIL PALMS ESTABLISHED IN PEAT SOIL

For oil palms established in deep peat soils in the Labuhan Batu district, North Sumatra, Ganoderma basal stem rot (BSR) and lower frond desiccation (LFD) are the two main maladies that have a serious impact on their long-term sustainability. Past experiences have shown that solitary control measures are unlikely to be successful in managing these two maladies and a number of integrated control strategies would be a prerequisite for their management. As nutrition is an important factor influencing fungal disease infection in many crops, nutrient manipulation can be considered as a vital component of any integrated disease management (IDM) system. This paper summarises the impact of fertiliser application on the level of BSR and LFD infection in five fertiliser trials, established in the affected areas from 1996-2021. In both trials established on first and second generation oil palms, application of nitrogen (N) and phosphorus (P) elicited a significant and linear increase in BSR infection levels, the higher the dosage, the higher the BSR incidence. In contrast, potassium (K) inputs had the reverse effect and significantly reduced BSR infection in the first trial but not in the second. A significant negative additive interaction between N x P and P x K was also observed in both trials. Increasing the rates of N together with P or P with K, increased BSR infection, with the highest infection levels being recorded at the highest N2P2 and P2K2 rates evaluated. Unlike macronutrients, application of boron (B), copper (Cu) and zinc (Zn) micronutrient fertilisers did not have any significant impact on BSR incidence. A similar trend was recorded on LFD incidence in both immature and mature second generation oil palms. Application of N and P also elicited a significant and linear increase in LFD and a strong negative and additive interaction effect between N x P and P x K was also observed. As for BSR, impact of K fertiliser was inconsistent, producing no positive or negative effects in immature palms and only significantly reducing LFD levels in two out of the 6 years of evaluation in mature oil palms. Likewise, application of B, Cu and Zn micronutrient fertilisers also had no impact on LFD incidence. Although peat is reported to be low in silica, application of silica fertilisers, even up to a dosage of 6 kg per palm per year produced no positive benefits. The relationship between nutrients and BSR/LFD infection and the physiological and biochemical mechanisms involved, remains unclear. However, it is interesting to note, that in all three NPK trials, the lowest infection rates were consistently recorded in the zero fertiliser plots. A possible hypothesis is that long-term application and concentration of N and P fertilisers in the weeded palm circles (WPC) could have had a negative impact on beneficial soil microbes inhabiting the root rhizosphere and associated with oil palm root protection or inducing systemic resistance in the oil palm. However, more detailed studies are required to ascertain the complex relationship between nutrients, soil microbes and disease infection. Keywords: Basal stem rot, fertilisers, lower frond desiccation, oil palm, peat.

CO2 MEASUREMENT IN PALM OIL PLANT IN PEATLAND

Peatlands are one of the contributors to greenhouse gas emissions because it is estimated that the carbon stock stored in them is around 528 Giga tons (Gt) or equivalent to 75% of the total carbon (C) in the atmosphere, so that if peat is oxidized it will cause carbon to be released into the air. The conversion of forest land to agricultural land can be one of the causes, including the activity of making drainage channels. The construction of drainage channels causes a decrease in the water table so that the volume of peat under aerobic conditions increases while increasing the activity of microorganisms in decomposing peat. Peat decomposition and root respiration contribute to carbon emissions. This study aims to determine the CO2 concentration in several conditions of oil palm roots. CO2 measurement by survey method on oil palm plantations, using the IRGA (Infra Red Gas Analyzer). Measurements are carried out once per month from January to May 2020 for 3 minutes. The point of observation was determined by 2 factors with 3 treatments and 3 replications. Factor 1 is the observation point in the area of accumulation of midrib pieces and other litter (B1) and factor 2 is the observation point in the road area around the tree (B2). While the treatments were (A1) natural roots, (A2) roots were cut when the measurements were going to be taken and (A3) roots were cut and permanently restricted. The results of the measurement of the highest average concentration of CO2 changes from 0 minutes to 3 minutes in January were in treatment B1A3 (140.4 ppm), February in treatment B2A3 (103.9 ppm), March B1A3 (124.6 ppm) ppm), April B1A3 (143.8 ppm) and May B1A3 (110.7 ppm). Meanwhile, the lowest concentration of CO2 changes from 0 minutes to 3 minutes in January was in treatment B1A1 (71.5 ppm), February in treatment B1A1 (25.7 ppm), March B2A3 (40.2 ppm), and March B2A3 (40.2 ppm). April B2A1 (30.6 ppm) and May B1A1 (43.2 ppm). From the measurement results, it can be concluded that the highest concentration of CO2 and its changes was in treatment B1A3, namely in the treatment of cutting roots with permanent blocks, while the concentration of CO2 and its reduced changes was in the treatment of natural roots (A1) both in Blocks B1 and B2.

Simulating and modeling CO2 flux emitted from decomposed oil palm root cultivated at tropical peatland as affected by water content and residence time

Determining the oil palm dead roots contribution to total (R&lt;sub&gt;t&lt;/sub&gt;) and heterotrophic (R&lt;sub&gt;h&lt;/sub&gt;) respiration as a source of greenhouse gas/GHG emission in tropical peatland is urgently required, as well as predicting their magnitude to cope with difficulties of direct in-situ measurement. This study is designed to simulate the CO&lt;sub&gt;2&lt;/sub&gt; flux emitted from oil palm dead roots/R&lt;sub&gt;dr&lt;/sub&gt; in tropical peatland as affected by water content/WC and residence time/RT. The dead oil palm roots were cleaned, treated with control/15, 100, 150, 300, and 450%WC, and then incubated for three months. CO&lt;sub&gt;2&lt;/sub&gt; flux measurement, C, N, and CN ratio determination were conducted every month. This study demonstrated the importance R&lt;sub&gt;dr&lt;/sub&gt; among other CO&lt;sub&gt;2&lt;/sub&gt; emission sources, ranging from 0.05-2.3 Mg CO&lt;sub&gt;2&lt;/sub&gt; ha&lt;sup&gt;-1&lt;/sup&gt; year&lt;sup&gt;-1&lt;/sup&gt; with an average of 0.7 Mg CO&lt;sub&gt;2&lt;/sub&gt; ha&lt;sup&gt;-1&lt;/sup&gt; year&lt;sup&gt;-1&lt;/sup&gt;. R&lt;sub&gt;dr&lt;/sub&gt; contribution for literature R&lt;sub&gt;t&lt;/sub&gt; and R&lt;sub&gt;h&lt;/sub&gt; were around 0.3 to 1.3 and 0.9 to 3.5%, respectively. As a product of microbial respiration, R&lt;sub&gt;dr&lt;/sub&gt; was affected by WC and RT, supported by analysis of variance, linear mixed effect model/REML, and multivariate analysis. 100-150%WC resulting in significant and highest R&lt;sub&gt;dr&lt;/sub&gt;, whereas the increase (300-450%WC) or decrease (15%WC) would generate lower emission. R&lt;sub&gt;dr&lt;/sub&gt; culminated in the first month after incubation; meanwhile, it declined in the following months. This study also emphasized non-linear relationships between CO&lt;sub&gt;2&lt;/sub&gt; flux and other root properties, which can be modeled conveniently using non-linear approach, particularly using polynomial and artificial intelligence-based models. The simulation presented in this study served as an initial attempt to separate R&lt;sub&gt;dr&lt;/sub&gt; from R&lt;sub&gt;h&lt;/sub&gt;, as well as to predict CO&lt;sub&gt;2&lt;/sub&gt; flux with reasonable accuracy and interpretable methods.

ROOT DISTRIBUTION OF MATURE OIL PALMS IN MINERAL AND PEAT SOILS AND ITS IMPLICATION ON FERTILISER PLACEMENT

The correct placement of fertilisers is critical, as losses can be very significant especially in regions of high and frequent rainfall, non-terraced slopes, sandy textured soils and peat. To maximise uptake efficiency, fertilisers should be evenly broadcast over the soil surface area that contains the highest density of feeder roots. In order to determine the latter, an investigation was undertaken to ascertain the biomass and distribution of roots of various ages of mature oil palms planted in both mineral and second generation peat soils. Results of the study indicate that if site factors are not limiting, palm age and past fertiliser placement history are two major factors influencing oil palm root development and distribution. In mature well decomposed peat, although roots could be found growing 4 m from palm bole, actual root biomass per unit volume of soil was low. Only 21 per cent of the feeder roots of 8-year-old palms were found growing outside the weeded palm circles (WPC). Even within the latter, approximately 50 per cent were concentrated within a radius of 1 m from the palm bole. The low bulk density and high porosity of peat appears to discourage roots from growing beyond this distance. In mineral soils, there was a consistent and gradual increase in root spread beyond the WPC, with palm age. Feeder root distribution beyond a 2 m radius ranged from as low as 26 per cent in 6-year-old palms planted on terraces to 41 per cent for 8-year-old palms established in non-terraced soils. Only palms older than 10 years of age had root biomass greater than 50 per cent beyond this radius. In all sites, there was an increase in primary and secondary root biomass with soil depth and a linear decrease in feeder root biomass down the soil profile. Soil chemical analysis indicated that apart from palm age, the horizontal and vertical distribution of feeder roots was strongly influenced by soil fertility gradients created by past fertiliser placement history. As fertilisers were previously applied entirely in the WPC for younger palms (&lt;8 years), there was a significant decline in soil fertility with increasing distance from the palm bole and increasing soil depth. The majority of feeder roots were concentrated within the 2 m radius from the palm bole and in the top 20 cm of soil, where nutrient levels were the highest. In older palms (&gt;10 years) where fertilisers had been broadcast over frond heaps in the interpalm spaces and interrows, feeder root biomass was higher outside the WPC, as soil fertility gradients were less apparent. Taking into account the root distribution patterns of oil palm in relation to palm age, specific recommendations on fertiliser placement for oil palm grown on mineral and peat soils are made, so as to improve fertiliser uptake and utilisation.

Defense response changes in roots of oil palm (Elaeis guineensis Jacq.) seedlings after internal symptoms of Ganoderma boninense Pat. infection

BackgroundThe development of basal stem rot (BSR) disease in oil palm is associated with lignin during vegetative growth and salicylic acid (SA) biosynthesis. The increase in the lignin content, SA accumulation, growth, and root biomass could indicate the resistance of oil palm seedlings to BSR disease. Therefore, although there are many studies on the interactions between the Ganoderma boninense and oil palm, research on evaluation of physiological processes, biochemistry, and molecules occurring during early internal symptoms of BSR in roots of oil palm (Elaeis guineensis Jacq.) are essential.ResultsGanoderma boninense inoculation indicated that C01, C02, and C05 seedlings were susceptible, while the other three seedlings, C03, C07, and C08, were resistant based on Ganoderma Disease Index (GDI). Infection by G. boninense in the most susceptible seedlings C05 reduced fresh weight of roots (FW) by 9.0%, and lignin content by 10.9%. The most resistant seedlings C08 were reduced by only 8.4%, and 0.2% regarding their fresh weight and lignin content, respectively. BSR disease induced SA accumulation in the most susceptible C08 and decreased peroxidase (PRX) enzyme (EC 1.11.1.7) activities in root tissues of oil palm seedlings except C07 and C08 where PRX activities remained high in the 4 months after planting. Infection with G. boninense also increased glutathione S-transferase U19-like (EgGSTU19) gene expression in the root tissues of susceptible seedlings, while laccase-24 (EgLCC24) gene expression was associated with resistance against BSR disease. Based on the relative expression of twelve genes, two genes are categorized as receptors (EgWAKL5, EgMIK1), two genes as biosynthesis signal transduction compound (EgOPR5, EgACO1), five genes as defense responses (EgROMT, EgSOT12, EgLCC24, EgGLT3, EgGSTU19), and one gene as trans-resveratrol di-O-methyltransferase-like (EgRNaseIII) predicted related to BSR infection. While two other genes remain unknown (EgUnk1, EgUnk2).ConclusionsGanoderma infection-induced SA accumulation and lignification in resistant accessions promote the seedlings root biomass. Oil palm seedlings have a synergistic physical, biochemical, and molecular defense mechanism to the BSR disease. The utilization of nucleotide-based molecular markers using EgLCC24 gene is able to detect resistant oil palm seedlings to G. boninense.