Sariah Meon

Efficiency of plant growth-promoting rhizobacteria (PGPR) for the enhancement of rice growth.

Plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria that colonize plant roots and enhance plant growth by a wide variety of mechanisms. The use of PGPR is steadily increasing in agriculture and offers an attractive way to replace chemical fertilizers, pesticides, and supplements. Here, we have isolated and characterized the PGPR from the rhizosphere soil of rice field for the enhancement of growth of rice. Rhizosphere soils were collected from different areas of Mymensingh in Bangladesh. Ten isolates of bacteria, designated as PGB1, PGB2, PGB3, PGB4, PGB5, PGT1, PGT2, PGT3, PGG1 and PGG2, were successfully isolated and characterized. Subsequently, to investigate the effects of PGPR isolates on the growth of rice, a pot culture experiment was conducted. Prior to seeds grown in plastic pots, seeds were treated with PGPR isolates and seedlings were harvested after 21 days of inoculation. Isolates PGB4, PGT1, PGT2, PGT3, PGG1 and PGG2 induced the production of indole acetic acid (IAA), whereas only PGT3 isolate was able to solubilize phosphorus. Most of isolates resulted in a significant increase in plant height, root length, and dry matter production of shoot and root of rice seedlings. Furthermore, PGPR isolates remarkably increased seed germination of rice. Among the ten isolates, PGB4 and PGG2 were found almost equally better in all aspects such as dry matter production, plant height and root length of rice, and IAA production. Isolate PGT3 was also found to be promising in IAA production having an additional property of phosphate solubilization. The present study, therefore, suggests that the use of PGPR isolates PGB4, PGG2 and PGT3 as inoculant biofertilizers might be beneficial for rice cultivation as they enhanced growth of rice, and induced IAA production and phosphorus solubilization.

Isolation and characterization of phosphate-solubilizing bacteria from aerobic rice

Phosphate-solubilizing bacteria are frequently used as plant growth promoters. A study was conducted to isolate phosphate-solubilizing bacteria (PSB) from aerobic rice grown in Penang Malaysia and to determine some biochemical properties of the isolates such as, organic acids, enzymes, indoleacetic acid (IAA), siderophore production and its antagonistic effect against pathogen Rhizoctonia solani. Selective media used for the isolation were; Pseudomonas aeruginosa (PA), national botanical research institutes phosphate growth medium (NBRIP), Pikovskaya and Pseudomonas spp. (PS). Organic acid production was determined using high performance liquid chromatography (HPLC). The PSB populations were higher in rhizosphere than non-rhizospheric soil and the highest population was found in PS and Pikovskaya, while the lowest was found in PA media plates. The highest P solubilizing activity (69.58%) was found in PSB9 strain grown in NBRIP plate. Isolated PSB were able to produce different organic acids and growth hormone such as IAA. A number of PSB isolates belong to the Bacillus sp. and proved for the antagonistic effect against R. solani (sheath blight) even though most of the isolated strains can grow in nitrogen, free semi-solid medium and able to produce siderophore. PSB inoculants with their beneficial traits would be considered as potential biofertilizer for the sustainable aerobic rice cultivation system.

Induction of tolerance to Fusarium wilt and defense-related mechanisms in the plantlets of susceptible Berangan banana pre-inoculated with Pseudomonas sp. (UPMP3) and Burkholderia sp. (UPMB3).

This study is aimed at assessing the ability of two endophytic bacteria originally isolated from healthy oil palm roots, Pseudomonas sp. (UPMP3) and Burkholderia sp. (UPMB3) to induce resistance in susceptible Berangan banana against Fusarium oxysporum race 4 (FocR4). Increased accumulation of resistance-related enzymes such as peroxidase (PO), phenylalanine ammonia lyase (PAL), lignithioglycolic acid (LTGA), and pathogenesis-related (PR) proteins (chitinase and β-1,3-glucanase) has been observed in plantlets treated with endophytic bacteria UPMP3 and UPMB3 singly or as mixture under glasshouse conditions. Pre-inoculation of banana plantlets with UPMP3 showed a significant reduction in Fusarium wilt incidence 72 d after challenged inoculation with FocR4. UPMB3 was less effective in suppressing Fusarium wilt compared to UPMP3, whereas, the mixture of both endophytes showed an intermediate effect. Based on these results, it is concluded that UPMP3 could be a promising biological control agent that can trigger resistance against Fusarium wilt in susceptible Berangan banana.

Sequence analysis and gene expression of putative exo- and endo-glucanases from oil palm (Elaeis guineensis) during fungal infection.

Glucanases are enzymes that hydrolyze a variety β-d-glucosidic linkages. Plant β-1,3-glucanases are able to degrade fungal cell walls; and promote the release of cell-wall derived fungal elicitors. In this study, three full-length cDNA sequences encoding oil palm (Elaeis guineensis) glucanases were analyzed. Sequence analyses of the cDNA sequences suggested that EgGlc1-1 is a putative β-d-glucan exohydolase belonging to glycosyl hydrolase (GH) family 3 while EgGlc5-1 and EgGlc5-2 are putative glucan endo-1,3-β-glucosidases belonging to GH family 17. The transcript abundance of these genes in the roots and leaves of oil palm seedlings treated with Ganoderma boninense and Trichoderma harzianum was profiled to investigate the involvement of these glucanases in oil palm during fungal infection. The gene expression of EgGlc1-1 in the root of oil palm seedlings was increased by T. harzianum but suppressed by G. boninense; while the gene expression of both EgGlc5-1 and EgGlc5-2 in the roots of oil palm seedlings was suppressed by G. boninense or/and T. harzianum.

Symbiotic interaction of endophytic bacteria with arbuscular mycorrhizal fungi and its antagonistic effect on Ganoderma boninense.

Endophytic bacteria (Pseudomonas aeruginosa UPMP3 and Burkholderia cepacia UMPB3), isolated from within roots of oil palm (Elaeis guineensis Jacq.) were tested for their presymbiotic effects on two arbuscular mcorrhizal fungi, Glomus intraradices UT126 and Glomus clarum BR152B). These endophytic bacteria were also tested for antagonistic effects on Ganoderma boninense PER 71, a white wood rot fungal pathogen that causes a serious disease in oil palm. Spore germination and hyphal length of each arbuscular mycorrhizal fungal (AMF) pairing with endophytic bacteria was found to be significantly higher than spores plated in the absence of bacteria. Scanning electron microscopy (SEM) showed that the endophytic bacteria were scattered, resting or embedded on the surface hyaline layer or on the degraded walls of AMF spores, possibly feeding on the outer hyaline spore wall. The antagonistic effect of the endophytic bacteria was expressed as severe morphological abnormalities in the hyphal structures of G. boninense PER 71. The effects of the endophytic bacteria on G. boninense PER 71 hyphal structures were observed clearly under SEM. Severe inter-twisting, distortion, lysis and shriveling of the hyphal structures were observed. This study found that the effect of endophytic bacteria on G. intraradices UT126 and G. clarum BR152B resembled that of a mycorrhiza helper bacteria (MHB) association because the association significantly promoted AMF spore germination and hyphal length. However, the endophytic bacteria were extremely damaging to G. boninense PER 71.

Early detection of basal stem rot disease Ganoderma in oil palms based on hyperspectral reflectance data using pattern recognition algorithms

Basal stem rot (BSR) is a fatal fungal (Ganoderma) disease of oil palm plantations and has a significant impact on the production of palm oil in Malaysia. Because there is no effective treatment to control this disease, early detection of BSR is vital for sustainable disease management. The limitations of visual detection have led to an interest in the development of spectroscopically based detection techniques for rapid diagnosis of this disease. The aim of this work was to develop a procedure for early and accurate detection and differentiation of Ganoderma disease with different severities, based on spectral analysis and statistical models. Reflectance spectroscopy analysis ranging from the visible to near infrared region (325–1075 nm) was applied to analyse oil palm leaf samples of 47 healthy (G0), 55 slightly damaged (G1), 48 moderately damaged (G2), and 40 heavily damaged (G3) trees in order to detect and quantify Ganoderma disease at different levels of severity. Reflectance spectra were pre-processed, and principal component analysis (PCA) was performed on different pre-processed datasets including the raw dataset, first derivative, and second derivative datasets. The classification models: linear and quadratic discrimination analysis, k-nearest neighbour (kNN), and Naïve–Bayes were applied to PC scores for classifying four levels of stress in BSR-infected oil palm trees. The analysis showed that the kNN-based model predicted the disease with a high average overall classification accuracy of 97% with the second derivative dataset. Results confirmed the usefulness and efficiency of the spectrally based classification approach in rapid screening of BSR in oil palm.

Preparation, characterisation and viability of encapsulated Trichoderma harzianum UPM40 in alginate-montmorillonite clay

Microencapsulation is a process by which tiny parcels of an active ingredient are packaged within a second material for the purpose of shielding the active ingredient from the surrounding environment. This study aims to determine the ability of the microencapsulation technique to improve the viability of Trichoderma harzianum UPM40 originally isolated from healthy groundnut roots as effective biological control agents (BCAs). Alginate was used as the carrier for controlled release, and montmorillonite clay (MMT) served as the filler. The encapsulated Ca-alginate-MMT beads were characterised using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The FTIR results showed the interaction between the functional groups of alginate and MMT in the Ca-alginate-MMT beads. Peaks at 1595, 1420 and 1020 cm−1 characterised alginate, and peaks at 1028 and 453 cm−1 characterised MMT; both sets of peaks appeared in the Ca-alginate-MMT FTIR spectrum. The TGA analysis showed an improvement in the thermal stability of the Ca-alginate-MMT beads compared with the alginate beads alone. SEM analysis revealed a homogeneous distribution of the MMT particles throughout the alginate matrix. T. harzianum UPM40 was successfully encapsulated in the Ca-alginate-MMT beads. Storage analysis of the encapsulated T. harzianum UPM40 showed that the low storage temperature of 5°C resulted in significantly (p < 0.05) better storage compared with room temperature (30°C).

Effect of seed bacterization on plant growth response and induction of disease resistance in chilli.

This study aimed to examine the induction of disease resistance, and growth response in chilli plants elicited by plant growth promoting endophytic bacteria [Pseudomonas aeruginosa (UPMP3), Burkholderia cepacia (UPMB3), and Serratia marcescens (UPMS3)]. Seed bacterization with UPMP3 and UPMB3 significantly increased peroxidase (PO), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) activities. This increase corresponded to greater reduction in pre- and post-emergence damping-off caused by Sclerotium rolfsii. UPMS3 alone or as mixture with UPMP3 and UPMB3 did not show any significant reduction in disease incidence. However, all the isolates tested did not inhibit the seed germination and seedling establishment in chilli.

Induction of host defence enzymes by the endophytic bacterium Serratia marcescens, in banana plantlets.

Pre-inoculation with the endobacterium Serratia marcescens (strain UPM39B3) induced the production of host defence enzymes such as peroxidase, polyphenoloxidase, phenylalanine ammonia lyase, total soluble phenols and lignothioglycolic acid in banana plantlets. The levels of these enzymes were evidently higher in plantlets pre-treated with the endobacterium compared to the control. The production of host-induced enzymes benefitted the crop plants as they may have a role in suppressing Fusarium wilt incidence in the plantlets. This was evident when plantlets pre-treated with the endobacterium showed a lower disease severity (50%) compared to diseased plantlets lacking the endobacterium (74%). The results of this study thus highlight the potential of the isolate Serratia marcescens (strain UPM 39B3) as a biological control agent for Fusarium wilt management in bananas, reducing disease severity via stimulation of host defences.

Cloning of nitric oxide associated 1 (NOA1) transcript from oil palm (Elaeis guineensis) and its expression during Ganoderma infection.

Nitric oxide associated 1 (NOA1) protein is implicated in plant disease resistance and nitric oxide (NO) biosynthesis. A full-length cDNA encoding of NOA1 protein from oil palm (Elaeis guineensis) was isolated and designated as EgNOA1. Sequence analysis suggested that EgNOA1 was a circular permutated GTPase with high similarity to the bacterial YqeH protein of the YawG/YlqF family. The gene expression of EgNOA1 and NO production in oil palm root tissues treated with Ganoderma boninense, the causal agent of basal stem rot (BSR) disease were profiled to investigate the involvement of EgNOA1 during fungal infection and association with NO biosynthesis. Real-time PCR (qPCR) analysis revealed that the transcript abundance of EgNOA1 in root tissues was increased by G. boninense treatment. NO burst in Ganoderma-treated root tissue was detected using Griess reagent, in advance of the up-regulation of the EgNOA1 transcript. This indicates that NO production was independent of EgNOA1. However, the induced expression of EgNOA1 in Ganoderma-treated root tissues implies that it might be involved in plant defense responses against pathogen infection.