Faculty of Biological Sciences

Soil carbon pools and dynamics in the Sal forests of Bangladesh

2026-04-20T04:30:16Z

Soil carbon pools and dynamics in the Sal forests of Bangladesh RAHMAN, MD. HABIBUR Carbon (C) concentrations in different Sal forests of Bangladesh have not yet been estimated to explore their C storage potential. The present study compared the C pools among three selected Sal forests located in Madhupur, Lalmai and Singra to examine the effect of management intensity on C stocks. A total of 19 plots (each 10 m × 10 m for tree, 5 m × 5 m for shrubs and 0.5 m × 0.5m for herbs in size), 9 from Madhupur forest and each 5 from the other two forests, were established to collect data on plant composition, plant DBH and organic C concentrations. Allometric method was used to estimate C concentrations for both aboveground and belowground parts of juvenile and adult tree plants of the selected plots. Wood biomass was converted to C content by multiplying the value with the van Bemelen factor (1.724). Litter biomass C, soil organic C and fine root C were determined during winter (December) and summer (May) of 2016. Seasonal variation in culturable soil bacterial colony counts was also studied in three replicated plots selected from Madhupur Sal forest. The results showed that woody C concentration was significantly (p = 0.0156) higher in Lalmai (552.46±64.09 t/ha) and Singra forests (547.13±62.43 t/ha) than in Madhupur Sal forest (354.03±38.43 t/ha). The mean DBH of Sal tree at breast height was significantly (p = 0.022) higher in Lalmai (38.84±2.12 cm) and Singra (37.36±1.97 cm) forests than in Madhupur forest (30.72±1.93 cm). On the other hand, fine root C and soil C were determined at three different depths: 0-10 cm, 10-20 cm and 20-30 cm. The litter and fine root dry biomass were converted to C content and expressed as tonnes C per hectare area. Soil C content was calculated using the bulk density method. The decomposition of Sal leaf litter and seasonal changes in bacterial communities were studied to explain the observed temporal changes in biomass C content in the study area. The decomposition rate (mass loss and N mineralization rate) of Sal leaf litter was studied by incubating leaf litter with soil collected from three selected Sal forests following a reciprocal experimental design where each Sal leaf litter was incubated with soil collected from three Sal forests. The number of bacterial colonies was compared in summer, monsoon, late autumn and winter seasons in a plot of Madhupur Sal forest. Litter biomass C was significantly higher in May compared to December, although the effect of forest was not significant. Fine root biomass C was significantly affected by forest type (p < 0.0001) and depth (p < 0.0001) where the maximum amount was found in Madhupur sal forest and the lowest in Lalmai Sal forest and 0-10 cm depth showed the highest value among the three selected Sal forests. Soil C content was significantly affected by both forest type (p < 0.0001) and depth (p < 0.05) where the value was higher in Singra National Park, followed by Madhupur Sal forest and Lalmai Sal forest, however, the highest value was recorded at 10 cm depth, followed by 20 cm and 30 cm depth. Nitrogen mineralization rate was significantly affected by soil type and the mean value was higher in Lalmai Sal forest. For fast-growing bacteria, the number of small- sized colonies was higher in late autumn but lower in winter, while the number of large-sized colonies was higher in winter but lower in late autumn. For slow-growing bacteria, the number of smallsized colonies was higher in late autumn but lower in winter, while the number of large-sized colonies was higher in winter but lower in late autumn. This study suggests that long-term forest conservation may be an effective method for increasing C stocks in forest ecosystems. Result also suggest to consider assessment of C stocks of temporal scale for more accurate estimation of C dynamics. This thesis is submitted for the degree of Doctor of Philosophy.

Identification and characterization of genes from wild halophytic rice (Porteresia coarctata), for using in development of salt tolerant rice

2026-04-19T06:25:48Z

Identification and characterization of genes from wild halophytic rice (Porteresia coarctata), for using in development of salt tolerant rice Habiba, Most Umme Soil salinity is a major abiotic constraint affecting rice cultivation in coastal and estuarine regions, where rising sea levels and irrigation-induced salinization increasingly threaten global food security. The halophytic wild rice species Oryza coarctata—the only naturally salt-tolerant species in the genus Oryza, which can set rice-like grains—offers a promising genetic reservoir for improving salt stress tolerance in cultivated rice (Oryza sativa). This study presents a comprehensive functional and molecular characterization of O. coarctata, along with its application in wide hybridization and genetic engineering strategies aimed at enhancing salt tolerance in rice. Oryza coarctata exhibits exceptional salt tolerance supported by unique physiological and anatomical features. Its leaf structure includes deep adaxial invaginations, multiple vascular bundles per ridge, and salt-secreting hairs, while its roots possess a thickened exodermis, large xylem vessel, and well-developed aerenchyma—traits that aid in ionic regulation and survival in saline, waterlogged conditions. Notably, O. coarctata reduced electrical conductivity (EC) of saline hydroponic media by 2.77–8.51 dS/m across 100–300 mM NaCl, demonstrating a desalination ability absent in salt-sensitive rice varieties. Co-cultivation of O. coarctata with BRRI Dhan28 improved the latter’s growth and yield under 100 mM salt stress, increasing yields from 34% to 67%. Gas exchange measurements in O. coarctata showed only modest declines in photosynthesis at 100–300 mM NaCl (14–26% reduction in CO₂ assimilation), with strong light response (r = 0.932) and moderate Jₘₐₓ reduction (19–32%, p < 0.05). Unlike O. sativa, which fails at 80 mM salt, O. coarctata maintains high photosynthetic efficiency and survival under extreme salinity. These traits underscore its potential for use in salt-affected rice ecosystems through ecological facilitation and genetic improvement strategies. To explore gene transfer from the tetraploid O. coarctata (4n=2x=48) into rice, a wide hybridization approach was adopted using a tetraploid O. sativa (var. Latisail 4n) as the maternal parent. This approach is referred to as the bulbosum technique, where chromosomal loss occurs resulting in half of the original chromosomes (2x). Despite high genomic divergence, two partial 18 hybrids were recovered out of 1,191 pollinated spikelets, indicating successful albeit low-frequency gene introgression. These partial hybrids exhibited intermediate phenotypes, including fibrous and tap root systems, variable seed morphology, and in some cases, the absence of leaf midribs—a signature trait of O. coarctata. Molecular analysis confirmed that the hybrids carried specific chromosomal segments from O. coarctata, particularly on chromosomes 3 and 12. Partial hybrid lines A2-06-01, A2-10-01, and B2-03-01 exhibited significantly higher chlorophyll content than diploid and tetraploid O. sativa following 100 mM salt stress. Lines B-02-01 and B-03-01 showed significantly greater plant height compared to O. sativa (2n), while A2-06-01 and A2-10-01 also demonstrated a significantly higher tiller number than O. sativa (2n). A significant advancement of this work was the development of O. coarctata-specific SSR markers to facilitate molecular screening of hybrids lines. Initially, known SSR markers from the Gramene database showed limited polymorphism between O. sativa and O. coarctata. Subsequently, 90 markers from the O. officinalis genome (CC genome), developed under the OMAP project, were tested. Of these, 19 markers were optimized to uniquely detect O. coarctata alleles across most chromosomes (except 5 and 8). In addition, seven new SSR markers were developed from O. coarctata genomic sequences. These 26 markers together form a robust toolkit for identifying and validating introgressions in future breeding programs. To directly assess the functional contribution of O. coarctata genes, three candidate genes—OcAsr1 (abscisic acid stress ripening protein), OcPVA1 (vacuolar H⁺-ATPase subunit c), and OcMT3 (metallothionein type 3)—were cloned and overexpressed in O. sativa using in planta Agrobacterium-mediated transformation method. This non-tissue culture-based transformation system enabled the successful generation of transgenic lines in the high-yielding indica background BRRI Dhan75 (for OcAsr1and OcPVA1) and BRRI Dhan67 (for OcMT3). Gene expression profiling revealed distinct stress-inducible expression patterns of the genes in O. coarctata: OcAsr1 peaked at 24 hours under 200 mM NaCl, OcPVA1 showed strong and consistent expression across both 100 and 200 mM NaCl, and OcMT3 exhibited a late response, peaking at 48 hours. Transgenic lines overexpressing OcAsr1 (notably P_73_2, P_70_1, and P_76_2) displayed enhanced root and shoot biomass, chlorophyll retention, and a 30–50% reduction in root and shoot Na⁺/K⁺ ratios. These lines maintained 40–50% higher grain yield under 100 mM NaCl 19 and exhibited minimal yield penalty under normal conditions. OcPVA1-expressing lines (MUH_113, MUH_117, MUH_99) demonstrated strong early responses, enhanced membrane stability, improved ionic balance, and significant grain yield retention under salinity. These results support its role in ion transport and vacuolar compartmentalization of sodium ions. Transgenic lines expressing OcMT3 (P-14-1, P-13-2) showed reduced oxidative damage (as measured by electrolyte leakage and histochemical staining), improved Na⁺/K⁺ balance, and stable yield under stress, highlighting OcMT3's role in ROS detoxification and metal ion sequestration. Importantly, all three gene constructs did not compromise yield under non-saline conditions, underscoring their suitability for future breeding or biotechnological applications. This study highlights the remarkable salt tolerance of Oryza coarctata and its potential to enhance salinity resilience in cultivated rice through wide hybridization and genetic engineering. Functional traits, molecular markers, and transgenic lines expressing O. coarctata genes demonstrated improved growth, yield, and stress tolerance under saline conditions, offering promising avenues for climate-resilient rice breeding. This thesis is submitted for the degree of Doctor of Philosophy.

Insecticidal activity of indigenous Bacillus thuringiensis strains against Tephritids fruit fly pests affecting fruits and vegetables

2026-04-19T04:03:28Z

Insecticidal activity of indigenous Bacillus thuringiensis strains against Tephritids fruit fly pests affecting fruits and vegetables Bari, Md. Abdul The extensive and indiscriminate use of synthetic chemical insecticides in agriculture and forestry has led to several unintended and detrimental consequences, including environmental pollution, the development of pest resistance, the mortality of non-target organisms, and negative public health effects. These challenges are particularly pronounced in developing countries like Bangladesh, where pest infestations significantly reduce crop productivity and economic gains. As a sustainable and environmentally safer alternative, microbial biopesticides, particularly those derived from Bacillus thuringiensis (Bt), have emerged as a promising solution. Bt-based biopesticides are host-specific, biodegradable, and effective, offering significant potential to reduce chemical pesticide dependency. This study aimed to evaluate insecticidal activity of previously isolated, characterized and preserved indigenous Bacillus thuringiensis (Bt) strains from different eco-regions of Bangladesh against four economically important Tephritid fruit fly pests, Bactrocera dorsalis, B. zonata, Zeugodacus cucurbitae and Z. tau. These pests are known to cause extensive damage to fruits and vegetables, impacting local consumption, export opportunities, and national food security. A total of 44 Bt strains were isolated, identified, and screened through a comprehensive suite of phenotypic, genetic, proteomic, and toxicity analyses. The overarching goal was to identify highly potent Bt strains and validate their effectiveness under both laboratory and field conditions. Initial screening of the 44 native Bt isolates showed that 16 strains could induce greater than 50% and three potential strains JSd1, SaS6, and JDc1 exceeded 80% larval mortality in all four Tephritid species tested. Bt strain JSd1 consistently demonstrated the highest efficacy, inducing 97% mortality in B. dorsalis, 95% in B. zonata, 95% in Z. cucurbitae, and 92% in Z. tau, outperforming even the reference Btk HD-73 and Bts T84A1. Further toxicological analyses, including lethal concentrations (LC₅₀) and lethal time (LT₅₀) values, confirmed JSd1’s superior performance. LC₅₀ values ranged from 0.431 to 0.472 mg/ml and LT₅₀ values ranged between 54.09 and 55.17 hours, which are significantly lower than other strains, indicating high potency at reduced concentrations, while faster action and quicker pest knockdown. Beyond bioassays, the study also evaluated the biological quality parameters of insects exposed to Bt treatment infested with preferred hosts, which are critical in understanding sub-lethal effects and potential population suppression in pest communities. Bt JSd1, SaS6, and JDc1 significantly reduced pupal yield, pupal weight, adult emergence percentage, and flying ability iii across all four Tephritid species. For instance, Bt JSd1-treated groups consistently demonstrated the lowest pupal yield (as low as 99 ± 2.081 in Z. tau), lowest pupal weight (~8 mg), and lowest adult emergence (ranging from 39–53%). Emergence of malformed or half-emerged adults was also significantly higher in treated groups, while sex ratio distortion was minimal, suggesting that these strains primarily impacted general viability rather than sex-linked mortality. These results indicate a substantial decline in the reproductive and survival potential of these pest populations upon exposure to Bt biopesticides, making them highly effective components in Integrated Pest Management (IPM) strategies. To understand the genetic basis of its high efficacy, whole genome sequencing of Bt JSd1 was conducted. Genomic analysis revealed the presence of multiple Cry and Vip insecticidal genes, notably Cry22A and Vip3A, which are known for their effectiveness against Dipteran insects. Additionally, several virulence factors and biosynthetic gene clusters associated with secondary metabolite production were identified, contributing to the strain’s broad-spectrum insecticidal capability and environmental adaptability. This genetic richness further reinforces the potential of Bt JSd1 as a candidate for next-generation bioinsecticide development. Finally, field validation was carried out using the formulated Bt biopesticide (compared with chemical pesticides) on Solanum melongena (brinjal), a crop heavily impacted by the Eggplant Fruit and Shoot Borer (EFSB. Four-time foliar applications (Each of 100 ml volume containing 25.7 mg spore crystal mixture) of the Bt preparation reduced EFSB infestation to just 10%, compared to significantly higher levels in untreated controls, with no significant difference with the chemical pesticide. The average yield per plant increased from 1.45 kg (control) to 3.85 kg in the treated group, effectively matching or surpassing yields from chemically treated plots. Importantly, there were no observed negative impacts on beneficial insect populations or surrounding flora, highlighting the ecological safety of the product. Overall, this study provides compelling evidence for the viability and impact of indigenous Bt strains, particularly JSd1, as potent, safe, and affordable biocontrol agents, offering a sustainable solution to the challenges of chemical pesticide overuse, contributing to improved agricultural productivity, ecological health, and food security. Their local origin also enables domestic production and reduces reliance on imported formulations, supporting national bioeconomy goals. This thesis is submitted for the degree of Doctor of Philosophy.

High Density Lipoprotein in Bangladeshi Adults: Characterization and the Basis of its Variation

2026-03-02T04:46:36Z

High Density Lipoprotein in Bangladeshi Adults: Characterization and the Basis of its Variation Saiedullah, Muhammad Background and objectives: High-density lipoprotein cholesterol (HDL-c) constitutes a vital cardioprotective factor, yet low levels are prevalent among the Bangladeshi population, and its biochemical and genetic determinants remain poorly characterized. This study aimed to determine the prevalence of low HDL-c and associated components of dyslipidemia, along with their demographic and biochemical factors, among healthy Bangladeshi adults. The main focus of the study was to determine the effect of twelve single nucleotide polymorphisms (SNPs) in genes involved in lipid dynamics, i.e., ApoA1 (–75 G/A and +83 C/T), ApoB (7673C/T [rs693], 10108A/G [rs1801701], 12669G/A [rs1042031]), ABCA1 (–565C/T, 1051G/A, 2868G/A), PON1 (163T/A [rs854560, L55M] and 575A/G [rs662, Q192R]), and CETP (–629C/A, 277C/T [Taq1B]) was explored. Methodology: This cross-sectional study recruited 409 healthy adults from different areas of the Dhaka division. Participants were free from diabetes, hypertension, kidney, liver, or other chronic diseases. After obtaining informed consent, demographic measurements and clinical histories were recorded. Fasting blood samples (5 mL) were collected following aseptic procedures and processed for biochemical analyses using automated spectrophotometric instruments. Measurements of serum lipids, specifically total cholesterol (TC), triglycerides (TG), and HDL-c, were conducted by spectrophotometric end-point methods. Low-density lipoprotein cholesterol (LDL-c) was subsequently derived via the Friedewald formula. Additionally, Apolipoprotein A1 (ApoA1) and Apolipoprotein B (ApoB) concentrations in serum were quantified using immunoturbidimetry on an automated platform. A column-based genomic DNA extraction kit was used to extract DNA from homogenized whole blood leukocytes, and genotyped SNPs in the ApoA1, ApoB, ABCA1, PON1, and CETP genes using Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) followed by agarose-gel electrophoresis. We categorized the participants based on median HDL-c levels or according to reference values into lower HDL-c and higher HDL-c groups following NCEPATPIII guidelines for statistical analysis. Logistic or multiple linear regressions and Fisher’s exact tests were employed to assess associations between genotypes, allele frequencies, lipid profiles, and demographic variables. Results: The median value of serum HDL-c of the total participants was 34.0 (95%CI: 33.0– 35.0) mg/dL. Females exhibited significantly higher levels of HDL-c than males [37.1 (35.5– xvii 38.5) mg/dL vs. 31.6 (30.7–32.6) mg/dL, p < 0.001]. Lower levels of HDL-c (< 40 mg/dL for males and < 50 mg/dL for females) were prevalent in 91.9% of the participants with similar prevalence across genders (90.4% vs 93.7%, p = 0.229). Among the participants, elevated levels of triglycerides (>150 mg/dL) were found in 34.0%, total cholesterol (>200 mg/dL) in 21.0%, and LDL-c (>130 mg/dL) in 8.8%. In contrast to HDL-c, gender-based differences were observed in the prevalence of other lipid abnormalities. Elevated TG levels were significantly more common among males (40.2%) than females (26.8%, p = 0.005). Conversely, females exhibited a higher prevalence of elevated LDL-c (12.6% vs 5.5%, p = 0.013) and increased ApoA1 concentrations (62.6% vs 50.2%, p = 0.012). Their concentrations were also differed between genders, males with HDL-c below the median (< 31.6 mg/dL) showed higher TG (156 vs 114 mg/dL, p < 0.001) and BMI (24.65 vs 23.05 kg/m², p = 0.002) with lower ApoA1 (108 vs 132 mg/dL, p < 0.001), whereas females with lower levels of serum HDL-c (< 37.1 mg/dL) had lower levels of serum TC (159 vs 178 mg/dL, p < 0.001), LDL-c (102 vs 114 mg/dL, p < 0.001), and ApoA1 (123 vs 148 mg/dL, p < 0.001) along with higher TG (128 vs 103 mg/dL, p < 0.001). Logistic regression statistics identified increased TG and decreased ApoA1 as significant predictors of lower HDL-c across both genders. Across the gene loci studied, ApoA1 (–75 G/A and +83 C/T), ApoB (7673C/T, 10108A/G, 12669G/A), ABCA1 (–565C/T, 1051G/A, 2868G/A), PON1 (163T/A and 575A/G), and CETP (–629C/A and 277C/T), majority of the subjects exhibited wild-type homozygous genotypes. Heterozygous genotypes were less frequent than wild homozygous, and mutant homozygous genotypes were rare. The genotype distributions for most loci conformed to Hardy–Weinberg equilibrium (HWE). Exceptions were noted for ABCA1 2868G/A (p = 0.034), where the distribution deviated from HWE. We found no significant differences in HDL-c and ApoA1 or other lipid variables across the ApoA1 –75G/A and +83C/T genotypes among the overall subjects or males and females. In multivariable linear regression for HDL-c (n = 392), after adjusting for age, BMI, TG and LDL-c neither the –75GG (β = 0.806, p = 0.277) nor the +83CC (β = –1.212, p = 0.330) genotype showed any significant association with HDL-c in the overall sample. Within the male subgroup (n = 210), associations for –75GG (β = –0.665, p = 0.462) and +83CC (β = 1.535, p = 0.325) were non-significant. In contrast, in females the –75GG genotype was linked to a 2.78 mg/dL xviii increase (β = 2.783, p = 0.023) and the +83CC genotype to a 4.28 mg/dL decrease (β = –4.281, p = 0.031) in HDL-c. For serum ApoA1, the overall and male subgroup models showed no significant associations with either –75GG (overall: β = 0.629, p = 0.796; males: β = –2.401, p = 0.459, females: β = 4.606, p = 0.220 ) or +83CC (overall: β = –1.151, p = 0.778; males: β = 4.375, p = 0.434, females: β = –7.796, p = 0.201). Thus, ApoA1 –75 and +83 variants do not independently affect serum ApoA1 levels, they modulate HDL-c in a gender-specific manner, with significant associations observed only in females. Both the ApoB 12669G/A genotype distribution (p = 0.019) and allelic frequencies (p = 0.016) differed between normal and elevated LDL-c groups. Additionally, the ApoB 12669 A allele frequency was higher in subjects with elevated ApoB levels (p = 0.042). Logistic regression revealed the carriers of ApoB 10108 GA+AA had higher risk of elevated TG (OR = 3.36, 95% CI: 1.20–9.45, p = 0.021). Conversely, the ApoB 12669 GA+AA genotype was protective for elevated LDL-c (OR = 0.33, 95% CI: 0.12–0.87, p = 0.023) and elevated ApoB levels (OR = 0.51, 95% CI: 0.27–0.99, p = 0.045). None of the ABCA1 –565C/T, 1051G/A and 2868G/A SNPs differed in genotype distribution and allele frequency between the two groups of HDL-c (P>0.05). The ABCA1 –565TT, 1051AA, and 2868 GA+AA genotypes were not associated with low HDL-c. This was evident from the adjusted OR statistics: 0.80 (95% CI: 0.49 - 1.31, p = 0.186) for –565TT; 1.46 (95% CI: 0.74 - 2.89, p = 0.403) for 1051AA; and 1.12 (95% CI: 0.49 - 1.63, p = 0.809) for 2868 GA+AA. The median (95%CI) of the PON1 arylesterase (PON1-ARE) was 2.50 (2.41 – 2.56) kU/L in the total subjects and higher in males compared to females 2.56 (2.49 – 2.67) vs 2.41 (2.28 – 2.53, p = 0.028). PON1-ARE was highest in 163TT and 575GG genotypes, followed by heterozygous 163TA and 575AG, homozygous 163AA and 575AA. The 163TT, TA and TT genotypes and T, A alleles were almost similar in the two groups of HDL-c (p > 0.05). Similarly, the 575 AA, AG and GG genotypes and A, G alleles showed no difference between the two HDL-c groups (p >0.05). Logistic regression statistics revealed no association of 163T/A and 575A/G with HDL-c [OR(95%CI): 1.06 (0.68 – 1.65), p = 0.804; 0.90 (0.59 – 1.38), p = 0.630]. No significant differences in genotype distribution or allele frequencies of CETP –629CA and 277CT SNPs were observed between HDL-c groups (p > 0.05). For the 277C/T polymorphism, the combined 277(CC+CT) genotypes differed significantly from the TT genotype between HDL-c groups (p = 0.011, OR = 0.37, 95% xix CI = 0.18–0.78). Higher HDL-c was observed in –629AA (p = 0.023) and CA+AA (p = 0.043) carriers compared to CC carriers. Similarly, higher HDL-c was observed in 277TT (p = 0.002) and CT+TT (p = 0.019) carriers compared to CC genotype. Finally, multiple linear regression statistics revealed negative effects of -629CC (β = –1.106, p = 0.038) and 277(CC+CT) (β = – 0.963, p = 0.016) on serum HDL-c levels. Conclusion: Low levels of HDL-c are exceedingly prevalent among the Bangladeshi population and are associated with male gender, elevated TG and decreased ApoA1 levels, potentially contributing to a higher risk of atherosclerotic cardiovascular disease (ASCVD) in this group. The ApoA1 –75GG showed positive and +83CC showed a negative significant impact on HDL-c only in females. The ApoB 10108G/A polymorphism was associated with elevated TG, and the 12669G/A variant was linked to elevated LDL-c and ApoB levels, although ApoB gene polymorphisms did not affect serum HDL-c levels. No association was found between circulating HDL-c levels and the common ABCA1 genotypes –656CT (heterozygous), 1051GA (heterozygous), and 2868GG (wild homozygous). PON1 163T/A and 575A/G polymorphisms contributed to circulating PON1 esterase activity but were not associated with serum HDL-c. Notably, the CETP –629CC, 277CC, and 277CT genotypes were associated with low levels of HDL-c in the Bangladeshi population, suggesting that screening for CETP gene variants may serve as a valuable biomarker for diagnosing low HDL-c levels and potentially guiding interventions to reduce ASCVD risk in this population. This thesis is submitted for the degree of Doctor of Philosophy.