Eric-Olivier Tienebo

Foliar diseases constrain the production of healthy rubber tree planting material in humid tropical nurseries. We tested whether preventive and post-symptom fungicide programmes reduced cumulative foliar disease on Hevea brasiliensis clone IRCA 331 during one nursery season at Bongo, Côte d’Ivoire. The present study analysed two fungicide trials conducted in a rubber nursery at Bongo, southeastern Côte d’Ivoire. Every active programme reduced cumulative incidence relative to the untreated control (all Holm-adjusted P < 0.001): suppression was 75.3–94.1% in the preventive trial and 88.2–93.6% in the post-symptom trial. Severity on the older first leaf tier did not differ among treatments, whereas severity on newly emerged foliage declined by 60.2–88.9% and 86.4–91.9%, respectively (all Holm-adjusted P < 0.001). Treatment effects on cumulative incidence and new-foliage severity were large (partial eta-squared ≥ 0.864). Tukey-adjusted comparisons identified overlapping efficacy groups among many active programmes; therefore, the smallest numerical estimate did not establish a uniquely superior programme. Adding a spray adjuvant produced no consistent detectable improvement in cumulative disease control. These findings demonstrate strong disease suppression under the tested site, season, and clone, but do not establish broad recommendations or non-inferiority of lower-input programmes. Multi-season, multi-location trials with molecular pathogen confirmation, complete weather and application records, and prespecified agronomic margins are required before operational recommendations are generalised.

Background: Water deficit is a major constraint on maize growth, while the effects of arbuscular mycorrhizal fungi can vary with host genotype and experimental context. Aims: This study evaluated biomass stability and supporting physiological responses of B73, EV8728SR, and W438 under water deficit with or without Rhizophagus irregularis inoculation. Study Design: We compared B73, EV8728SR, and W438 in a genotype-complete assay at 100% and 10% soil water-holding capacity (WHC), with non-inoculated (NM) and AMF Rhizophagus irregularis (Ri) treatments, and independently evaluated B73 and EV8728SR across 100%, 50%, and 10% WHC. Place and Duration of Study: The experiments were conducted under controlled greenhouse conditions at Institut National Polytechnique Félix Houphouët-Boigny (INP-HB), Yamoussoukro, Côte d'Ivoire; the common assay ran from February to March 2024. Methodology: Total plant dry biomass was the primary endpoint. Positive outcomes were analysed with log-Gaussian factorial models and HC3 Type III tests; proportions were analysed using beta regression. Estimated marginal means were compared among all genotypes within each inoculation × water panel using Tukey adjustment, and biomass tolerance indices were estimated with 2,000 stratified bootstrap resamples. Results: In the common assay, biomass differed by genotype (F2,37 = 14.74, P < 0.0001) and water regime (F1,37 = 151.58, P < 0.0001), but not by genotype × water (P = 0.410) or genotype × inoculation × water (P = 0.614). EV8728SR had the greatest estimated severe-stress biomass (11.77 g NM; 15.16 g Ri) and the largest stress tolerance index under severe stress (STI; 0.523 NM; 0.659 Ri). In the independent gradient, however, B73 exceeded EV8728SR overall (F1,51 = 10.44, P = 0.0022), while water deficit remained the dominant effect (F2,51 = 43.23, P < 0.0001). Ion leakage showed a water-dependent three-way interaction (χ² = 12.05, P = 0.0024), whereas leaf area showed genotype × water and inoculation × water interactions after multiplicity control. Biomass provided no evidence of a general or genotype-specific Ri buffering effect. Conclusion: The contrasting genotype ranking between assays demonstrates that drought-tolerance claims should integrate absolute stress biomass, stability indices, and independent validation rather than relying on a single experiment or physiological proxy.

Arbuscular mycorrhizal fungi (AMF) can improve plant performance under drought, but responses depend on host genotype, fungal isolate, symbiosis duration, and stress intensity. We evaluated whether Rhizophagus irregularis DAOM 197198 mitigated short-term water deficit in the Ivorian plantain cultivar Affoto under greenhouse conditions. Plants were assigned to a 2 × 3 factorial combination of inoculation (non-mycorrhizal or R. irregularis) and water supply (100% or 50% substrate water-holding capacity [WHC] replenished daily, or water withheld) for 14 days after a 14-day establishment period. Growth, organ water content, electrolyte leakage, chlorophyll index, leaf temperature, functional leaves, root colonization, and substrate spore density were quantified. Positive continuous responses were analyzed using log-linear models and heteroscedasticity-robust Type III tests; bounded responses were analyzed using beta or quasibinomial models. Water supply strongly affected total dry biomass (F2,36 = 34.44, P < 0.001), whereas inoculation (P = 0.789) and the inoculation × water-supply interaction (P = 0.946) did not. Mean total dry biomass declined from 104.73 g at 100% WHC to 70.58 g at 50% WHC and 36.02 g when water was withheld. Mycorrhizal growth responses were 2.7%, -4.1%, and -0.4%, respectively, and all 95% bootstrap confidence intervals included zero. AMF mitigation ratios were 0.935 (95% CI 0.627-1.422) at 50% WHC and 0.970 (0.626-1.572) under water withholding. Microscopy confirmed hyphae, vesicles, and arbuscules in inoculated roots, and none in controls; arbuscular abundance across the root system ranged from 24.92% to 31.81%. Thus, fungal establishment occurred, but inoculation did not detectably alter drought-associated biomass loss. Water deficit also reduced tissue hydration, growth dimensions, SPAD, and functional leaf proportion while increasing electrolyte leakage and leaf temperature. For the tested cultivar-isolate combination, following a short establishment period and under severe combined soil-water and atmospheric stress, R. irregularis conferred no detectable mitigation of biomass.

Aims: To determine how maize genotype, Rhizophagus irregularis inoculum, and NaCl affect germination and seedling performance, while distinguishing inoculum effects before root colonisation from responses after mycorrhizal establishment.Study Design: A 2 × 2 × 3 factorial experiment compared B73 and EV8728SR, R. irregularis inoculum or a non-mycorrhizal control, and 0, 68, or 102 mM NaCl. Place and Duration of Study: The five-day germination assay and subsequent greenhouse experiment were conducted at the Institut National Polytechnique Félix Houphouët-Boigny, Yamoussoukro, Côte d’Ivoire. Methodology: The germination assay used three independent dishes per combination; most greenhouse endpoints used 11 independent pots per combination. Responses included final germination, mean germination time (MGT), germination speed index (GSI), biomass, morphology, chlorophyll, electrolyte leakage, tissue water content, and root colonisation. Endpoint-appropriate factorial models and Tukey-adjusted comparisons were applied. Results: Final germination was statistically uninformative. EV8728SR germinated faster than B73 (MGT and GSI, P < 0.001), and GSI declined with NaCl (P = 0.019). Total dry biomass showed effects of genotype (P < 0.001), inoculum (P = 0.007), and NaCl (P < 0.001), with no significant interactions. At 102 mM, the descriptive Ri-associated biomass differences were 40.7% in B73 and 38.2% in EV8728SR. Mycorrhization intensity declined with NaCl (P = 0.011). Conclusion: EV8728SR was the stronger-performing genotype, and Ri inoculation produced a modest average biomass benefit. Because interactions were not significant, the larger percentage differences at severe salinity are descriptive. Germination responses represent the inoculum treatment, not established symbiosis.

Background: Water deficit substantially limits maize growth and productivity, while lipoxygenase-derived signalling and arbuscular mycorrhizal symbiosis may influence plant responses to water stress. However, the extent to which maize 9-lipoxygenase mutants differ in biomass and physiological responses to graded water deficit, and whether Rhizophagus irregularis modifies these responses in a genotype-dependent manner, remains unclear. Objective: This study aimed to evaluate genotype-dependent biomass responses of B73, B73lox3-4, B73lox12-1, and W438 under different water regimes; compare absolute and proportional biomass tolerance; determine whether Rhizophagus irregularis inoculation modifies water-deficit responses in a genotype-dependent manner; and assess whether tissue water content and antioxidant responses support the observed biomass patterns. Study Design: The study tested maize line B73; its near-isogenic 9-lipoxygenase mutants B73lox3-4 and B73lox12-1; and the comparator line W438 across 100%, 50%, and 10% soil water-holding capacity (WHC), with non-inoculated and Rhizophagus irregularis DAOM 197198 treatments. Place and Duration of Study: The experiment was conducted under controlled conditions at Institut National Polytechnique Félix Houphouët-Boigny (INP-HB), Yamoussoukro, Côte d'Ivoire, between February and March 2025. Methodology: Total plant dry biomass was the primary endpoint. The reanalysis used a three-factor model with HC3 heteroscedasticity-robust Type III tests, Tukey-adjusted genotype comparisons within every inoculation × water panel, and bootstrap confidence intervals for biomass-based tolerance indices. Results: Total biomass differed by genotype (F₃,₈₅ = 35.62, P < 0.0001), water regime (F₂,₈₅ = 128.34, P < 0.0001), and their interaction (F₆,₈₅ = 4.40, P = 0.000647). Under 10% WHC, model-estimated biomass was greatest for B73lox3-4 (13.76 g without inoculation and 16.75 g with R. irregularis); with inoculation, B73lox3-4 exceeded all three comparison genotypes by Tukey-adjusted grouping. Its severe-stress tolerance index was also highest (0.639 without inoculation and 0.800 with R. irregularis). B73lox12-1 showed comparatively strong proportional biomass retention without consistently matching the absolute biomass of B73lox3-4. Inoculation had no overall biomass effect (P = 0.689), and neither the inoculation × water interaction (P = 0.523) nor the genotype × inoculation × water interaction (P = 0.284) was significant. Antioxidant capacity was strongly genotype dependent but did not show a genotype × water interaction. Conclusion: These results identify B73lox3-4 as the strongest biomass-based performer in this seedling assay, while showing that the R. irregularis treatment did not confer a uniform or genotype-specific buffering effect. Overall, differences among maize genotypes were more important than fungal inoculation in determining seedling biomass under water deficit.

Aims and Study Design: Arbuscular mycorrhizal fungi (AMF) can alter plant responses to salinity, but their effects depend on host genotype and may intersect with oxylipin signaling. We tested whether the maize 9-lipoxygenase gene ZmLOX3 and Rhizophagus irregularis DAOM 197198 were associated with contrasting responses in B73, its near-isogenic knockout line B73lox3-4, and the West African cultivar EV8728SR. Place and Duration of Study: The assay was conducted in the Laboratory of Phytopathology and Plant Biology at the Institut National Polytechnique Félix Houphouët-Boigny, Yamoussoukro, Côte d’Ivoire, from February to March 2024. Methodology: Non-inoculated and inoculated plants were exposed to 0, 68, or 102 mM NaCl. Data were analyzed using full salinity × inoculation × genotype models, followed by multiplicity-adjusted contrasts. Results: Salinity reduced growth, dry biomass, and tissue water status and increased Na⁺/K⁺ ratios. AMF responses varied by organ, genotype, and salinity: inoculation increased leaf biomass in several treatment combinations but reduced root biomass or relative water content in others. Three-way interactions were detected for leaf (P = 5.12 × 10⁻⁵), root (P = 7.74 × 10⁻⁷), and stem (P = 3.33 × 10⁻⁷) Na⁺/K⁺ ratios. Under severe salinity with AMF, the model-estimated root Na⁺/K⁺ ratio was 0.180 in B73, 0.0239 in B73lox3-4, and 0.0580 in EV8728SR. EV8728SR generally had the greatest absolute productivity, whereas relative stress indices sometimes favored B73 or B73lox3-4. Salinity also reduced mycorrhizal intensity, arbuscular abundance, and spore density. Conclusion: ZmLOX3 status was associated with AMF responses in root ion balance and water relations, but the knockout did not show universal salt tolerance. Selection should therefore combine absolute productivity, relative stability, ion homeostasis, and organ-specific AMF responses.

Large-scale production of Bacillus thuringiensis, one of the most widely used biopesticides, is often limited by the high cost of conventional culture media. In this study, fermented cassava paste water (EFM), ripe mango pulp juice (CM), and cashew apple juice (JPC) were evaluated as alternative substrates for the liquid fermentation of B. thuringiensis var. kurstaki HD-1. Physicochemical analyses revealed acidic pH values and classified the substrates into two clusters: CM with high C/N ratios, organic matter, total sugars, and proteins, and EFM and JPC with lower C/N ratios and nutrient levels. Fermentation results indicated that JPC supported the highest biomass production (8.29 × 10¹³ CFU mL⁻¹), exceeding that in the standard Tryptone Soy Broth (TSB) medium. However, CM promoted the highest sporulation rate (1.46 × 10¹³ CFU mL⁻¹) and the greatest bioactive lipopeptides—iturins (102.2 mg L⁻¹) and surfactins (554.7 mg L⁻¹)—surpassing TSB. The antifungal activity of crude fermented CM, EFM, and TSB was evaluated against Sclerotium rolfsii. All samples significantly inhibited mycelial growth of the pathogen with no significant differences among substrates or concentrations tested. This study highlights the potential of B. thuringiensis-fermented agrowaste as a cost-effective, environmentally friendly biocontrol tool for Sclerotium rolfsii.

Understanding the composition and dynamics of insect pest communities is crucial for developing effective and sustainable management strategies in oil palm ( Elaeis guineensis Jacq.) production systems. This study provides an updated inventory and ecological analysis of insect pests associated with industrial oil palm plantations in southwestern Côte d’Ivoire. The objective was to characterize pest diversity, abundance, and damage intensity across plantations of different phenological stages. Sampling was conducted during the late rainy to early dry season (March to July 2024) across three strata: Young Non-Productive Crops (YNPC), Young Productive Crops (YPC), and Mature Crops (MC). A total of 30,380, 717, and 882 palms were respectively examined in these strata. Insects were collected from a single frond per tree and identified using both morphological keys and image-recognition tools, with confirmation at the Entomology and Agricultural Zoology Laboratory of INP-HB (Yamoussoukro). Ecological indices, including species richness (S), Shannon diversity (H′), evenness (E), and similarity (Jaccard and Sørensen), were calculated to compare community structures. Ten pest species belonging to nine families and three orders (Coleoptera, Lepidoptera, and Orthoptera) were recorded. Species composition varied markedly with plantation age. Oryctes monoceros dominated in YNPC (Ar = 100%), Zonocerus variegatus in YPC (Ar = 72.14%), and Coelaenomenodera lameensis in MC (Ar = 91.70%). Species richness and diversity increased with age (S = 1 to 8; H′ = 0 to 0.72), whereas evenness remained low (E ≤ 0.24), indicating strong dominance by a few species. Similarity indices revealed complete faunal turnover between young and mature strata, confirming a clear ecological succession. Multivariate analyses revealed near-complete faunal turnover between strata (ANOSIM R = 1.0, p = 0.001), with hierarchical clustering perfectly grouping plots according to plantation age. Damage intensity followed the same trend: minimal in YNPC (mainly due to O. monoceros), moderate in YPC, and severe in MC, where C. lameensis caused up to 78.68% moderate and 2.49% severe damage. These results demonstrate that pest pressure and community complexity increase with the maturity of oil palm. Effective pest management, therefore, requires a phenology-based integrated approach, combining preventive measures in young plantations with regular entomological monitoring and biological or selective chemical control in mature ones. Continuous surveillance and the conservation of natural enemies are crucial for enhancing the ecological resilience and sustainability of Ivorian oil palm agroecosystems.

Aims: The present study aimed to evaluate the cross-pathogenicity of Colletotrichum isolates obtained from different hosts and production zones using substitute hosts. Study Design: The experimental design followed a completely randomized layout with 19 treatments and five replicates. Place and Duration of Study: The in vitro assay was conducted in the Plant Pathology and Plant Biology Laboratory at the Institut National Polytechnique Félix HOUPHOUET-BOIGNY, Côte d’Ivoire. Methodology: A total of 19 morphological groups of Colletotrichum sp. isolates were selected from a collection of 67 isolates obtained initially from avocado and banana fruits and characterized microscopically. Cross-inoculation assays were conducted on the substitute hosts 'Lula' (Avocado) and 'Grande Naine' (banana). Lesion diameters were measured along two perpendicular axes passing through the center of each lesion. Results: The isolates induced lesions of varying diameters ranging from 2.9 ± 6.5 mm to 24.6 ± 5.2 mm. All 11 Colletotrichum sp. groups isolated from Avocado caused lesions on banana fruits. Conversely, among the eight groups isolated from banana, only three isolates (KB17A, KB37A, and KB06A) produced lesions on avocado fruits. Analysis of variance revealed highly significant differences (P = .001) in lesion diameter among the Colletotrichum isolates at the 5% significance level, allowing for their classification into five homogeneous groups on Avocado and eight on banana. Some lesions were smaller or comparable in size to those observed on the control fruits. Conclusion: These findings demonstrate that several Colletotrichum isolates are capable of cross-infecting different fruit hosts. The identification of both host-specific and polyphagous isolates suggests potential implications for disease epidemiology, highlighting the risk of pathogen spread between adjacent crops. This knowledge is crucial for developing integrated management strategies, such as advising against the intercropping of susceptible hosts and informing targeted fungicide application programs in Côte d’Ivoire.

The search for effective and environmentally sustainable bioherbicides is a key objective in integrated weed management. This study evaluated the herbicidal potential of bergamot ( Citrus bergamia ) juice, a by-product of the essential oil industry, based on its high acetic acid content. Field experiments were conducted using a randomized complete block design to test five application rates (1,500, 1,200, 900, 600, and 300 L ha ^-1 ) on two contrasting weed communities: young regrowth (one week after mowing) and established weeds (four months after mowing). Efficacy was assessed over 60 days using the Henderson-Tilton formula and the European Weed Research Council (EWRC) rating scale. Soil pH was analyzed post-trial to detect acidification. A central finding was the stark contrast in efficacy based on weed growth stage. On established weeds, the rates of 1,500 L ha ^-1 and 900 L ha ^-1 provided the best control, with a residual activity of 30-45 days and efficacy >90% for up to 45 Days After Application (DAA). In sharp contrast, the treatment was largely ineffective on young regrowth, with even the highest doses providing only transient control that declined to very poor efficacy (≤31%) by 60 DAA. Results demonstrated that bergamot juice provided effective control of a broad spectrum of broadleaf weeds, including Phyllanthus amarus and Ageratum conyzoides , but showed poor efficacy against several grass species, particularly Paspalum dilatatum . Critically, no significant or consistent changes in soil pH were detected following application. The findings confirm that bergamot juice is a viable contact bioherbicide for managing established broadleaf weeds without impacting soil acidity but is not suitable for controlling young regrowth. Further research is needed to optimize application strategies, determine its economic feasibility, and fully elucidate its efficacy spectrum for commercial adoption.