IR6 exhibited the most notable agronomic performance, increasing seedling leaf area, fruit production, and fruit size under field conditions and demonstrating antagonistic activity against Fusarium oxysporum, confirming its potential as a biocontrol agent and PGPR.
Maize sheath blight caused by Rhizoctonia solani is a major constraint to maize production, particularly in tropical peatland ecosystems where environmental conditions favor pathogen development. This study evaluated the antagonistic potential of rhizosphere fungi isolated from the indigenous plant Solanum lasiocarpum Dunal (Terung Asam) against R. solani under in vitro conditions. Rhizosphere fungi were isolated and identified using morphological characteristics and ITS rDNA sequencing, while their antagonistic activity and volatile organic compound (VOC)-mediated inhibition were assessed using dual culture and sealed plate assays. Six fungal isolates were successfully recovered from the rhizosphere of S. lasiocarpum and identified as belonging to the genera Trichoderma (TA-1–TA-3) and Aspergillus (TA-4–TA-6). Among them, Trichoderma isolate TA-1 (82.8%) and Aspergillus isolate TA-4 (81.4%) exhibited the highest inhibition of R. solani, indicating strong antagonistic activity through competition, mycoparasitism, and antibiosis. In the VOC assay, Aspergillus isolates TA-4 and TA-5 showed the strongest inhibition of pathogen growth, suggesting the production of antifungal volatile metabolites. Molecular identification based on ITS sequencing and BLAST analysis confirmed that isolate TA-1 was Trichoderma asperellum (576 bp) and isolate TA-4 was Aspergillus welwitschiae (574 bp), both sharing 100% sequence similarity with reference sequences in GenBank. To our knowledge, this is the first report describing antagonistic fungi isolated from the rhizosphere of wild S. lasiocarpum as potential biological control agents against maize sheath blight caused by R. solani. These indigenous fungi represent promising candidates for the development of environmentally sustainable disease management strategies in tropical peatland agriculture.
Description of the subject. The sustainable rehabilitation of degraded soils is a major challenge. This study aims to evaluate the potential of indigenous plant-bacteria symbiotic associations for the phytoremediation of a degraded site. Objectives. To isolate and select Plant Growth-Promoting (PGP) bacterial strains adapted to local conditions to enhance the establishment of carob trees (Ceratonia siliqua), a species of significant socio-economic interest. Method. Sixty-four isolates consisting of actinobacteria or Pseudomonas fluorescens were obtained from the rhizosphere of pioneer legumes (Lotus creticus, Retama monosperma) from the site. A phenotypic screening assessed their PGP traits (indole-3-acetic acid [IAA] production, phosphate solubilization, fungal antagonism). The most promising isolates were used to inoculate carob seedlings grown for two months in a nursery on a sterilized substrate composed of the site's native alkaline and infertile soil. Growth parameters were measured and analyzed by Principal Component Analysis (PCA). Results. The screening identified isolates with complementary profiles: RP5 (high IAA production: 36.09 µg·mL-1), RP1 (phosphate solubilization: halo of 11 mm), and CAARL30 (antagonistic activity against Alternaria alternata, Aspergillus sp., Cladosporium sp., and Fusarium sp.). Isolate CAARL35 (Streptomyces sp.) showed a balanced profile of both IAA production and phosphate solubilization. Nursery trials confirmed the effectiveness of the inoculations. PCA identified the most effective treatments: isolate CAARL35, isolates RP1, RP2, RP5 (P. fluorescens), and the synergistic combination GAL4+RP1. Inoculation with CAARL35 induced the most significant improvements, increasing dry biomass by up to 41%, root length by 35%, and the number of leaflets by 77% compared to the non-inoculated control. Conclusions. This study demonstrates the potential of indigenous rhizobacterial strains, particularly Streptomyces sp. CAARL35, as an effective bioinoculant for enhancing carob tree growth under stressful soil conditions. The selection of high-performing plant-bacteria partnerships, adapted to local edaphic constraints, provides a promising and eco-friendly strategy for the rehabilitation of degraded ecosystems.
Preliminary evidence is provided of the potential of a Streptomyces levis strain as a PGP bacterium under saline conditions and Seed germination efficiency revealed that the 24 hrs culture of isolate H had a significantly greater effect on rice seed germination than the 48 hrs culture.
This study evaluated the biocontrol potential of ten commercially available microbial soil additives and fungicides against major soil-borne pathogens (Rhizoctonia solani, Fusarium oxysporum, Sclerotinia sclerotiorum and Diaporthe longicolla) to identify immediate, market-ready solutions for farmers, in the case of soil additives without the delay of product registration. In vitro dual cultures demonstrated strain- and pathogen-dependent antagonistic activity, with Pseudomonas and Bacillus being less effective than the tested Trichoderma strains. Regarding bacterial antagonists, the production of volatile organic compounds (VOCs) and lytic enzymes was confirmed in vitro, indicating potential mechanisms of antagonism. Compatibility tests on soybean plants demonstrated no negative effects on germination, overall growth, or nodule abundance in nearly all cases. In greenhouse bioassays, under high R. solani pressure (1.5%) microbial treatments did not significantly restore germination rate and seedling growth. However, T. harzianum T50 (Vitalin Trichoderma) and T. harzianum + P. fluorescens mixture (Trillus), significantly reduced hypocotyl lesion severity and increased the proportion of symptom-free seedlings. Overall, in planta efficacy was highly variable compared to the strong in vitro inhibition. Nevertheless, selected commercial strains show clear potential to mitigate severe disease symptoms under high R. solani pressure.
Nitrogen-fixing endophytic bacteria play an important role in improvingnitrogen availability and supplying growth-promoting factors to plants. This study evaluated the potential of endophytic bacterial isolates obtained from various plants growing under saline conditions based on their nitrogenase activity, indole-3-acetic acid (IAA) production, and ability to promote rice seedling growth. A bioassay was conductedusing rice seedlings grown in Fahraeusmedium adjusted to a salinity level of 4 dS m⁻¹. The experiment was arranged in a randomized complete block design with eight treatments consisting of an uninoculated control and seven selected endophytic bacterial isolates, with three replications. The measured responses included shoot length, root length, shoot dry weight, root dry weight, and total seedling biomass. Based on the bioassay results, two superior isolates, A1 and A2, were identified. The isolates exhibited nitrogenase activities of 1.223 and 1.780 µmol mL⁻¹ g⁻¹ h⁻¹, respectively, and produced IAA at concentrations of 7.819 and 7.794 mg L⁻¹, respectively. They increased root length by 13.66% and 15.44%, respectively, and resulted in numerically higher total seedling dry biomass, with values 51.99% and 34.68% higher than the uninoculated control, respectively. These findings indicate that the selected halotolerant nitrogen-fixing endophytic bacterial isolates can promote rice seedling growth under saline conditions and have potentialfor further development as biological fertilizers for rice cultivation on saline soils.
