Charles Oluwaseun Adetunji

Synergetic effect of rhamnolipid from Pseudomonas aeruginosa C1501 and phytotoxic metabolite from Lasiodiplodia pseudotheobromae C1136 on Amaranthus hybridus L. and Echinochloa crus-galli weeds

Rhamnolipid (Rh) is a biosurfactant produced by the bacterial Pseudomonas aeruginosa. This present study investigates rhizospheric strain C1501 of P. aeruginosa with an accession number KF976394 with the best production of rhamnolipid: a biosurfactant. The partially purified rhamnolipid from strain C1501 and Tween 80 was tested on mycelial growth of wild strain C1136. The enzyme activities involved in biodegradation, as well as necrosis induction on the tested weeds, were performed using scanning electron microscopy. It was observed that the different concentrations of rhamnolipid tested enhanced the dry mycelia weight yield of Lasiodiplodia pseudotheobromae which has been established to be producing a phytotoxic metabolite for killing weeds. It was observed that strain C1136 had a high level of cellulase and xylanase enzyme activities during this study. The scanning electron microscopy showed that the mutant strain of C1136 combined with 0.003% v/v of rhamnolipid enhances biodegradability and a high level of necrosis on the tested weeds compared with that on the untreated weeds. The highest CMCase activities and xylanase activities were obtained on the fourth day from the phytotoxic metabolite produced from the mutant strain of L. pseudotheobromae when combined with 0.003% v/v of rhamnolipid. This study has shown that rhamnolipid can serve as an adjuvant in order to enhance the penetrability of bioherbicide active ingredient for controlling weeds.

Isolation, identification, characterization, and screening of rhizospheric bacteria for herbicidal activity

AbstractThe consistent application of agrochemical herbicides has been reported to impact negatively on human health, environment, and food safety, and facilitated the emergence of weed resistances. Rhizosphere bacteria (RB) of different crops were screened for antagonism against Amaranthus hybridus L. (pigweed) and Echinochloa crus-galli (L.) Beauv. (barnyard grass) using necrosis assay technique. A total of eight rhizosphere bacterial isolates (B1–B8) produced different degrees of leaf necrosis on target weeds with isolate B2 manifesting the most significant necrotic activity. The rhizospheric bacterium (B2) with the highest necrotic activity was identified using 16S rRNA sequencing technique and further investigated. Molecular, morphological, and biochemical characterizations confirmed B2 isolate to be Pseudomonas aeruginosa. On isolation with ethyl acetate, separation, defatting, purification, and flash chromatography, seven different fractions (fraction 1–fraction 7) were obtained out of which fraction 4 showed the highest necrotic activity in necrosis assay experiment. Preparative HPLC of fraction 4 resulted in a pure compound that completely inhibited seed germination and seedling development of pigweed and barnyard grass but remained non-antagonistic to other tested soil fungi used in this study. The result obtained from this present study consequently confirmed the antagonistic behavior of rhizosphere-inhabiting P. aeruginosa to the target weeds and qualified the suitability of bacterium as good alternative source of bioherbicide. Potential herbicidal formulation from P. aeruginosa will help reduce crop loss due to weed challenges while offering a partial solution to the use of agrochemicals and food security. ᅟ

Environmental fate and effects of granular pesta formulation from strains of Pseudomonas aeruginosa C1501 and Lasiodiplodia pseudotheobromae C1136 on soil activity and weeds

This work investigated the effect of variably formulated pesta granules containing wild and UV mutated Pseudomonas aeruginosa and Lasiodiplodia pseudotheobromae on the rate of CO2 evolution, organic carbon content, enzymatic activity (acidic and alkaline phosphatase, dehydrogenases, urease and protease) and representative soil microorganisms in the soils using different assay techniques. After the 35th day period of experiment, the pesta granule formulation BH4 showed the best evolution of CO2 (824 ± 6.2 mg CO2 kg-1 soil hr-1) as against control treatment (689 ± 3.7 mg CO2 kg-1 soil hr-1). Enzymes activities, organic carbon content of 3.8% on the 15th day of study and stable representation of microorganisms that include actinomycetes, fungi, heterogenous as well as soil nitrogen-mediatory bacteria were equally at their maximum level BH4 treatments. The phytotoxic assay showed no inhibitory effect on Solanum lycopersicum seeds and seedlings compared to the observed growth inhibition on the tested weeds (Amaranthus hybridus and Echinocholoa crus-galli) which corresponds with positive control glyphosate treatment. The glyphosate treated soil had the least critical results on parameters investigated during the study. The order of bioherbicidal activity is BH4>BH2>BH6>BH3>BH1>BH5>positive control. Results from this study confirmed the target efficacy of variably formulated pesta granules which is sustainable, cheap, ecologically suitable and recent. This is in addition to recognizing the microbial-derived formulations as characteristically potent alternative to chemical herbicides utility in agrosystems practice. Further study of the underlining factor responsible for the bioherbicidal performances of the variably formulated pesta granules and field trials are critical for their future commercialization.