Exploring new plant-associated rhizobacteria and reintroducing them to the crop-soil environment is among the strategies to reverse the declining quality of the agricultural soil environment. A total of 340 isolates were recovered from the rhizospheres of okra (Abelmoschus esculentus), leaf mustard (Brassica juncea), and brinjal (Solanum melongena). From among the total, 155 isolates (45.59%) were diazotrophs, and 122 (35.88%) and 127 (37.35%) were isolates with the solubilising activity of phosphate and potassium, respectively. Thirteen of the most promising isolates were identified by gas chromatography for their cellular fatty acid methyl esters: Escherichia vulneris (TC19), Klebsiella pneumoniae (BA5, SA19, SB22), Pantoea ananatis (TC22), Pseudomonas aeruginosa (BA46), Pseudomonas putida (BA29, BA37, SC5, SC14), Salmonella bongori (BC17), Salmonella enterica (BB2), and Shigella dysenteriae (BA16). Three Pseudomonas strains viz. P. aeruginosa BA46 and P. putida BA37 and SC5 were selected after enhancing root elongation and vigour of lettuce seedlings. The American lettuce growth performance in the non-circulating hydroponic system was established. The inoculation with rhizobacteria strains, SC5 and BA46, stimulated shoot and root biomass over uninoculated control plants. The inoculation of lettuce plants with isolates BA37, BA46 and SC5, produced significantly longer roots compared to uninoculated control plants. This study indicates the potential use of the strains BA46 and SC5 as candidates for the formulation and production of hydroponic nutrient solution fortified with beneficial bacteria.
SOil-surface Roots (SORs) are roots that elongate over or near the soil surface. They allow plants to escape waterlogging-caused hypoxia and high salinity that are often present in deeper soil. Quantitative evaluation is essential for understanding SOR function and identifying the genes and quantitative trait loci (QTLs) that control it. However, existing methods to evaluate SOR formation are laborious/slow or semiquantitative. Here, we describe a high-throughput quantitative SOR evaluation system that uses an overhead scanner. We evaluated SORs in 56 wild rice (Oryza glumaepatula) introgression lines (ILs) with the genetic background of O. sativa. The method can quantify the SOR area of a plant in less than 90 sec. During the image analysis process, multi-threshold segmentation on the scanned images reduced the reflection noise of the digital image and improved the accuracy of the estimation of SORs formation. The root surface areas of SORs of the O. glumaepatula ILs varied widely, which should make them well-suited for identifying SOR-related QTLs. The overhead scanner method has the potential to quantitatively and rapidly evaluate SORs developed on the soil surface.
Sugarcane (Saccharum spp.) growth and yield decrease in acidic soil (low pH and high Al content) conditions owing to impaired nutrient and water absorption. An efficient method to evaluate acid tolerance needs to be developed to utilize Erianthus arundinaceus to improve acid tolerance in sugarcane. Herein, we performed a root electrolyte leakage assay to quantitatively evaluate and compare the acid tolerance of the roots of sugarcane cultivar NiF8 and E. arundinaceus accession JW630 under various treatments of acid solutions in laboratory. Additionally, cellular damage of root was observed anatomically and their growth in acidic soil was verified by pot cultivation. To detect the interspecific difference in injury index of root by measuring electrolyte leakage, the following method was found suitable: initial washing for 15 min, acid stress treatment with 3% Al2(SO4)3 solution for 2 h, and leaking electrolyte from the damaged cells in ultrapure water for 2–4 h. The index was aligned with the relative growth rate (RGR) under acidic soil (pH 5.0), as E. arundinaceus with a lower index value exhibited a higher RGR. Callose, indicative of cellular damage, was deposited both after exposure to short-term and long-term acid stress in the exodermis of sugarcane, which showed higher injury index and lower RGR than those of E. arundinaceus, whereas callose deposition was not observed in E. arundinaceus even after acid stress treatments. Our results strongly suggest that the injury index measurements can be used to quantitatively evaluate differences in acid tolerance between sugarcane and Erianthus roots.
Strontium (Sr) is a known non-essential element for plants. However, its toxic effects at high concentration on plants remain unclear. Here the effects of Sr on the growth and phytotoxicity were investigated in Arabidopsis thaliana. The plants grown on a medium containing 10-mM Sr showed reduced root fresh weight (FW) and root elongation, which suggested that high Sr concentration could inhibit root growth. Assessment of Sr in the shoots and roots indicated that its concentrations increased in a dose-dependent manner. Sr treatment caused reduced calcium (Ca) levels in a dose-dependent manner, while photosynthetic pigments were also reduced. Evans blue staining of shoots and roots treated with 10-mM Sr revealed that cell death was induced by Sr accumulation. Addition of potassium iodide (KI), a reduction compound, in Sr containing agar medium to determine the relationship between reactive oxygen species (ROS) and Sr toxicity showed that it could alleviate the Sr toxicity to growth. The 3,3'-Diaminobenzidine (DAB) detection of ROS production in the leaves and roots treated with 1- and 10-mM Sr confirmed that cell death was induced by ROS.
In this study, two experiments were conducted to evaluate the genotypic variation of rice root system distribution and root activity in response to short-term drought conditions. Seven rice genotypes were used, of which one (Rexmont) showed the greatest reduction in shoot biomass under drought, and two (Swarna and KDML105) showed the least reduction in shoot biomass under drought in both experiments. In a phytotron experiment (Experiment 1) in which root hydraulic conductivity (Lpr) of 21-day-old rice plants was evaluated in well-watered (control) and dry down (drought) conditions, the Lpr of Swarna, KDML105, and IRAT109 were significantly lower under drought compared to the control. In a field experiment (Experiment 2) conducted in the 2013 wet season at IRRI, stomatal conductance, bleeding rate, and root surface area density (RSAD) at 0-15, 15-30, 30-45, and 45-60 cm soil depths were measured in an irrigated (control) and rainfed (drought) treatments. Swarna, KDML105, and FR13A showed significant reductions in RSAD at 0-30 cm depth under drought in the field compared to the control, while Rexmont and IRAT109 showed no significant changes. In addition, Rexmont and Swarna both maintained higher bleeding rates than the other genotypes. Based on the root hydraulic and architectural traits of contrasting genotypes, we conclude that the bleeding rate did not explain the genotypic variations in the maintenance of shoot biomass, and that reducing shallow root growth and Lpr in response to drought conferred the best ability to maintain shoot biomass under short-term drought conditions.
The root hydraulic conductance of rice is often measured using the pressure chamber method only for the main stem at the seedling stage, as it is difficult to evaluate at a more advanced growth stage with tillers due to the high risk of pressure leakage from the gaps between the tillers. The aim of this study was to identify techniques that are effective for prevention of air leakage and an improvement in the success rate of root hydraulic conductance measurements in rice plants with tillers. Using three rice (Oryza sativa L.) genotypes, FR13A (aus), KDML105 (indica), and Swarna (indica), the root hydraulic conductance of the main stem and four tillers were calculated using the pressure chamber method at 98, 104, and 95 days after sowing, respectively, using the following three techniques: 1) careful detachment of dry leaf sheaths, 2) ensuring spacing between tillers and an appropriate amount of silicone in the socket, and 3) pre-fixing the socket to prevent vertical misalignment. Using these three techniques, we achieved a success rate of 92.8% (13 of 14 plants) for root hydraulic conductance measurements in the genotypes. Additionally, we show that genotypic variation in root hydraulic conductance exists at the late vegetative stage, and that the growth stage can have a significant effect on root hydraulic conductance values. In conclusion, this study presents a detailed pressure chamber method for measuring root hydraulic conductance in rice plants with tillers, reducing the risk of pressure leakage, and improving the success rate of the measurement.
The effects of hydrogen sulfide (H2S), released from the donor sodium hydrosulfide (NaHS), on maize seedlings grown hydroponically for 6 days were investigated. Plant biomass, malondialdehyde (MDA), hydrogen peroxide (H2O2), superoxide (O2•−) content, and root exudates (organic acids) were measured. Results showed that 100 and 200 µM NaHS is the most appropriate and suitable concentration for the growth and development of maize seedlings, without affecting the MDA and H2O2 contents but altering the O2•−. In addition, high concentrations of 500 and 1000 µM NaHS adversely affected these parameters compared with the control (CK). The pH of the root exudates declined under NaHS treatments. The organic acids in the root exudates, including fumaric, acetic, formic, and malic acids exhibited higher contents at 100 µM NaHS treatment, the lactic and citric acids were higher at both 100 and 200 µM NaHS. In contrast, oxalic acid was reduced at all NaHS concentrations compared with the CK. Low contents of all the organic acids analyzed were found under 500 and 1000 µM NaHS treatment. In conclusion, all the above parameters were affected by the application of NaHS, while higher NaHS concentration was toxic for maize seedlings.