Identification, evaluation and selection of a bacterial endophyte able to colonize tomato plants, enhance their growth and control Xanthomonas vesicatoria, the causal agent of the spot disease

Beneficial endophytes are key factors in plant productivity and disease control; therefore, research is ongoing to characterize the potential of endophytes as microbial inoculants to promote plant growth and act as biocontrol agents. In this study, we searched for and identified a set of endophytes occurring naturally in a few important crops. Beneficial endophytes were shown to antagonize several important fungi and bacteria, in particular those affecting tomato (Solanum lycopersicum), including Rhizoctonia solani, Alternaria alternata, Clavibacter michiganensis pv. michiganensis, Ralstonia solanacearum, and Xanthomonas vesicatoria. We characterized the most promising as potential inoculants of tomato, aiming to foster plant growth and control the bacterial spot disease caused by Xanthomonas vesicatoria. Among the selected endophytes, we identified a novel streptomycetes, taxonomically related to Streptomyces avermitilis and a pseudomonad, identified as Pseudomonas granadensis. The beneficial effects of these two bacteria, used as single inoculants or as a combination of both, were seen in a significant increase in root and shoot length (approximately 31% and 34% for the streptomycetes and 18% and 16% for the pseudomonad) and dry root biomass (90% for the streptomycetes and 70% for the pseudomonad). Additionally, both inoculants reduced disease progression and severity following inoculation with X. vesicatoria. There was no significant difference between plants treated with single inoculants and plants treated with both. The penetration and efficient colonization of tomato tissues by a green fluorescent protein-tagged culture of the streptomycetes was observed by confocal microscopy, confirming its endophytic nature

Plant growth promotion and fungal antagonism of endophytic bacteria for the sustainable production of black pepper (Piper nigrum L.)

[[abstract]]In this study, one hundred and six endophytic bacteria were isolated from the roots of black pepper (Piper nigrum L.) cultivated in the central highlands of Vietnam, which is the largest region of black pepper production in the country. Among these, there were sixteen potent isolates selected for further screening. After the screening, four promising isolates were selected: EB.CP32, which possessed the highest nitrogen fixation of 12.02 µg/ml, EB.CS30, which had the highest phosphate solubilization of 8.61 µg/ml, EB.DC16, which was able to produce the highest IAA (33.64 µg/ml), and EB.EK2, which possessed high three activities. The isolates and their complexes were applied to black pepper seedlings to evaluate their effectiveness in a greenhouse. The results showed that the bacteria were able to improve the soil fertility in areas such as a 5–15% increase in N; a 100–150% increase in available phosphorous; and an increase in leaf nutrient uptake (5–7% N, 30–60% P, and 70–90% Zn), thereby enhancing the disease resistance of black pepper. These isolates promoted the growth of black pepper up to approximately a 100% increase compared to the control. From a bioassay in the greenhouse, RB.CS30 and RB.EK2 were selected for analysis. Further investigation found seven potent antifungal compounds from the culture broth of RB.EK2 by LC–MS: 1-cyclohexyl-2-(3-methyl-2-propan-2-ylbutyl) guanidine (C1); dibenzoylacetylene (C2); 6-N,7-dimethylquinoline-5,6-diamine (C3); 2-(1,3-dihydroisoindol-2-yl)-N,N–diethylethanamine (C4); piperazine 1-butyl-4-(1-phenylpropan-2-yl) (C5); 10-(2,6-diphenylpyran-4-ylidene) anthracen-9-one (C6); and 3-methyl-2-naphthalen-1-yl-2-(2-piperidin-1-ylethyl) pentanenitrile (C7). Therefore, RB.CS30 and RB.EK2 were found to be promising endophytic bacteria for the plant growth promotion and biocontrol of black pepper.[[sponsorship]]MOST[[notice]]補正完

Growth and development dynamics in agronomic crops under environmental stress

Plants are exposed to different kinds of adverse environmental conditions during their life cycle that ablate their productivity. These environmental fluctuations have detrimental effects on the crops in terms of growth and development. Plants are highly susceptible to abiotic stresses including drought, salinity, high temperature, and increasing heavy metal concentration. The changing events related to climatic conditions are the signs of consternation for crops to maintain their productivity. Due to global warming, drought and high temperature are serious concerns regarding effective crop production. Salinity also adversely affects growth and productivity by disrupting normal physiology and biochemistry of plants. It causes osmotic disturbance, nutritional imbalance, malfunction of photosynthetic machinery, and oxidative stress. Rapid urbanization and industrialization are polluting the arable lands with heavy metals which not only affects crop productivity but also interferes with human health. In the modern era, heavy metals, like lead, cadmium, chromium, mercury, and copper are main environmental hazards, especially in regions of higher anthropogenic activity. Contamination of agricultural soils with heavy metals is a serious concern owing to its deleterious effects on agricultural productivity, phytotoxicity, food safety, and quality of the environment with ultimate impact on human health. All these abiotic stresses negatively affect several growth and developmental processes of plants which reduce the productivity of agronomic crop and also deteriorate the quality of produce. To cope with the situation, it is inevitable to understand the adverse effects of these abiotic factors on crop plants. This chapter provides comprehensive information on the impacts of abiotic stresses on crop plants

Exploitation of Rhizosphere Microbiome Services

The rhizosphere is a soil hot spot where, due to a tight plant-bacteria interaction, plants recruit a beneficial microbiome, enhancing its density and activity. Rhizosphere microbial communities have the potential to provide several services, and their management and \u201cengineering\u201d can be exploited to set up agro-environmental biotechnologies. In this chapter, after a brief overview of the array of services that we can obtain from rhizosphere beneficial microbiome, two case studies are presented: i) the exploitation of plant growth promoting bacteria to increase plant tolerance to drought, potentially able to improve crop plants yields in arid and semi-arid lands, ii) the exploitation of plant biostimulation effect over degrading microbial populations in the rhizosphere, sustaining phyto-rhyzo-remediation approaches in PCB contaminated soils. In each case study the experimental settings, the in vitro and in vivo tests, the result evaluation and modelling are reported, together with a discussion of the critical issues