Bacterial Inoculants Mitigating Water Scarcity in Tomato: The Importance of Long-Term in vivo Experiments

Deciphering the interaction of bacteria inoculants with the recipient endophytic community in grapevine micropropagated plants

Engineering the plant microbiome with beneficial endophytic bacteria can improve the growth, health, and productivity of the holobiont. Here, we administered two beneficial bacterial strains, Kosakonia VR04 sp. and Rhizobium GR12 sp., to micropropagated grapevine cuttings obtained via somatic embryogenesis. While both strains colonized the plant endosphere, only Rhizobium GR12 sp. increased root biomass under nutritional-deficit conditions, as supported by the plant growth promotion traits detected in its genome. Phylogenetic and co-occurrence analyses revealed that the plant native bacterial community, originally dominated by Streptococcaceae and Micrococcaceae, dramatically changed depending on the inoculation treatments, as invading strains differently affected the relative abundance and the interactions of pre-existing taxa. After 30 days of plantlets' growth, Pantoea became a predominant taxon, and considering untreated plantlets as references, Rhizobium sp. GR12 showed a minor impact on the endophytic bacterial community. On the other hand, Kosakonia sp. VR04 caused a major change in community composition, suggesting an opportunistic colonization pattern. Overall, the results corroborate the importance of preserving the native endophytic community structure and functions during plant microbiome engineering.IMPORTANCEA better comprehension of bacterial colonization processes and outcomes could benefit the use of plant probiotics in the field. In this study, we applied two different beneficial bacteria to grapevine micropropagated plantlets and described how the inoculation of these strains impacts endophytic microbiota assembly. We showed that under nutritional deficit conditions, the response of the receiving endophytic bacterial communities to the invasion of the beneficial strains related to the manifestation of plant growth promotion effects by the inoculated invading strains. Rhizobium sp. GR12 was able to preserve the native microbiome structure despite its effective colonization, highlighting the importance of the plant-endophyte associations for the holobiont performance. Moreover, our approach showed that the use of micropropagated plantlets could be a valuable strategy to study the interplay among the plant, its native microbiota, and the invader on a wider portfolio of species besides model plants, facilitating the application of new knowledge in agriculture.

Potential of algal-based products for the management of potato brown rot disease

BACKGROUND

Ralstonia solanacearum causes potato brown rot disease, resulting in lower crop's production and quality. A sustainable and eco-friendly method for controlling the disease is required. Algae's bioactive chemicals have shown the potential to enhance plant defenses. For the first time, the efficacy of foliar application of Acanthophora spicifera and Spirulina platensis seaweed extracts, along with the utilization of dried algal biomasses (DABs) of Turbinaria ornata and a mixture of Caulerpa racemosa and Cystoseira myrica (1:1)on potato yield and brown rot suppression were investigated under field conditions. Field experiments were conducted in three locations: Location 1 (Kafr Shukr district, Kaliobeya governorate), Location 2 (Moneira district, Kaliobeya governorate), and Location 3 (Talia district, Minufyia governorate). Locations 1 and 2 were naturally infested with the pathogen, while location 3 was not. The study evaluated potato yield, plant nutritive status and antioxidants, soil available nitrogen-phosphorus-potassium (N-P-K), and organic matter percentage. Additionally, the shift in soil microbial diversity related to R. solanacearum suppression was examined for the most effective treatment.

RESULTS

The results revealed that seaweed extracts significantly increased potato yield at all locations, which correlated with higher phosphorus absorption, while T. ornate DAB increased potato yield only at location 2, accompanied by noticeable increases in soil nitrogen and plant phosphorus. The mixed DABs of C. racemosa and C. myrica demonstrated greater disease suppression than foliar applications. The disease-suppressive effect of the mixed DABs was accompanied by significant increases in flavonoids and total antioxidant capacity (TAC). Moreover, the application of mixed DABs increased soil bacterial biodiversity, with a higher abundance of oligotrophic marine bacterial species such as Sphingopyxis alaskensis and growth-promoting species like Glutamicibacter arilaitensis, Promicromonospora sp., and Paenarthrobacter nitroguajacolicus in all three locations compared to the untreated control. Klebsiella sp., Pseudomonas putida, and P. brassicacearum abundances were increased by the mixed DABs in Location 1. These species were less abundant in locations 2 and 3, where Streptomyces sp., Bacillus sp., and Sphingobium vermicomposti were prevalent.

CONCLUSIONS

The results demonstrated that the used seaweed extracts improved potato yield and phosphorous absorption, while the mixed DABs potentially contributed in disease suppression and improved soil microbial diversity.

Effectiveness of Phosphate and Zinc Solubilizing Paenarthrobacter nitroguajacolicus P1 as Halotolerant Rhizobacterium with Growth-Promoting Activity on Pistacia vera L

Plant growth-promoting rhizobacteria (PGPR) are beneficial microorganisms to develop microbial fertilizers. Biofertilizers can accelerate plant growth and enhance crop yields. The current research aimed to isolate and identify rhizobacterium with plant growth-promoting activity in the rhizospheric region of pistachio trees in arid and salty region of Iran. In the present study, 26 bacterial isolates were isolated from the rhizospheric region of the pistachio trees. Plant growth-promoting characteristics of isolated bacteria, including the ability to solubilize phosphate and zinc, produce hydrolyzing enzymes, and hydrogen cyanide (HCN), as well as synthesize indole-3-acetic acid (IAA) were evaluated through in vitro assays. Based on these activities, five multifunctional bacterial strains designated P1, P10, P11, P17, and P19 were then applied and their effect was studied on the growth and physiological properties of Pistacia vera L. seedlings by pot experiments under normal conditions. Finally, the most efficient strain has been identified by analysis of the 16S rRNA gene sequence. According to the results, all the isolated bacteria exhibited considerable plant growth-promoting properties. They could produce amylase (n = 26, 2 ± 0.00-13 ± 0.42 mm), lipase (n = 24, 2 ± 0.00-9 ± 0.23 mm), protease (n = 20, 1 ± 0.00-17 ± 0.0 mm), indole-3-acetic acid (n = 26, ranging from 5.05 ± 0.08 to 11.5 ± 0.11 μg/mL) and HCN (n = 24). Six isolates showed significant growth at 20% w/v NaCl. Inoculation of P1, P17, and P19 increased chlorophyll, carotenoid, and phenolic content in treated Pistacia vera L. seedlings. P1 and P11 inoculated plants showed an enhanced level of anthocyanin and proline. These most effective strains were catalase and Gram-positive bacterium and showed antibiotic sensitivity. They can consider as halotolerant PGPR, due to the growth in the presence of NaCl (20% w/v). Finally, P1 inoculated plants exhibited higher levels of sugar content. This strain showed the most similarity (99.92%-1322 bp) to Paenarthrobacter nitroguajacolicus based on 16S rRNA gene sequence. Based on the results, Paenarthrobacter nitroguajacolicus P1 with multiple PGPR can be applied as a promising candidate in the soil-Pistacia vera L. system to improve their productivity and health by increasing available nutrient content, improving photosynthetic parameters, and producing phytohormones and HCN.