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EP-4735578-A1 - PARARHIZOBIUM STRAINS, COMPOSITIONS AND USES THEREOF AS PLANT GROWTH STIMULANTS

EP4735578A1EP 4735578 A1EP4735578 A1EP 4735578A1EP-4735578-A1

Abstract

The present invention provides a Pararhizobium strain selected from: (a) a strain deposited in the Spanish Type Culture Collection (CECT) with the accession number CECT30825; (b) a strain deposited in the Spanish Type Culture Collection (CECT) with the accession number CECT30826; or (c) a mutant thereof, wherein the mutant: (i) is obtained from CECT30825 or CECT30826 strain, and (ii) retains one or more of the following properties: (ii.1) induction of plant tolerance to chilling temperature; (ii.2) induction of plant tolerance to freezing temperature; (ii.3) induction of plant growth; (ii.4) increased plant yield; and (ii.5) induction of plant tolerance to water deprivation and/or drought. The invention further provides compositions, uses and methods based on the strains of the invention. Advantageously the strains of the invention are of broad-spectrum, providing an effective protective effect in several abiotic stresses, such as low temperatures, water deprivation and/or drought and saline environment.

Inventors

  • ALCÁZAR HERNÁNDEZ, Rubén
  • ATANASOV, Kostadin Evgeniev

Assignees

  • Universitat de Barcelona

Dates

Publication Date
20260506
Application Date
20240620

Claims (15)

  1. 1. A Pararhizobium strain selected from: (a) a strain deposited in the Spanish Type Culture Collection (CECT) with the accession number CECT30825, (b) a strain deposited in the Spanish Type Culture Collection (CECT) with the accession number CECT30826, or (c) a mutant thereof, wherein the mutant: (i) is obtained from CECT30825 or CECT30826 strain, and (ii) retains one or more of the following properties: (ii.1) induction of tolerance to chilling temperature; (ii.2) induction of tolerance to freezing temperature; (ii.3) induction of plant growth; and (ii .4) increased yield.
  2. 2. A bacterial culture comprising the strain or the mutant thereof according to claim 1.
  3. 3. The bacterial culture of claim 2, which is an inoculation product.
  4. 4. A supernatant obtained from the strain as defined in claim 1 , said supernatant being obtained by a process comprising: (i) inoculating the strain in a suitable culture medium; (ii) subjecting the inoculated culture medium to suitable growth conditions; (iii) separating the cells from the culture medium of step (ii); (iv) collecting the supernatant; and (v) optionally subjecting the supernatant to a concentration step.
  5. 5. A process for obtaining a viable cell suspension derived from the strain as defined in claim 1 , the process comprising: (i) inoculating the strain in a culture medium, (ii) subjecting the inoculated culture medium of the step (i) to conditions suitable for growth of the strain, and (iii) optionally subjecting the medium resulting from step (ii) to a concentration step.
  6. 6. A method to obtain a mutant of the strain as defined in claim 1 , comprising the step of subjecting the strain CECT30825 or CECT30826 to a DNA recombinant technique, preferably mutagenesis.
  7. 7. A composition comprising the strain according to claim 1 , the bacterial culture according to any one of the claims 2-3 or the supernatant according to claim 4, and one or more agriculturally acceptable compounds.
  8. 8. The composition according to claim 7 wherein the strain is present at a concentration from 10 5 CFU/ml to 10 12 CFU/ml, particularly from 10 7 to 1O 10 CFU/rnL, particularly 10 8 CFU/mL.
  9. 9. The composition according to any one of claims 7-8, which comprises at least one additional growth promoting agent; particularly the composition comprises the strain CECT30285; particularly the composition comprises the strain CECT30825 and CECT30286.
  10. 10. A kit comprising an effective amount of the strain as defined in claim 1 , the bacterial culture according to any of the claims 2-3, the supernatant according to claim 4, or the composition according to any one of claims 7 to 9.
  11. 11. Use of the Pararhizobium strain as defined in claim 1 , the bacterial culture as defined in any of the claims 2-3, the supernatant as defined in claim 4, or the composition as defined in any of the claims 7-12, as a growth plant promoter.
  12. 12. Use of the Pararhizobium strain as defined in claim 1 , the bacterial culture as defined in any of the claims 2-3, the supernatant as defined in claim 4, or the composition as defined in any of the claims 7-9, for increasing abiotic stress tolerance, biomass and/or yield of a plant.
  13. 13. A method for promoting the growth in a plant, the method comprising applying to the plant the strain as defined in claim 1 , the bacterial culture as defined in any of the claims 2-3, the supernatant as defined in claim 4, or the composition as defined in any of the claims 7-9.
  14. 14. A method for increasing abiotic stress tolerance, biomass and/or yield of a plant, the method comprising applying to the plant the strain as defined in claim 1 or 9, the bacterial culture as defined in any of the claims 2-3, the supernatant as defined in claim 4, or the composition as defined in any of the claims 7-9.
  15. 15. The use of claim 12 or the method of claim 14, wherein the abiotic stress is selected from the group consisting of: - chilling temperature; - freezing temperature; - saline stress; and - water deprivation and/or drought.

Description

Pararhizobium strains, compositions and uses thereof as plant growth stimulants FIELD OF THE INVENTION The present invention relates to the field of plant stimulants. In particular, the present invention provides new strains of Pararhizobium genera, as well as compositions and uses thereof in promoting plant growth. STATE OF THE ART Controlling plant growth and mitigating the adverse impact of environmental stressors are crucial factors that dictate the yield of cultivated crops. Abiotic stresses can be prevented by optimizing plant growth conditions through the use of plant biostimulants. Plant biostimulants include a diversity of substances and microorganisms that enhance plant growth by improving plant metabolism to induce yield increases and enhanced crop quality; increase plant stress tolerance and recovery from stresses; facilitate nutrient assimilation, translocation and use; and their effects operate through different mechanisms than fertilizers (Calvo et al., 2014). Over the past few decades, there has been a significant rise in the application of microbial inoculants in agriculture (Li et al., 2022). Microbial inoculants mainly include free-living bacteria, fungi, and arbuscular mycorrhizal fungi isolated from different sources (Berg, 2009). Plants face various environmental stresses, such as salt stress, extreme temperatures, drought, and flooding, among others, which can adversely affect their growth and productivity. The use of beneficial microbes offers a promising solution to alleviate these stresses and improve plant performance. Salt stress is a major threat to crop productivity, and beneficial microbes have been shown to enhance plant salt tolerance (Kumawat et al., 2023). For example, pea plants inoculated with Variovorax paradoxus 5C-2, which produces 1 -aminocyclopropane-1 -carboxylate (ACC) deaminase, showed increased photosynthetic rate, electron transport, balanced ion homeostasis, and biomass under salt stress at 70 mM and 130 mM NaCI (Q., Wang et al., 2016). Okra (Abelmoschus esculentus L.) plants treated with plant growth promoting rhizobacteria (PGPR) producing ACC also showed enhanced salt tolerance, increased antioxidant enzyme activities, and upregulated ROS pathway genes (Habib et al., 2016). Maize seedlings inoculated with Bacillus amyloliquefaciens SQR9 showed enhanced salt stress tolerance, including improved chlorophyll content, peroxidase/catalase activity, glutathione content for scavenging ROS, and reduced sodium levels in the plant (Chen et al., 2016). Wheat plants inoculated with the halotolerant Dietzia natronolimnaea showed upregulation of genes involved in the ABA-signaling cascade, salt overly sensitive (SOS) pathway, ion transporters, and antioxidant enzymes (Bharti etal., 2016). In tomato, treatment with strains of Bacillus sp. led to higher levels of total soluble sugar, proline, and chlorophyll as well as higher antioxidant enzyme activities in salt-stressed plants (Patani et al., 2023). Extreme temperatures, such as cold and heat stress, also pose significant challenges to crop productivity. The primary factors that cause low-temperature stress are freezing (temperatures below 0 °C) and chilling (temperatures between 0-15 °C). When plants experience freezing stress, the formation of ice crystals in the cells results in freezing dehydration and electrolyte leakage (Mitra et al., 2021). Some beneficial microbes have been shown to improve plant performance under extreme temperature conditions. For example, inoculation with Serratia nematodiphila, a gibberellin-producing PGPR, increased pepper growth under low temperature stress conditions (Kang et al., 2015). Burkholderia phytofirmans PsJN modulated sugar metabolism and reduced chilling damage to grapevine plantlets exposed to low temperature stress (Fernandez et al., 2012) and reduced the impact of freezing temperatures on photosynthesis in Arabidopsis thaliana (Su et al., 2015). Inoculation of tomato plants exposed to low temperatures with Pseudomonas vancouverensis OB155 and P. frederiksbergensis OS261 increased the expression of cold-acclimation genes and the antioxidant activity in leaf tissues (Subramanian and Smith, 2015). A consortium of three PGPR strains Bacillus cereus AR156, B. subtilis SM21 , and Serratia sp. XY21 provided enhanced chilling (4 °C) tolerance in tomato seedlings by stimulation of faster and higher accumulations of MDA, H2O2, soluble sugar and proline accumulation (C., Wang et al., 2016). In rice, a consortium of Bacillus amyloliquefaciens Bk7 and Brevibacillus laterosporus B4 enhanced plant growth and reduced stress symptoms in rice seedlings subjected to 0 ± 5 °C for 24 h, in correlation with reduced MDA and electrolyte leakage, increased proline, cholorophyll content and antioxidant enzyme activities (Kakar ef al., 2016). In spite of the efforts made there is still the need of providing plant growth promoters. SUMMARY OF THE INVENTION The present inventors have identified new str