Arbuscular mycorrhizal fungi and rhizobacteria attenuating drought stress in maize plants

Author(s)

Antonio Marcos Miranda Silva

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2023-05-16

Examining board members

Elke Jurandy Bran Nogueira Cardoso; German Andres Estrada Bonilla; Filipe Pereira Matteoli

• Advisor: Elke Jurandy Bran Nogueira Cardoso

Abstract

Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) are essential for enhancing plant health by increasing their tolerance to biotic and abiotic stresses. This study aimed to investigate the role of native AMF and PGPR screened from the Caatinga Biome, an extreme environment, in mitigating drought effects and promoting maize (Zea mays L.) growth. Three hypotheses were tested: (i) Caatinga-adapted plants harbour potential AMF and PGPR that can be screened and used as inoculants in maize crops; (ii) the effectiveness of a native AMF inoculum obtained from a harsh environment varies with drought levels, leading to changes in soil and plant microbiological parameters related to nutrient cycling and the plant antioxidant system; (iii) a combination of AMF and PGPR can enhance 33P uptake in maize plants under soil water stress. To test the first hypothesis, soil rhizosphere samples from Neoglaziovia variegate and Tripogonella spicata were sampled in Caatinga Biome, and the mycorrhizal community was characterized using high-throughput sequencing of the partial 18S rRNA gene. The results revealed that the community of arbuscular mycorrhizal fungi in the rhizosphere of each plant encompasses a unique composition, structure, and modularity, which can differentially assist them in the hostile environment. For the second hypothesis, a greenhouse experiment was carried out, using treatments simulating severe drought (30 % of water-holding capacity [WHC]), moderate drought (50 % of WHC), and no drought (80 % of WHC). The results showed that the better use of the AMF inoculum varied according to drought levels, with better performance observed under moderate drought due to an increase in plant biomass. Finally, to test the third hypothesis, a microcosm experiment was conducted to investigate the effect of a combination of AMF (Rhizophagus clarus) and PGPR (Bacillus sp.) on 33P uptake in maize plants under soil water stress. Overall, 33P facilitation was modulated by soil water content, with dual-inoculation and rhizobacteria alone being more efficient under severe drought, whereas under moderate drought conditions, mycorrhizae alone were more effective in promoting plant 33P uptake. In conclusion, this study highlights the potential of using AMF and PGPR as a combined strategy to promote plant growth and development under drought conditions. However, further research is needed to explore their potential for improving crop yields under non-controlled conditions. (AU)

• FAPESP's process: 19/13436-8 - Mitigation of water stress in maize (Zea mays L.) after arbuscular mycorrhizal fungi and growth promoting rhizobacteria inoculation
• Grantee: Antonio Marcos Miranda Silva
• Support Opportunities: Scholarships in Brazil - Doctorate