This Is AuburnElectronic Theses and Dissertations

Enhancing plant growth, drought stress tolerance, and biological control capacities of PGPR strains with exogenous pectin-rich amendments

Date

2020-06-15

Author

Hassan, Mohammad

Type of Degree

PhD Dissertation

Department

Entomology and Plant Pathology

Restriction Status

EMBARGOED

Restriction Type

Auburn University Users

Date Available

06-16-2021

Abstract

Bacillus velezensis is a plant growth-promoting rhizobacterium (PGPR) that promotes plant growth, enhances drought stress tolerance, and suppresses plant pathogens. However, little is known about the effects of exogenous pectin or orange peel amendments on plants by B. velezensis PGPR strains. The objectives of the present studies were: (i) to evaluate the combined effects of B. velezensis PGPR strains with exogenous pectin or orange peel amendments in soybean growth promotion and nodulation, (ii) to determine the capacity of B. velezensis PGPR strain with orange peel amendment to enhance drought stress tolerance in peanut (iii) to evaluate B. velezensis PGPR strain with orange peel amendment for their potential biological control of the southern root-knot nematode, Meloidogyne incognita in soybean and cotton. The treatments for objective one included soybean seeds planted in field soil that inoculated B. velezensis PGPR strains amended with or without exogenous pectin or orange peel and untreated control. The treatments for objective two included untreated peanut genotypes planted in field soil mixed with a potting mix that inoculated with B. velezensis PGPR strain amended with or without the orange peel. The treatments for objective three included soybean and cotton seeds planted in field soil that inoculated with cell pellet suspension, culture broth, and cell-free supernatant of B. velezensis PGPR strain grown in orange peel amended media and untreated control. In the greenhouse test, soybean seeds inoculated with B. velezensis PGPR strain AP193 and pectin had significantly increased shoot length, dry weight, and nodulation compared to the same strain without pectin amendment. Orange peel amendment in greenhouse test, with AP193 at 10 mg significantly increased the dry weight of shoots and roots compared to the same strain without pectin amendment. In the field test, pectin with B. velezensis PGPR strain AP193 significantly increased shoot length, dry weight, and nodulation compared to the same strain without pectin amendment. The biological control test results indicate that cell pellet suspension (CPS), culture broth (CB), and cell-free supernatant (CFS) of B. velezensis PGPR strain AP203 significantly reduced M. incognita population compared to M. incognita inoculated positive control at 45 days after planting (DAP) compared to M. incognita inoculated positive control in soybean and cotton. However, there were no significant differences between CPS, CB or CFS of B. velezensis strains grown in orange peel amended media. The specific leaf area (SLA), SPAD chlorophyll meter readings (SCMR), chlorophyll density (ChlD), and root length of B. velezensis strain AP203 with orange peel amendment were statistically significant compared to B. velezensis strain AP203 without orange peel amendment under drought stress tolerance conditions. Significant genotype x drought stress interactions were observed on most of the investigated agronomic traits. Genotype AU 18-33 of B. velezensis strain AP203 with orange peel amendment showed significant plant dry weight compared to B. velezensis strain AP203 without orange peel amendment under both water regimes. These results are significant as they illustrate the potential of B. velezensis PGPR strains to enhance soybean plant growth, peanut drought stress tolerance, and biological control of M. incognita by exogenous pectin or orange peel amendments.