Date of Defense
6-3-2025 2:00 PM
Location
F1-2007
Document Type
Thesis Defense
Degree Name
Master of Science in Molecular Biology and Biotechnology
College
COS
Department
Biology
First Advisor
Dr. Mayank Gururani
Keywords
Tomato, PGPR, Salinity, Stress, Photosynthesis, IAA
Abstract
Plant growth-promoting rhizobacteria (PGPRs) can effectively mitigate the negative impacts of salt stress on plants. The present study reports the isolation of PGPRs from a high-saline mangrove ecosystem in Abu Dhabi, with isolates exhibiting ACC deaminase (ACCD) activity to reduce stress-induced ethylene, along with additional plant growth-promoting (PGP) characteristics, including phosphate solubilization (P+). A total of 57 salt-tolerant bacterial isolates from the mangrove rhizosphere were initially screened for ACCD and P+ activities. Of these, 24 isolates tested positive for PGP characteristics and were further evaluated for their ability to enhance salt stress tolerance in tomato seedlings. In addition, seedlings inoculated with 9 selected isolates demonstrated improved growth compared to non-inoculated controls on agar plates containing 75 mM NaCl. Following additional screening, four isolates (B1–B4) were chosen for greenhouse experiments. Under greenhouse conditions, Bacillus subtilis (B1) and Bacillus siamensis (B3) were found to be more significant to alleviating salt stress-induced damage and enhancing salt tolerance in tomato plants, followed by Bacillus velezensis (B2), which showed a moderate effect. In contrast, Priestia filamentosa (B4) demonstrated the least impact of them all. Inoculation with B1 and B3 significantly increased shoot length, shoot dry weight (DW), shoot fresh weight (FW), root DW, root FW, and flower count per plant under saline conditions. In comparison, B2 exhibited a moderate effect, while B4 showed the least impact. Additionally, chlorophyll-a fluorescence studies showed that plants inoculated with B1 and B3 had the highest photosystem II (PSII) efficiency, followed by B2, while B4-treated plants showed the lowest efficiency under NaCl-induced salinity stress. Moreover, the leaf spectral reflectance indices of tomato plants inoculated with B1 and B3 were the highest, followed by moderate increases in B2-treated plants, while the lowest values were observed in plants treated with B4 and the uninoculated controls. The variation in salt tolerance among tomato plants treated with isolates B1–B4 was correlated quantitatively and qualitatively with the plant growth-promoting characteristics of the isolates, particularly their ACCD activity and IAA production. Overall, the findings suggest that isolates B1 and B3 hold the potential as biofertilizers to improve tomato production under saline conditions.
ASSESSMENT OF PHYSIOLOGICAL & BIOCHEMICAL CHANGES IN TOMATO PLANTS TREATED WITH PLANT GROWTH PROMOTING RHIZOBACTERIA (PGPR) UNDER SALINITY STRESS CONDITIONS
F1-2007
Plant growth-promoting rhizobacteria (PGPRs) can effectively mitigate the negative impacts of salt stress on plants. The present study reports the isolation of PGPRs from a high-saline mangrove ecosystem in Abu Dhabi, with isolates exhibiting ACC deaminase (ACCD) activity to reduce stress-induced ethylene, along with additional plant growth-promoting (PGP) characteristics, including phosphate solubilization (P+). A total of 57 salt-tolerant bacterial isolates from the mangrove rhizosphere were initially screened for ACCD and P+ activities. Of these, 24 isolates tested positive for PGP characteristics and were further evaluated for their ability to enhance salt stress tolerance in tomato seedlings. In addition, seedlings inoculated with 9 selected isolates demonstrated improved growth compared to non-inoculated controls on agar plates containing 75 mM NaCl. Following additional screening, four isolates (B1–B4) were chosen for greenhouse experiments. Under greenhouse conditions, Bacillus subtilis (B1) and Bacillus siamensis (B3) were found to be more significant to alleviating salt stress-induced damage and enhancing salt tolerance in tomato plants, followed by Bacillus velezensis (B2), which showed a moderate effect. In contrast, Priestia filamentosa (B4) demonstrated the least impact of them all. Inoculation with B1 and B3 significantly increased shoot length, shoot dry weight (DW), shoot fresh weight (FW), root DW, root FW, and flower count per plant under saline conditions. In comparison, B2 exhibited a moderate effect, while B4 showed the least impact. Additionally, chlorophyll-a fluorescence studies showed that plants inoculated with B1 and B3 had the highest photosystem II (PSII) efficiency, followed by B2, while B4-treated plants showed the lowest efficiency under NaCl-induced salinity stress. Moreover, the leaf spectral reflectance indices of tomato plants inoculated with B1 and B3 were the highest, followed by moderate increases in B2-treated plants, while the lowest values were observed in plants treated with B4 and the uninoculated controls. The variation in salt tolerance among tomato plants treated with isolates B1–B4 was correlated quantitatively and qualitatively with the plant growth-promoting characteristics of the isolates, particularly their ACCD activity and IAA production. Overall, the findings suggest that isolates B1 and B3 hold the potential as biofertilizers to improve tomato production under saline conditions.
