دراسة تأثيرمتعدد السكر الخارجي المنتج من البكتريا المحفزة لنمو النبات في تخفيف الإجهاد المائي لنباتات الذرة الصفراء . Zea mays L

study of the effect of exopolysaccharide produced by the plant growth promoting bacteria in alleviation of water stress in Zea mays L. plants

Summary
The study was conducted in the graduate studies laboratory at the College of Science, University of Karbala, and in the Ministry of Technological Sciences – General Authority for Research, with the aim of preparing a bacterial vaccine from some bacterial species that promote plant growth bacteria (PGPB).
The study included two main axes:
The first axis: Isolating 60 local bacterial isolates from soils suffering from drought and water scarcity. It included a series of experiments to diagnose the isolates morphologically and microscopically. It diagnosed 20 bacterial isolates from the following genera: Bacillus, Pseudomonas, Azotobacter. It also studied the ability of these genera to produce extracellular polysaccharide. All isolates produced sugar in varying proportions. 10 isolates from each genera were selected, and the most productive of extracellular polysaccharide were selected.
A study of the tolerance of the most productive bacterial isolates to levels of drought induced using concentrations of (25, 20, 15, 10, 0)% of 600 (peg-600) Polyethylene glycol. It selected two isolates from each genera that were the most productive of extracellular polysaccharide and drought tolerance. Biochemical tests were performed on the six isolates selected in the study and the following were diagnosed:
(Bacillus subtilli, BreviBacillus Choshinenensi, Pseudomonas Putida, Pseudomonas Fluresense, Azotobacter chroococcum1, Azotobacter chroococcum2) and the diagnosis was confirmed using Vitek-2 and API20 for the first isolates.
Second axis: Using the six diagnosed isolates in alleviating drought stress through a series of the following experiments where yellow corn seeds were soaked. Zea mays L. was inoculated with the bacterial filtrate of the six isolates under study for 24 hours. A factorial experiment was carried out according to a RandomizedcompleteDesign (RC) design to study the effect of bacterial isolates in improving the tolerance of yellow corn seedlings to drought stress conditions induced by different irrigation periods every (24, 48, 72) hours. They were grown in Growth chambers under standard growth conditions of temperature and light intensity for 15 days. The results showed that: The use of bacterial isolates caused a significant increase in the drought tolerance index for unstressed yellow corn seedlings (irrigation every 24 hours) from 2.100 to 3.0), 2.3, 3.4, 2.3, 4.4, and stressed (irrigation every 48 hours) rose to (3.6, 3.1, 4.1, 2.4, 4.6) for each of the isolates Bacillus subtilis, BreviBacillus, Pseudomonas putida, Pseudomonas fluresense, Azotobacter chroococcum1, respectively.
The isolates significantly affected the increase in the chlorophyll content of the leaves, as it increased from 66.03 in the leaves of unstressed seedlings to (86.11, 82.20, 83.64, 80.69, 84.02⸲80.69) for the isolates Bacillus subtilis, BreviBacillus, Pseudomonas putida, Pseudomonas fluresense, Azotobacter1 chroococcum, Azotobacter chroococcum 2, respectively.
The isolates significantly affected the reduction in the severity of stress and the percentage of plasma membrane damage, and the percentage of decrease was recorded at 32% and 31.5% compared to the treatment with bacteria for the isolates Azotobacter1 chroococcum, Azotobacter chroococcum 2, respectively.
The isolates had a significant effect in increasing the soil moisture content and the highest moisture content of 33.070 was achieved by treatment with Bacillus subtilis.
Drought had a significant effect on most of the studied indicators and caused a significant increase in the stress intensity and the percentage of damage to the plasma membrane from (0.594) (41.991) respectively from non-stressed seedlings to (61.05) (0.937) in seedlings exposed to stress (irrigation every 72 hours) and a decrease in the seedling leaf content and chlorophyll stability from (80.438) to (67.447) and a decrease in the tolerance index from (2.7) to (2.41) and by a percentage of (9.7% and 8.93%) respectively.
The interaction between each of the bacterial isolates and the levels of drought had a significant effect on most of the studied characteristic.