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Colorado State University (2012)

The abundance of ACC deaminase-positive bacteria and their interaction with winter wheat in a Colorado soil

Abduelafez, Ibrahem

Titre : The abundance of ACC deaminase-positive bacteria and their interaction with winter wheat in a Colorado soil

Auteur : Abduelafez, Ibrahem

Université de soutenance : Colorado State University

Grade : Master of Science 2012

Résumé partiel
Plant growth-promoting rhizobacteria (PGPRs) are known as beneficial bacteria for plant growth and yield. One PGPR group are the ACC deaminase-positive (ACC+) bacteria which degrade 1-aminocyclopropane-1-carboxylic acid (ACC), the plant-produced precursor to ethylene. Plants produce ethylene in elevated quantities under environmental stress ("stress ethylene"), and studies have shown that ACC+ bacteria, in association with plant roots, can improve plant growth under abiotic stress (e.g., drought, salinity, heavy metals) by reducing concentrations of stress ethylene. There are few studies that have examined the natural abundance and distribution of these bacteria as affected by plant genotype, plant growth stage, and agricultural management practice ; and no studies have been conducted in the western United States. The objectives of my research were to determine the influence of winter wheat genotype and irrigation practice on the abundance of culturable ACC+ bacteria in a Colorado soil, and to determine the plant-growth-promoting effect of selected ACC+ on winter wheat varieties ranging in drought sensitivities under greenhouse conditions. A field study was conducted at the Limited Irrigation Research Farm (LIRF) in Greeley, Colorado. Roots and root-associated soil (0-20 cm depth) were collected with a shovel under four winter wheat varieties (Triticum aestivum L. "Baca", "Hatcher", "Ripper" and "RonL") managed by three different irrigation regimes : full irrigation, limited irrigation (irrigation commencing at the anthesis stage), and dryland. Samples were collected at four physiological growth stages during the 2010-2011 growing season : emergence (November 2010), green-up (March 2011), anthesis (May 2011) and mid-grain filling (June 2011). Total culturable bacteria were enumerated on TSB agar, and culturable ACC+ bacteria were enumerated on DF minimal salts agar media containing ACC as the sole N source. The abundance of ACC+ bacteria was relatively high in the Colorado soil (1.69 × 107- 3.28 × 109 CFU’s g-1) and varied according by an interaction between sampling date and irrigation practice

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