Abstract
Southern Spain is the largest olive oil producer region in the world. In recent years organic agriculture systems have grown exponentially so that new alternative systems to produce organic olive cuttings are needed. Several bacterial isolates, namely Pantoea sp. AG9, Chryseobacterium sp. AG13, Chryseobacterium sp. CT348, Pseudomonas sp. CT364 and Azospirillum brasilense Cd (ATCC 29729), have been used to induce rooting in olive semi-hardwood cuttings of Arbequina, Hojiblanca and Picual cultivars of olive (Olea europea L). The first four strains were previously selected as auxin-producing bacteria and by their ability to promote rooting in model plants. They have been classified on the basis of their 16S rDNA gene sequence. The known auxin producer A. brasilense Cd strain has been used as a reference. The inoculation of olive cuttings was performed in two different ways: (i) by dipping cuttings in a liquid bacterial culture or (ii) by immersing them in a paste made of solid bacterial inoculant and sterile water. Under nursery conditions all of the tested bacterial strains were able to induce the rooting of olive cuttings to a similar or greater extent than the control cuttings treated with indole-3-butyric acid (IBA). The olive cultivars responded differently depending on the bacterial strain and the inoculation method. The strain that consistently gave the best results was Pantoea sp. AG9, the only one of the tested bacterial strains to express the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase. The results are also discussed in terms of potential commercial interest and nursery feasibility performance of these strains.
Highlights
Synthetic chemical compounds used to prevent plant pest and disease symptoms or to fertilize plants can be detrimental to human health and they may persist in natural ecosystems (Glick et al, 2007; Pretty, 2008; Glick, 2010)
The inoculation of olive cuttings was performed in two different ways: (i) by dipping cuttings in a liquid bacterial culture or (ii) by immersing them in a paste made of solid bacterial inoculant and sterile water
Under nursery conditions all of the tested bacterial strains were able to induce the rooting of olive cuttings to a similar or greater extent than the control cuttings treated with indole-3-butyric acid (IBA)
Summary
Synthetic chemical compounds used to prevent plant pest and disease symptoms or to fertilize plants can be detrimental to human health and they may persist in natural ecosystems (Glick et al, 2007; Pretty, 2008; Glick, 2010). Free-living soil bacteria that provide some benefits to plants are often referred to as PGPR (plant growth promoting rhizobacteria) (Kloepper & Schroth, 1978) They may stimulate plant growth and development indirectly through their ability to prevent or decrease the damage to plants (Van Loon et al, 1998; Ramamoorthy et al, 2001) for example by synthesizing antibiotics that limit pathogen damage to plants or directly through biological activities as iron sequestration, phosphate solubilisation, the production of plant growth hormones such as indole-3-acetic acid (IAA), the most common auxin stimulating root elongation (Patten & Glick, 2002; Spaepen et al, 2007; Glick, 2010) or by lowering the growth-inhibiting levels of ethylene in plant tissues by production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase (Glick et al, 1998; Penrose et al, 2001; Toklikishvili et al, 2010)
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