In vitro root induction and growth of Lens esculenta and Physalis ixocarpa shoot explants by plant growth promoting rhizobacteria

As some authors noted [1-4], PGPR (Plant Growth Promoting Rhizobacteria) have gained worldwide importance and acceptance. Mechanisms involved in plant growth promotion by PGPR’s produce direct and indirect effects; one of those direct effects is the production of phytohormones. Ramos-Solano et al. [5] mentioned that the modification of a plant’s physiology by plant growth regulator production is a very important mechanism, not only because it alters the principal mechanism of plant growth regulation but also because it is based on the evolutionary development of common metabolic pathways in plants and bacteria. Glick et al. [6] showed that the promotion of root growth is one of the major markers by which the beneficial effect of plant growth-promoting bacteria is measured; it is related to rapid establishment of roots that is advantageous for young seedlings to obtain water and nutrients from their environment [7]. Recent studies confirm that the treatments of seeds or cuttings inoculated with these kind of beneficial microorganisms such as Agrobacterium, Alcaligenes, Azospirillum, Azotobacter, Bacillus, Pseudomonas and Streptomyces, reported the effect on rhizogenesis, growth promotion and reduction of hyperhydricity of in vitro cultured plants [8-14]; that induce root formation because of natural auxin production by these bacteria [4, 15, 16]. Although the mechanisms are not completely understood, root induction by PGPR’s is the accepted result of auxin production [17]. Microbial production of the auxin indole-3-acetic acid (IAA) has been extensively reported [18,19]. Most studies using microorganisms that produce IAA have reported a link between IAA production and root development and morphology [20,21]. Many different bacterial species can produce IAA through various mechanisms. Aeromonas spp., Azospirillum brasilense and Comamonas acidovorans are among the many IAA species that promote plant growth in rice [22], wheat [23] and lettuce [24]. Kapulnik et al. [25] and Lifshitz et al. [26], reported that considering the numerous interactions between the different hormonal signaling pathways in plants, it is difficult to assess which of these pathways is the primary target of PGPR’s, but it is known that these microorganisms modify phytohormonal pathways by the different morphological changes observed, like the lateral root elongation and root hair development. One of the more characteristic effects of PGPR’s is the increased elongation and initiation rate of lateral roots, giving a more branched root system. These authors finally mention that the employ of PGPR’s for nursery material multiplication may be important for obtaining organic nursery material. Nowak and Shulaev [27], Vestberg et al. [28] and Larraburu et al. [29] reported that the inoculation with PGPR’s in tissue culture eliminate many of the difficulties associated with the rooting of stem cuttings and protect the micropropagated plants against biotic and abiotic stress. 

The aim of this work was to analyze the effects of the auxin rhizobacteria producer Pseudomonas sp. strain C2 on in vitro rooting and shoot elongation of Lens esculenta and Physalis ixocarpa stem cuttings.