Anatomy and morphology of photinia (Photinia × fraseri Dress) in vitro plants inoculated with rhizobacteria

Abstract

Photinia 9 fraseri Dress (photinia) is a woody plant with high ornamental value. The anatomy and morphology of micropropagated photinia inoculated with the plant growth-promoting rhizobacteria Azospirillum brasilense and Azotobacter chroococcum, in combination with pulses of 49.2 lM indole-3-butyric acid during rhizogenesis, were characterized using light and electron microscopy. Leaves of inoculated in vitro plants showed better development than those subjected to auxin control only. All inoculated treatments, independent of the bacterial strain used, had leaves with two layers of palisade parenchyma, a thick cuticle and linear unicellular trichomes. There was no proliferation of undifferentiated tissue in any treatment and the plants showed shoot-root vascular connections. Ex vitro leaves and in vitro plants inoculated with Azospirillum brasilense Cd and Azotobacter chroococcum 42 had large stomata with elliptic aperture radially surrounded by small stomata on the abaxial foliar surface. In addition, plants of these treatments had a large root hair zone over the root surface. Bacteria were only observed on surfaces of root hairs. The results suggest that the structural changes induced by bacterial inoculation of photinia in vitro plants could lead to better adaptation to ex vitro conditions after transplanting.

Azospirillum brasilense enhances in vitro rhizogenesis of Handroanthus impetiginosus (pink lapacho) in different culture media

“…The IBA pulse concentration required to produce the maximum in vitro rooting percentage of H. impetiginosus shoots in both culture media was reduced by A. brasilense Cd and Az39 strain inoculation (Bashan and de-Bashan 2010). Similar effects were observed in jojoba, photinia, and soybean in vitro rooting (Carletti et al 1998;Larraburu et al 2007Larraburu et al , 2010Cassán et al 2009;Llorente and Larraburu 2013). The Cd strain also increased the pink lapacho rooting percentage without auxin induction, while the Az39 strain only stimulated H. impetiginosus induced with specific IBA concentrations.…”

“…They can colonize root surfaces as well as the root interior depending on the plant species, PGPR strains, and nutritional quality of the substrate (Bashan et al 2004). The allocation of A. brasilense Cd in H. impetiginosus was restricted to the root surface in accordance with that observed on photinia (Larraburu et al 2010). The bacteria formed microaggregates, and there were also fibrillar materials that could be associated with the exopolysaccharide secretion involved in bacterial aggregation and root surface colonization (Bashan et al 2004;Fibach-Paldi et al 2012).…”

“…The effect of different strains of Azospirillum brasilense on micropropagation has been studied in jojoba, photinia, soybean, and rootstocks of apple and plum (Carletti et al 1998;Larraburu et al 2007Larraburu et al , 2010Cassán et al 2009;Vettori et al 2010;Llorente and Larraburu 2013). These studies showed beneficial influences on rhizogenesis through growth promotion and fewer alterations during in vitro culture.…”

Engineering the Plant Microenvironment To Facilitate Plant-Growth-Promoting Microbe Association

“…This highlights that the root-dipping process is very time- and labor-intensive, which makes it unfeasible in large-scale agriculture . PGPB application performed on roots or cuttings to promote in vitro rhizogenesis is mainly performed in recalcitrant species. , They can be applied as a dipping solution or can be added to the rooting media just before transferring the shoots. , …”

“…127,128 They can be applied as a dipping solution or can be added to the rooting media just before transferring the shoots. 129,130 Exogenous application using foliar spraying is conducted using the inoculum alone or in specific formulations to ensure bacterial cell fixation on the leaves and also to maintain a live bacterial count until colonization through the stomatal apertures. 131 This method of application relies on climatic conditions; increased atmospheric temperature alters the plant microbe interaction by reducing the bacterial charge and inducing intrinsic reactions in the plant by water deficits.…”