Chitosan and silver nanoparticles are attractive auxin carriers: A comparative study on the adventitious rooting of microcuttings in apple rootstocks.

Nanocarriers for encapsulation and sustained release of agrochemicals such as auxins have emerged as an attractive strategy to provide enhanced bioavailability and efficacy for improved crop yields and nutrition quality. Here, a comparative study was conducted on the effectiveness of chitosan-as a biopolymeric nanocarrier- and silver-as a metallic nanocarrier- on in vitro adventitious rooting potential of microcuttings in apple rootstocks, for the first time. Auxins indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) loaded silver (nAg) or chitosan nanoparticles (nChi) were synthesized. Scanning electron microscopy and transmission electron microscopy studies showed the spherical shape of the nanoparticles. The average particle size of IAA-nChi was 167.5 ± 0.1 nm while that of IBA-nChi was 123.2 ± 2.6 nm. The hydrodynamic diameter of the nAg-IAA and nAg-IBA particles were measured as 93.66 ± 5 nm and 71.41 ± 3 nm, respectively. Fourier transform infrared spectroscopy analyses confirmed the encapsulation of IAA or IBA in the chitosan nanoparticles. Meanwhile, the characteristic peaks of IAA or IBA were detected on silver nanoparticles. In-vitro adventitious rooting of microcuttings of Malling Merton 106 (MM 106) was significantly higher both in chitosan and silver nanoparticles loaded with IAA or IBA (91.7%-62.5%) compared to free IAA or IBA applications (50.0%-33.3%), except for 2.0 mg L-1 IBA (66.7%). However, the application of 2 mg L-1 IBA and IBA-nChi at all concentrations caused an undesirable large callus development.

Synthesis of indole-3-acetic acid and indole-3-butyric acid loaded zinc oxide nanoparticles: Effects on rhizogenesis.

The aim of this work was to investigate the use of zinc oxide nanoparticles (nZnO) as nanocarriers for plant auxins indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) and determine the effects on rhizogenesis in micro cuttings of different Pyrus species. Auxin loaded nanoparticles (IAA-nZnO and IBA-nZnO) were characterized for particle size, morphology, thermal behavior and chemical structure. A high loading capacity was observed for both auxins (˜90%). Bioactivity assays were performed by using micro cuttings of Pyrus genotypes (Pyrus elaeagrifolia Pall and Pyrus communis L.) under aseptic conditions by dilute solution soaking method. In vitro rooting efficiency was increased at least two folds for the difficult-to-root wild pear (Pyrus elaeagrifolia Pallas) with IAA or IBA loaded ZnO nanoparticles. In this genotype, the highest rooting percentage was achieved for IBA-nZnO and IAA-nZnO at 400 mgL-1 concentration as 50.0% and 41.7%, respectively. Thus, auxin loaded ZnO nanoparticles could be used as efficient nanocarriers in agricultural applications.

In vitro shoot proliferation and in vitro and ex vitro root formation of Pyrus elaeagrifolia Pallas.

Shoot-tip cultures of Pyrus elaeagrifolia Pallas, an important gene source for drought and chlorosis resistance in pear rootstock breeding, were established from a wild mature tree originated from seed. Murashige and Skoog basal medium supplemented with different concentrations of benzyladenine (BA) singly or in combination with auxin was used in the study. In the initial culture, the highest percentages (>80%) of shoot proliferation were obtained in the mediums supplemented with 9.0 µM BA and 0.5 µM indole-3-acetic acid. In the subcultures, the highest shoot proliferation rates were obtained in the medium containing 4.5 and 9.0 µM BA. The shoot proliferation rates ranged from 91.1 ± 2.4 to 96.4 ± 2.0% in the second subculture and from 76.7 ± 7.8 to 89.4 ± 3.3% in the third subculture. In the second subculture, the shoots grown on 9.0 µM BA without auxin produced the best proliferation (10.6 ± 1.6). For the in vitro rooting experiments, the highest rooting rate (54.2 ± 10.4%), root length (10.5 ± 2.4 mm), and root number (2.5 ± 0.6) were obtained from 10 days dark treatment on the medium containing half strength of macronutrients supplemented with 5 µM indole-3-butyric acid (IBA). For the ex vitro rooting experiments, shoot rooting was significantly influenced by 10 mM IBA applied as quick-dip method. The percentage of rooting was 55 ± 9.6% and root number was 1.8 ± 0.3 at this concentration.