Effect of antioxidants and growth regulators on shoot organogenesis in the apical meristem culture of Fragaria × ananassa (Duchesne ex Weston) Duchesne ex Rozier

The initiation of strawberries into in vitro culture is known to be complicated by the inhibition of organogenesis by phenolic oxidation products. An important role in this process is given to the selection of growth regulators that increase meristematic cell activity and shoot proliferation at the stage of organogenesis induction. The present study aims to obtain a viable apical meristem culture of garden strawberry and to study the effect of different antioxidants (reduced glutathione (RG); a new preparation, i.e., a mechanical composite (MC) on the basis of biogenic silicon and green tea catechins and plant growth regulators (6-benzylaminopurine; thidiazuron) on the initiation of axillary shoot formation in strawberry meristem culture. Terminal buds containing an apical meristem and two leaf primordia isolated from the stolons of two garden strawberry cultivars (Sunny Meadow and Festival Chamomile) were used as primary explants for the initiation of strawberries into in vitro culture. It was found for the first time that the MC exhibits higher antioxidant activity as compared to reduced glutathione, reduces darkening of initial explants, as well as enhancing regeneration up to 13.0% at p ≤ 0.05. Furthermore, the best effect on the formation of microshoots per explant is observed toward the end of material introduction into in vitro culture when combining the MC with growth regulators in the culture medium. Here, the effect of strawberry cultivar on explant regeneration and the number of microshoots per explant are insignificant. It is concluded that the procedure for using the MC as an effective antioxidant during material initiation into the culture can be applied to the large-scale in vitro propagation of garden strawberries. Moreover, the technology for obtaining the MC from plant waste is environmentally friendly, which is a significant advantage for its use in in vitro technologies.

Spontaneous Regeneration of Plantlets Derived from Hairy Root Cultures of Lopezia racemosa and the Cytotoxic Activity of Their Organic Extracts

A histological analysis was performed with the aim of elucidating the spontaneous regeneration process of the hairy root lines LRT 2.3 and LRT 6.4, derived from Lopezia racemosa leaf explants and genetically transformed with the Agrobacterium rhizogenes strain ATCC15834/pTDT. The analysis showed both lines regenerate via indirect somatic embryogenesis; LRT 6.4 also regenerated by direct organogenesis. The morphogenic characteristics of the regenerated plantlets from both lines showed the typical characteristics, described previously, including a higher number of axillary shoot formation, short internodes, and plagiotropic roots compared with wild-type seedlings. The regeneration process occurred without the addition of plant growth regulators and was linked to the sucrose concentration in the culture medium. Reducing the sucrose concentration from 3% to 2%, 1%, and 0.5% increased the regeneration rate in LRT 6.4; the effect was less pronounced in LRT 2.3. The cytotoxic activity of different organic extracts obtained from roots and shoots were evaluated in the cancer cell lines HeLa (cervical carcinoma), HCT-15 (colon adenocarcinoma), and OVCAR (ovary carcinoma). The hexane and dichloromethane extracts from roots of both lines showed cytotoxic activity against the HeLa cell line. Only the dichloromethane extract from the roots of PLRT 2.3 showed cytotoxic activity against the OVCAR cell line. None of the methanol extracts showed cytotoxic activity, nor the shoot extracts from any solvent.

Endophytic Bacteria in Banana In Vitro Cultures: Molecular Identification, Antibiotic Susceptibility, and Plant Survival

Microbial contamination is a common problem that causes significant losses in plant micropropagation systems. The present study reports on the identification and control of bacterial contaminants in banana in vitro cultures. Twelve isolates belonging to Bacillus pumilus (S2), Bacillus subtilis (R2 and M4), Geobacillus stearothermophilus (S1, S3, S4, P2, M3 and R3) and Paenibacillus spp. (P1, R1 and M2) were identified by sequencing of 16S rRNA, gyrA or gyrB genes. Antibiotic susceptibility testing was performed with the disk diffusion method on bacterial isolates using 36 antimicrobial agents. Some antibiotics, notably Ticarcillin, Penicillin, Ampicillin, Cefazolin and Imipenem, had a broader range of bactericidal activity than others did. When contaminated axillary shoot cultures of banana were treated with 100 or 200 mg·L−1 of ticarcillin, ampicillin or penicillin the bacteria were eliminated, but a reduction in shoot multiplication and growth was observed. These findings contribute to minimizing the losses in the commercial micropropagation of banana.

Development of the first axillary in vitro shoot multiplication protocol for coconut palms

The coconut palm or “tree of life” is one of nature’s most useful plants and the demand for its fruit is increasing. However, coconut production is threatened by ageing plantations, pests and diseases. Currently, the palm is exclusively propagated via seeds, limiting the amount of planting material. A novel micropropagation method is presented, based on axillary shoot formation. Apical meristems of in vitro coconut seedlings are cultured onto Y3 medium containing 1 µM TDZ. This induces the apical meristem to proliferate through axillary shoots in ~ 27% of the initiated explants. These axillary shoots are seen as white clumps of proliferating tissue and can be multiplied at a large scale or regenerated into rooted in vitro plantlets. This innovative micropropagation method will enable the production of disease-free, high quality in vitro plantlets, which will solve the worldwide scarcity of coconut planting material.

Internodal Analysis of Avicennia marina in the Western Arabian Gulf

The growth of Avicennia marina (A. marina) was not previously assessed using internodal analysis in the Western Arabian Gulf. The node production in 40 branches/axillary shoot in Syhat city, Saudi Arabia, ranged from 6 to 9 nodes y–1. Moreover, the annual cycles of the internodal length represent the branch growth rate in centimeters per year (ranged from 12 to 43 cm; median of 19 cm) for minima to minima point and (from 15 to 46.5 cm; median of 25.5 cm) for maxima to maxima point. The results obtained in this study are fundamental for various applications, ranging from the planning of restoration and monitoring activities to reproduction estimates and establishing a useful baseline to assess responses to climate change via simple measurements. In particular, mangrove species are important as nurseries for many species for food and shelter, carbon sinks, and coastal protection.

Development of Micropropagation in Bigleaf Maple (Acer macrophyllum)

Natural populations of bigleaf maple (Acer macrophyllum Pursh) trees contain, at low frequency, individuals with stems that have attractive and valuable wavy grain in the wood. To maintain the genotype of these individuals, vegetative propagation is desired. To enable propagation from the limited amount of plant tissue that is often available, an in vitro micropropagation procedure was developed. A mix of wild trees was used as source material to generate a procedure that is genotype unspecific. Among tested basal media, DKW medium resulted in the highest frequency of growing shoots. For multiplication of shoots, removal of the apex of shoot explants was instrumental, presumably because this treatment broke a strong apical dominance in this species. Of tested hormone and hormone combinations, 0.1 μM thidiazuron produced the best results with an average of 3.2 axillary shoots per explant with an average of 3.7 nodes per axillary shoot after 1 month. Although rooting did not require hormone treatment, a 68% frequency of rooting was obtained on ½ MS supplemented with 1 μM IBA, 27% higher than hormone-free media. Taken together, we have developed a procedure for propagation of bigleaf maple from a limited amount of tissues that can be used to multiply various genotypes of interest.