Endophytic contaminants are a common problem for the in vitro propagation of woody plants and have significant economic repercussions for the conservation of plant genetic resources and commercial micropropagation. In this study, first, the microbial contamination that appeared around the base of in vitro-grown apple shoots was identified as Bacillus megaterium. Then, plant preservative mixture (PPMTM) was used as a bactericidal agent in plant tissue culture. Its efficacy for eradicating endophytic B. megaterium in in vitro cultures of apple was tested. In vitro-contaminated shoots were grown in tissue culture medium supplemented with 0.2% v/v PPMTM for 12 weeks and then transferred to medium without any PPMTM and cultured for 24 weeks. This study showed that PPMTM is an effective agent for controlling the growth of B. megaterium. Our results highlight the species-specific response of apple shoots to PPMTM. PPMTM was effective in controlling endogenous microbial contaminations from apple varieties ‘Golden Delicious’, ‘Landsberger Renette’, ‘Suislepper’, and ‘Aport krovavo-krasnyi’; meanwhile, in ‘KG 7’ and ‘Gold Rush’, all the plants grown in the absence of PPMTM were still bacterially contaminated, even though they were pre-treated for 12 weeks in PPMTM-supplemented medium. These results therefore suggest the essentiality of further testing of extended incubation of PPMTM in these cultivars that had outbreaks of bacterial contamination.

Studies carried out in Kazakhstan and abroad have shown the widespread prevalence of viral, bacterial and fungal diseases on apple commercial varieties and clonal rootstocks. Current paper presents the results on the viruses eradication from in vitro shoots of varieties and clonal rootstocks of apple (Malus domestica Borkh.) using chemotherapy and obtaining healthy super-elite planting stocks. Ribavirin at concentrations of 75 and 100 mg/L caused severe in vitro shoot necrosis. Three subcultures on Murashige-Skoog medium with 50 mg/L ribavirin was efficient for elimination of Apple chlorotic leaf spot virus (ACLSV), Apple stem pitting virus (ASPV), Apple stem grooving virus (ASGV), and Apple mosaic virus (ApMV) from in vitro shots of Malus varieties and clonal rootstocks. A virus-free in vitro collection (42 accessions) was established, which was used for create a cryobank of shoot tips at -196°C and to obtain virus-free planting stocks. The percentage of in vitro shoots rooting ranged from 50% to 90%. The survival rate of in vitro shoots rooted in the soil substrate is more than 90%.

The aim of this paper was to study the effect of plant growth regulators on callus induction and in vitro morphogenesis using various explants of Paulownia tomentosa to develop an efficient plant regeneration protocol. Different plant organ sections (leaves, apical shoot tips, petals, nodes, and internodes) were cultured as explants to identify the best in vitro explants responsive to callus induction and plant regeneration. Explants were cultivated on MS media supplemented with different concentrations of plant growth regulators (TDZ (Thidiazuron), BAP (6-Benzylaminopurine), kinetin, and NAA (1-Naphthaleneacetic acid). It was discovered that the addition of TDZ and NAA stimulated the induction of somatic embryogenesis. It was discovered that the MS medium with the combination of plant growth regulators BAP (35.5 µM) and NAA (5.4 µM) with the addition of 30.0 g/L maltose, 500.0 mg/L casein hydrolysate, and 250.0 mg/L L-proline was optimal for callus induction and multiple plant regeneration. The study of the regenerative capacity of various explants of Paulownia tomentosa in vitro showed that plant regeneration depends on the type of explant, and occurs in both ways, indirectly, through the formation of callus tissues and directly on the explant, without callus formation. As a result of this study, the efficient reproducible protocol of embryogenic callus formation and multiple shoot induction in vitro of Paulownia tomentosa was developed. This system provides a clear increase in the frequency of plant regeneration from 36.3 ± 3.4% to 38.6 ± 2.3% per embryogenic callus from leaves and apical shoot tips, respectively.

Печатается по постановлению Ученого совета ФГБУН «Ордена Трудового Красного Знамени Никитский ботанический сад-Национальный научный центр РАН» № 11 от «29» сентября 2020 г.