Brassica oleracea var. acephala is an important leafy vegetable that has been widely consumed as a high-nutrient, lowcalorie food. Because of the plant's biennial and self-incompatibility nature, biotechnological approaches are alternative way for propagation and breeding improvements. Since tissue culture studies have been focused in other B. oleracea representatives, the aim of the present study was to achieve effective regeneration protocol distinctive for collard greens, and evaluate the total phenolic content and antioxidant activity of regenerants. The effect of 3 cytokinins [thidiazuron (TDZ), 6-benzyladenine (BA) and 6-furfuryladenine (kinetin, KIN)] at increasing concentrations (0, 5, 7.5, 10, 20 or 30 µM) in combination with tenfold lower concentration of 1-naphtaleneacetic acid (NAA) (0, 0.5, 0.75, 1, 2 or 3 µM, respectively) on the regeneration from hypocotyl slices was studied. Histological analysis revealed the two regeneration pathways, somatic embryogenesis and shoot organogenesis, simultaneously occurred in the same explant, regardless of the cytokinin/NAA combinations used. The regeneration frequency of 95.9%, with 7.5 morphogenic structures regenerated per explant, and the healthy appearance of regenerated plants indicated the optimal combination 20 µM TDZ + 2 µM NAA. TDZ at 5 µM provided the high somatic embryo proliferation rate by generation of secondary embryos (7.79) along with the lowest rate of their abnormalities. Embryo-developed plants were successfully acclimatised (above 90%). The plants regenerated and proliferated on TDZ-containing media had higher total phenolic content that correlated with the highest free radical scavenging activity (IC 50 = 19.09 µg ml − 1 ). Key messageSomatic embryogenesis and shoot organogenesis from hypocotyl slices of the collard greens were established. The combination 20 µM TDZ + 2 µM NAA was optimal for regeneration providing higher total phenolic content.

Potential of Trichoderma harzianum IS005-12 (TH-IS005-12) to promote seed germination and seedling growth of Italian ryegrass (IRG) forage was evaluated in vitro. Non-desiccated seeds and those pre-harvestly desiccated with total herbicide were treated 25 days (freshly harvested) and 178 days after harvest (mature) with TH-IS005-12 spore suspensions at 0 (T0), 1.8 × 10⁷ (T1) and 1.2 × 10⁹ (T2) spore/mL. TH-IS005-12 promoted the early and final germination and seedling growth in all non-desiccated and desiccated, freshly harvested as well as mature IRG seeds. It was more effective in pre-harvestly desiccated freshly harvested seeds where T2 treatment increased final germination rate for 24%, root number per seedling 1.6-fold and seedling vigour 1.9-fold compared to the untreated control. Moreover, TH-IS005-12 showed an inhibitory activity against seedborne fungi Alternaria alternata and A. ventricosa suppressing their growth in vitro by 82% and 77%, respectively.

Seed treatments with zinc, boron, biostimulant Coveron and MIX (zinc + boron + Coveron) were applied to three lettuce and three celeriac cultivars. Seeds of three wheat cultivars were treated under laboratory conditions with Trichoderma harzianum and eight Bacillus spp. Seed germination, seedling growth, and the presence of the following pathogens were determined: Fusarium sp., Alternaria sp., Penicillium sp., and Mucor sp. The Coveron treatment was the most effective on lettuce seeds tested in the germination cabinet. Seed germination was higher by 4% than in the control. Alternatively, germination of seeds treated with boron in the greenhouse was higher by 12% than in the control. The Coveron treatment had the highest effect on the shoot length, which was greater by 0.7 and 2.1 cm in the germination cabinet and the greenhouse, respectively. This treatment was also the most effective on the root length. Zn, B, and MIX treatments increased celeriac seed germination by 14% in the germination cabinet. The Zn treatment was the most efficient on seeds tested in the greenhouse. The germination was higher by 15%. A significant cultivar × treatment interaction was determined in both observed species under both conditions. The maximum effect on wheat seed germination (8%) was achieved with the T. harzianum treatment in the Salazar cultivar. A significant interdependence (p ≤ 0.01 to p ≤ 0.001) was established between seed germination and the seedling growth. The interrelationship between seed germination and pathogens of all cultivars was negative.

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Apple species are the unique naturally rich source of dihydrochalcones, phenolic compounds with an elusive role in planta, but suggested auto-allelochemical features related to “apple replant disease” (ARD). Our aim was to elucidate the physiological basis of the phytotoxic action of dihydrochalcone phloretin in the model plant Arabidopsis and to promote phloretin as a new prospective eco-friendly phytotoxic compound. Phloretin treatment induced a significant dose-dependent growth retardation and severe morphological abnormalities and agravitropic behavior in Arabidopsis seedlings. Histological examination revealed a reduced starch content in the columella cells and a serious disturbance in root architecture, which resulted in the reduction in length of meristematic and elongation zones. Significantly disturbed auxin metabolome profile in roots with a particularly increased content of IAA accumulated in the lateral parts of the root apex, accompanied by changes in the expression of auxin biosynthetic and transport genes, especially PIN1, PIN3, PIN7, and ABCB1, indicates the role of auxin in physiological basis of phloretin-induced growth retardation. The results reveal a disturbance of auxin homeostasis as the main mechanism of phytotoxic action of phloretin. This mechanism makes phloretin a prospective candidate for an eco-friendly bioherbicide and paves the way for further research of phloretin role in ARD.

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