Cuban rice cultivars INCA LP-5 and INCA LP-7 are widely distributed in Cuba and Caribbean countries. Although there are studies about rhizospheric bacteria associated with these cultivars, there are no reports about their seed-associated bacteria. This study aimed to isolate endophytic bacteria from rice seeds and select those with the greatest plant growth-promoting traits. A total of nineteen bacterial strains from the genera Pantoea, Bacillus, Paenibacillus, and Pseudomonas were isolated from the husk and endosperm of rice seeds. The strains Pantoea sp. S5-1, Pseudomonas sp. S5-38, and Pseudomonas sp. S7-1 were classified as the most promissory to increase rice growth as they demonstrated the presence of multiple plant growth-promoting traits such as the production of auxins, phosphate, and potassium solubilization, the production of siderophores, and the inhibition of the phytopathogen Pyricularia oryzae. The inoculation of strains of Pantoea sp. and Pseudomonas spp. in rice improves the height, root length, fresh weight, and dry weight of the shoot and root after 21 days post-inoculation in hydroponic assays. This study constitutes the first report on Cuban rice cultivars about the presence of endophytes in seeds and their potential to promote seedling growth. Pantoea sp. S5-1, Pseudomonas sp. S5-38, and Pseudomonas sp. S7-1 were selected as the more promising strains for the development of bio-stimulators or bio-inoculants for Cuban rice crops.

In the present study, a high yield of isolated protoplasts from the agronomically important crop Fagopyrum esculentum was obtained by applying a mixture of cellulase, pectolyase, and driselase. We demonstrated that the yield of morphogenic callus-derived protoplasts was 1 × 10⁶ protoplasts per g of fresh tissue. For hypocotyls used as the protoplast source, the number of released cells was twice lower. The protoplasts, embedded in an agarose matrix and cultured in a modified Kao and Michayluk media supplemented with phytosulfokine, re-enter the cell cycle and start to develop, forming microcalli. The plating efficiency was about 20% in the case of hypocotyl- and morphogenic callus-derived protoplasts. For plant regeneration, the medium was supplemented with different combinations of cytokinin. Somatic embryogenesis and organogenesis occur during the cultivation of the protoplast-derived tissues, depending on the applied protoplast source. For the first time, an effective protoplast-to-plant system for F. esculentum has been developed.

Background: Fagopyrum tataricum (Tartary buckwheat) is a valuable crop of great nutritional importance due to its high level of bioactive compounds. Excellent opportunities to obtain plants with the high level or the desired profile of valuable metabolites may be provided by in vitro cultures. Among known in vitro techniques, protoplast technology is an exciting tool for genetic manipulation to improve crop traits. In that context, protoplast fusion may be applied to generate hybrid cells between different species of Fagopyrum. To apply protoplast cultures to the aforementioned approaches in this research, we established the protoplast-to-plant system in Tartary buckwheat. Results: In this work, cellulase and pectinase activity enabled protoplast isolation from non-morphogenic and morphogenic callus (MC), reaching, on average, 2.3 × 10⁶ protoplasts per g of fresh weight. However, to release protoplasts from hypocotyls, the key step was the application of driselase in the enzyme mixture. We showed that colony formation could be induced after protoplast embedding in agarose compared to the alginate matrix. Protoplasts cultured in a medium based on Kao and Michayluk supplemented with phytosulfokine (PSK) rebuilt cell walls, underwent repeated mitotic division, formed aggregates, which consequently led to callus formation. Plating efficiency, expressing the number of cell aggregate formed, in 10-day-old protoplast cultures varied from 14% for morphogenic callus to 30% for hypocotyls used as a protoplast source. However plant regeneration via somatic embryogenesis and organogenesis occurred only during the cultivation of MC-derived protoplasts. Conclusions: This study demonstrated that the applied protoplast isolation approach facilitated the recovery of viable protoplasts. Moreover, the embedding of protoplasts in an agarose matrix and supplementation of a culture medium with PSK effectively stimulated cell division and further development of Tartary buckwheat protoplast cultures along with the plant regeneration. Together, these results provide the first evidence of developing a protoplast-to-plant system from the MC of Fagopyrum tataricum used as source material. These findings suggest that Tartary buckwheat’s protoplast cultures have potential implications for the species’ somatic hybridization and genetic improvement.

Background: Fagopyrum tataricum (Tartary buckwheat) is known for its high phenolic content, particularly rutin. High concentrations of these compounds secreted in the tissue culture medium can lead to its darkening and the eventual death of explants in in vitro cultures. This study aims to enhance the morphogenesis of F. tataricum callus cultures by utilising phenylalanine ammonia-lyase (PAL) inhibitors and polyvinylpyrrolidone (PVP) to mitigate oxidative browning and improve tissue viability. Results: We analysed the response of protoplasts isolated from morphogenic callus to media supplemented with varying concentrations of PAL inhibitors (AIP, AOPP, OBHA) and PVP. The flow cytometry results revealed that 10 µM AIP and 1% PVP yielded exclusively diploid plants, whereas higher concentrations (100 µM AIP and 3% PVP) failed to regenerate plants. Moreover, AOPP and OBHA addition resulted in the regeneration of tetraploid plants. Further analysis of proembryogenic cell complexes (PECCs) isolated from Tartary buckwheat morphogenic calli responses to AIP and PVP indicated that 100 µM AIP was most effective for plant regeneration. Metabolomic analysis showed that AIP treatments reduced phenolic compounds, notably rutin, and increased the GSH/GSSG ratio, indicating reduced oxidative stress. Gene expression analysis highlighted elevated expression of somatic embryogenesis-related genes (LEC2, BBM) and WUSCHEL in AIP-treated callus. Conclusions: This study demonstrates that AIP enhances the regeneration potential of F. tataricum callus cultures, offering valuable insights for optimising tissue culture techniques for industrial crops. Additionally, we have detailed the metabolomic changes in calli treated with PVP and AIP, highlighting their impact on metabolism. Graphical

Potassium is one of the most important elements in plant growth and development. Most of the potassium reserves on Earth are in insoluble mineral form, which represents a limitation for the absorption of this nutrient by plants. Some microorganisms can solubilize the mineral forms of potassium. This study aimed to isolate and identify potassium solubilizing bacteria resident in corn rhizoplane. To do this, bacteria that formed a solubilization halo around the colony on solid Aleksandrov culture medium were selected. These bacteria were then characterized considering the appearance of the colonies and cell morphology and were identified by partial 16S rDNA sequencing. Their solubilizing and potassium-releasing capacity was determined under different conditions of temperature, pH, and salinity, using potassium feldspar and muscovite as insoluble sources of potassium. Eight strains identified within the genera Paenibacillus, Lysinibacillus, Arthrobacter, Bacillus, Pseudomonas, and Stenotrophomonas were obtained. The release of potassium from feldspar was favored at 28 and 30°C, pH 7.5 and a saline concentration of 4 g L-1, while in the presence of muscovite the best conditions were 30 and 37°C, pH 5.5 and 7.5, and 4 g L-1 of NaCl. The most efficient strains were Bacillus sp. INCA-FRc7 and Bacillus sp. INCA-FRc19x with yields of up to 2.095 mg L-1. These strains could become alternatives to the use of potassium fertilizers and contribute to the ecological sanitation of the agroecosystems.