Cryopreservation is considered an ideal strategy for the long-term preservation of plant genetic resources. Significant progress was achieved over the past several decades, resulting in the successful cryopreservation of the genetic resources of diverse plant species. Cryopreservation procedures often employ in vitro culture techniques and require the precise control of several steps, such as the excision of explants, preculture, osmo- and cryoprotection, dehydration, freeze-thaw cycle, unloading, and post-culture for the recovery of plants. These processes create a stressful environment and cause reactive oxygen species (ROS)-induced oxidative stress, which is detrimental to the growth and regeneration of tissues and plants from cryopreserved tissues. ROS-induced oxidative stresses were documented to induce (epi)genetic and somatic variations. Therefore, the development of true-to-type regenerants of the source germplasm is of primary concern in the application of plant cryopreservation technology. The present article provides a comprehensive assessment of epigenetic and genetic integrity, metabolic stability, and field performance of cryopreserved plants developed in the past decade. Potential areas and the directions of future research in plant cryopreservation are also proposed.

The estimated global production of raspberry from year 2016 to 2020 averaged 846,515 tons. The most common cultivated Rubus spp. is European red raspberry (Rubus idaeus L. subsp. idaeus). Often cultivated for its high nutritional value, the red raspberry (Rubus idaeus) is susceptible to multiple viruses that lead to yield loss. These viruses are transmitted through different mechanisms, of which one is invertebrate vectors. Aphids and nematodes are known to be vectors of specific raspberry viruses. However, there are still other potential raspberry virus vectors that are not well-studied. This review aimed to provide an overview of studies related to this topic. All the known invertebrates feeding on raspberry were summarized. Eight species of aphids and seven species of plant-parasitic nematodes were the only proven raspberry virus vectors. In addition, the eriophyid mite, Phyllocoptes gracilis, has been suggested as the natural vector of raspberry leaf blotch virus based on the current available evidence. Interactions between vector and non-vector herbivore may promote the spread of raspberry viruses. As a conclusion, there are still multiple aspects of this topic that require further studies to get a better understanding of the interactions among the viral pathogens, invertebrate vectors, and non-vectors in the raspberry agroecosystem. Eventually, this will assist in development of better pest management strategies.

In May 2021, tomato (Solanum lycopersicum L.) plants with necrosis and ringspot symptoms were observed in a farm greenhouse at Sundbyfoss, Norway. This greenhouse production focused on ecological growing of several tomato varieties (i.e., “Blush Tiger”, “Sailor’s Luck”, “Evil Oliver”, etc.) with compost for local customers. The presence of tomato brown rugose fruit virus (ToBRFV) was suspected due to the symptoms in the diseased plants. Sap inoculation was carried out with extracts from 100 mg symptomatic tomato fresh leaves in 0.03 M PBS (phosphate buffered saline, pH 7.0), and inoculation on three Nicotiana tabacum cv. Xanthi plants at the 4-6 leaf stage grown in an experimental greenhouse. The test plants showed local necrotic lesions after 3-5 days. Two symptomatic leaf samples, one from tomato and the other from a test plant, were analysed by transmission electron microscope (TEM) with the help of negative staining. The samples were treated with 0.1 M PBS (pH 7.3) first and placed on carbon-coated EM grids and stained with 2% uranyl acetate before TEM observation. Rigid rod-shaped viral particles, typical of tobamovirus particls (around 300 nm) were observed. Total RNA was isolated from two tomato leaves showing symptoms using a Norgen Plant/Fungi RNA kit (Norgen Biotek, Canada). One-step reverse-transcription (RT)-PCR with specific primers ToBRFV-F/ToBRFV-R for ToBRFV (Alkowni et al. 2019), which amplified a 560-bp fragment, was performed. The sequence obtained by Sanger sequencing from the amplicon (535 nt) showed 99.8% nt identity with ToBRFV isolate PV-1241 (NCBI accession no. MZ202349) from DSMZ (Leibniz Institute, German) and was deposited in the GenBank database under the accession number OK358628. The infection was also confirmed with duplex real-time RT-PCR test for ToBRFV using CaTa28 and CSP1325 primers and probe (ISF 2020; EPPO, PM7/146 2021). In addition, eight tomato samples from the same farm greenhouse were collected according to cultivars, location in the greenhouse and symptoms before eradication and disinfection: four of the tomato samples were confirmed positive for ToBRFV with one-step RT-PCR as described above. A surveillance program for ToBRFV in commercial greenhouse production has been carried out in 2021 in Norway. Around 4000 tomato plants from 18 commercial tomato growers were tested. No positive ToBRFV samples have been detected. However, unregulated tomato seeds from abroad and self-propagation of tomato by private gardeners and hobby growers is a potential threat to commercial production of tomato in Norway. To our knowledge, this is the first report of ToBRFV associated with tomato in Norway and in the Nordic countries.