Phytotoxicity and Other Adverse Effects on the In Vitro Shoot Cultures Caused by Virus Elimination Treatments: Reasons and Solutions

The Elimination of Viroids through In Vitro Thermotherapy and a Meristem Tip Culture from a New Limonime Hybrid (Citrus x limon var. limon (L.) Burm. f. x Citrus latifolia var. latifolia)

Viruses and viroids pose a significant challenge in citriculture, and their control is crucial for plant health. This study evaluated the effectiveness of in vitro thermotherapy combined with a meristem tip culture for eliminating citrus exocortis viroid (CEVd) and hop stunt viroid (HSVd) from a new limonime hybrid (Citrus x limon var. limon x Citrus latifolia var. latifolia). The elimination success was confirmed by RT-PCR assays. The in vitro elimination rate for CEVd during the shoot proliferation stage (43%) was higher than for HSVd (21%). Accordingly, in the subsequent rooting stage, the in vitro elimination rate for CEVd (50%) was higher than for HSVd (33%). Successful CEVd and HSVd eradication at a 100% rate was confirmed in the ex vitro acclimatized plants in the greenhouse. The study also established an efficient micropropagation protocol. The optimal treatment for in vitro shoot induction was 0.5-2 mg L-1 benzyladenine (BA) + 0.5 mg L-1 gibberellic acid (GA3) + 0.25 mg L-1 naphthalene acetic acid (NAA), while for shoot elongation, it was 0.5 mg L-1 BA + 0.5 mg L-1 kinetin (KIN) + 0.5 mg L-1 GA3 + 0.25 mg L-1 NAA. Rooting was best promoted by 1 mg L-1 NAA. This study provides valuable insights for the mass production of viroid-free propagation material in this new lemon x lime hybrid, contributing to the conservation of genetic resources in citrus breeding programs through the combined application of in vitro thermotherapy and an in vitro meristem tip culture, a novel and highlighted achievement reported for the first time in this study.

Application of Biotechniques for In Vitro Virus and Viroid Elimination in Pome Fruit Crops

Sustainable production of pome fruit crops is dependent upon having virus-free planting materials. The production and distribution of plants derived from virus- and viroid-negative sources is necessary not only to control pome fruit viral diseases but also for sustainable breeding activities, as well as the safe movement of plant materials across borders. With variable success rates, different in vitro-based techniques, including shoot tip culture, micrografting, thermotherapy, chemotherapy, and shoot tip cryotherapy, have been employed to eliminate viruses from pome fruits. Higher pathogen eradication efficiencies have been achieved by combining two or more of these techniques. An accurate diagnosis that confirms complete viral elimination is crucial for developing effective management strategies. In recent years, considerable efforts have resulted in new reliable and efficient virus detection methods. This comprehensive review documents the development and recent advances in biotechnological methods that produce healthy pome fruit plants. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Considerations in engineering viral vectors for genome editing in plants

Plant viruses have been engineered to express proteins and induce gene silencing for decades. Recently, plant viruses have also been used to deliver components into plant cells for genome editing, a technique called virus-induced genome editing (VIGE). Although more than a dozen plant viruses have been engineered into VIGE vectors and VIGE has been successfully accomplished in some plant species, application of VIGE to crops that are difficult to tissue culture and/or have low regeneration efficiency is still tough. This paper discusses factors to consider for an ideal VIGE vector, including insertion capacity for foreign DNA, vertical transmission ability, expression level of the target gene, stability of foreign DNA insertion, and biosafety. We also proposed a step-by-step schedule for excavating the suitable viral vector for VIGE.

Comparative Analysis of Bioactive Compounds in Two Globe Artichoke Ecotypes Sanitized and Non-Sanitized from Viral Infections

Globe artichoke ecotypes sanitized from plant pathogen infections are characterized by high vegetative vigor, productivity, and quality of capitula. The recent availability on the market of these plants has renewed the interest of farmers and pharmaceutical industries in the crop. Globe artichoke exhibits interesting nutraceutical properties due to the high content of health-promoting bioactive compounds (BACs), such as polyphenols, that could be extracted from waste biomass. The production of BACs depends on several factors including the plant portion considered, the globe artichoke variety/ecotype, and the physiological status of the plants, linked to biotic and abiotic stresses. We investigated the influence of viral infections on polyphenol accumulation in two Apulian late-flowering ecotypes "Locale di Mola tardivo" and "Troianella", comparing sanitized virus-free material (S) vs. naturally virus-infected (non-sanitized, NS) plants. Transcriptome analysis of the two ecotypes highlighted that differentially expressed genes (DEGs), in the two tested conditions, were mainly involved in primary metabolism and processing of genetic/environmental information. The up-regulation of the genes related to the biosynthesis of secondary metabolites and the analysis of peroxidase activity suggested that their modulation is influenced by the phytosanitary status of the plant and is ecotype-dependent. Conversely, the phytochemical analysis showed a remarkable decrease in polyphenols and lignin accumulation in S artichokes compared to NS plants. This unique study analyzes the potential of growing vigorous, sanitized plants, in order to have high amounts of 'soft and clean' biomass, finalized for BAC extraction for nutraceutical purposes. This, in turn, opens new perspectives for a circular economy of sanitized artichokes, in line with the current phytosanitary standards and sustainable development goals.

Recovery of virus-free Almond (Prunus dulcis) cultivars by somatic embryogenesis from meristem undergone thermotherapy

One of the world's main horticulture problems is the contamination of fruit trees with a variety of plant diseases, especially viral and pseudo-viral diseases. Due to the non-sexual propagation of the trees, these diseases have been transmitted to different parts of the world. The main aim of this study was to obtain a new effective method for virus elimination from almond cultivars, which was performed in two phases. In the first phase, we tested various almond cultivars with ELISA and RT-PCR. The results showed the infection of mother plantlets. So, three types of in vitro thermotherapy treatments were performed on infected plants to make them virus-free. The plantlets obtained from 0.5 mm meristem treated with the first type of thermotherapy (TH1: 8 h at 27 °C and 16 h at 38 °C for 18 days) showed the highest percentage of elimination of ApM, ACLS and TRS viruses. In the second phase, meristems were cultured on MS medium containing 0, 0.5, 1 and 2 mg/L 2,4-D with 1 mg/L TDZ and after two weeks, thermotherapy treatments were performed. The results showed, combining three methods of thermotherapy (TH1), meristem culture and somatic embryogenesis induction from meristem on MS medium supplemented with 0.5 mg/L 2,4-D and 1 mg/L TDZ is the most effective and safe technique for virus eradication without meristem size challenges. The samples that were diagnosed as virus-free were proliferated in temporary immersion bioreactor systems, and rooted to be used for later propagation and establishment of mother healthy orchards.

An Effective Method of Ribes spp. Inoculation with Blackcurrant Reversion Virus under In Vitro Conditions

Blackcurrant reversion virus (BRV) is the most destructive currant-infecting and mite-transmitted pathogen from the genus Nepovirus. In this work, BRV transmission in the system Ribes ex vitro-Ribes in vitro was applied for the first time. Triple infection of BRV identified in blackcurrant cv. Gojai was used for phylogenetic analysis and inoculation assay. Transmission of BRV was successful due to its stability in the inoculum for up to 8 days at 4 °C; all BRV isolates were infectious. Our suggested inoculation method through roots was applied in six Ribes spp. genotypes with 100.0% reliability, and the expression levels of defence-related gene PR1 to biotic stress was observed. The prevalence of the virus in microshoots after 2-14 days post-inoculation (dpi) was established by PCR. In resistant genotypes, the BRV was identified up to 8 dpi; meanwhile, infection remained constant in susceptible genotypes. We established that BRV transmission under controlled conditions depends on the inoculum quality, post-inoculation cultivation temperature, and host-plant susceptibility to pathogen. This in vitro inoculation method opens possibilities to reveal the resistance mechanisms or response pathways to BRV and can be used for the selection of resistant Ribes spp. in breeding programs.

Eradication of Potato Virus S, Potato Virus A, and Potato Virus M From Infected in vitro-Grown Potato Shoots Using in vitro Therapies

Certain viruses dramatically affect yield and quality of potatoes and have proved difficult to eradicate with current approaches. Here, we describe a reliable and efficient virus eradication method that is high throughput and more efficacious at producing virus-free potato plants than current reported methods. Thermotherapy, chemotherapy, and cryotherapy treatments were tested alone and in combination for ability to eradicate single and mixed Potato virus S (PVS), Potato virus A (PVA), and Potato virus M (PVM) infections from three potato cultivars. Chemotherapy treatments were undertaken on in vitro shoot segments for four weeks in culture medium supplemented with 100 mg L^-1 ribavirin. Thermotherapy on in vitro shoot segments was applied for two weeks at 40°C (day) and 28°C (night) with a 16 h photoperiod. Plant vitrification solution 2 (PVS2) and cryotherapy treatments included a shoot tip preculture followed by exposure to PVS2 either without or with liquid nitrogen (LN, cryotherapy) treatment. The virus status of control and recovered plants following therapies was assessed in post-regeneration culture after 3 months and then retested in plants after they had been growing in a greenhouse for a further 3 months. Microtuber production was investigated using in vitro virus-free and virus-infected segments. We found that thermotherapy and cryotherapy (60 min PVS2 + LN) used alone were not effective in virus eradication, while chemotherapy was better but with variable efficacy (20-100%). The most effective result (70-100% virus eradication) was obtained by combining chemotherapy with cryotherapy, or by consecutive chemotherapy, combined chemotherapy and thermotherapy, then cryotherapy treatments irrespective of cultivar. Regrowth following the two best virus eradication treatments was similar ranging from 8.6 to 29% across the three cultivars. The importance of virus removal on yield was reflected in "Dunluce" free of PVS having higher numbers of microtubers and in "V500' free of PVS and PVA having a greater proportion of microtubers > 5 mm. Our improved procedure has potential for producing virus-free planting material for the potato industry. It could also underpin the global exchange of virus-free germplasm for conservation and breeding programs.

Thermotherapy Followed by Shoot Tip Cryotherapy Eradicates Latent Viruses and Apple Hammerhead Viroid from In Vitro Apple Rootstocks

Virus and viroid-free apple rootstocks are necessary for large-scale nursery propagation of apple (Malus domestica) trees. Apple stem grooving virus (ASGV) and Apple chlorotic leaf spot virus (ACLSV) are among the most serious apple viruses that are prevalent in most apple growing regions. In addition to these viruses, a new infectious agent named Apple hammerhead viroid (AHVd) has been identified. We investigated whether thermotherapy or cryotherapy alone or a combination of both could effectively eradicate ACLSV, ASGV, and AHVd from in vitro cultures of four apple rootstocks developed in the Cornell-Geneva apple rootstock breeding program (CG 2034, CG 4213, CG 5257, and CG 6006). For thermotherapy treatments, in vitro plants were treated for four weeks at 36 °C (day) and 32 °C (night). Plant vitrification solution 2 (PVS2) and cryotherapy treatments included a shoot tip preculture in 2 M glycerol + 0.8 M sucrose for one day followed by exposure to PVS2 for 60 or 75 min at 22 °C, either without or with liquid nitrogen (LN, cryotherapy) exposure. Combinations of thermotherapy and PVS2/cryotherapy treatments were also performed. Following treatments, shoot tips were warmed, recovered on growth medium, transferred to the greenhouse, grown, placed in dormancy inducing conditions, and then grown again prior to sampling leaves for the presence of viruses and viroids. Overall, thermotherapy combined with cryotherapy treatment resulted in the highest percentage of virus- and viroid-free plants, suggesting great potential for producing virus- and viroid-free planting materials for the apple industry. Furthermore, it could also be a valuable tool to support the global exchange of apple germplasm.