Numerous environmental and endogenous factors affect the level of genetic diversity in natural populations. Genetic variability is the cornerstone of evolution and adaptation of species. However, currently, more and more plant species and local varieties (landraces) are on the brink of extinction due to anthropopression and climate change. Their preservation is imperative for the sake of future breeding programs. Gene banks have been created worldwide to conserve different plant species of cultural and economic importance. Many of them apply cryopreservation, a conservation method in which ultra-low temperatures (−135 °C to −196 °C) are used for long-term storage of tissue samples, with little risk of variation occurrence. Cells can be successfully cryopreserved in liquid nitrogen (LN) when the adverse effect of ice crystal formation and growth is mitigated by the removal of water and the formation of the so-called biological glass (vitrification). This state can be achieved in several ways. The involvement of key cold-regulated genes and proteins in the acquisition of cold tolerance in plant tissues may additionally improve the survival of LN-stored explants. The present review explains the importance of cryostorage in agronomy and presents an overview of the recent works accomplished with this strategy. The most widely used cryopreservation techniques, classic and modern cryoprotective agents, and some protocols applied in crops are considered to understand which parameters provide the establishment of high quality and broadly applicable cryopreservation. Attention is also focused on the issues of genetic integrity and functional genomics in plant cryobiology.

Horticultural crops comprise various economic species extending from fruits, nuts, vegetables, spices and condiments, ornamentals, aromatic, and medicinal plants. Ornamental and fruit plants are produced mainly for their nutritional and aesthetic values, respectively. Unfortunately, many tropical and subtropical species are in danger of extinction because of climate change and (a)biotic stresses. It is imperative to preserve the germplasms of these species for the present and future genetic improvement programs. Cryopreservation, i.e., maintenance of tissues at the ultralow temperature of liquid nitrogen, is a promising long-term preservation technique, alternative to seed or in vitro banks, which can be applied for both vegetatively and generatively (through seeds) propagated crops, including those with recalcitrant seeds. It is a technology of choice not only for the preservation of plant biodiversity but also for virus elimination in the proficient administration of large-scale micropropagation. The main advantages of cryopreservation are the lowering of in vitro culture expenditures, needed space, contamination risk, and operator errors. However, tropical species are temperature delicate and one of the foremost challenging issues is preconditioning treatments that stimulate physiological reactions to sufficiently enhance tolerance to dehydration and cryogenic procedures. In recent years, several cryopreservation methods based on encapsulation-vitrification, droplet-vitrification, the use of aluminum cryo-plates, and cryo-mesh have been established. Combined cryo-techniques, gene/DNA conservation, as well as studies on perceiving bio-molecular events and exploring the multistage process from the beginning to end of cryopreservation are receiving more emphasis. The development of cryobiomics delivers a conceptual framework to assess the significance of cell signaling mechanisms on cellular functions, the influence of cryoinjury factors on sample viability, and the implications for genetic stability following cryo-storage. The aim of this mini-review article is to provide a succinct synthesis of the developed cryogenic procedures and their use for the storage and exchange of genetic resources of tropical and subtropical horticultural crops, particularly fruit crops and ornamental plants under the threat of extinction.

The rice sheath blight disease, caused by Rhizoctonia solani J.G. Kühn fungus, is a major disease of Oryza sativa L. occurring all over the world. Therefore, efforts need to be undertaken to limit the spread of this pathogen, preferably by using environmentally friendly methods. In the present study, 57 fungal isolates were recovered by surface sterilization technique from 120 rice samples collected from paddy fields in Guilan province, Iran. Biological characterizations of the isolated taxa were performed in vitro, in the dual culture, volatile metabolites, and slide culture methods. Among the studied isolates, Trichoderma virens (J. H. Miller, Giddens and A. A. Foster) Arx was most effective in inhibiting the mycelial growth of R. solani in the dual culture (44.16% inhibition level), while Aspergillus fumigatus Fresen and T. virens had a 62.50–68.75% inhibition efficiency by volatile metabolites. In the slide culture, all of the isolates, except for T. harzianum Rifai, were effective in inhibiting the hyphae growth of R. solani. Under greenhouse conditions, rice plants inoculated with these potential antagonistic fungi showed a reduction in disease severity by even 41.4% as in the case of T. virens. Moreover, phenotypic properties of rice, such as plant height, fresh weight, and dry weight were increased in the plants inoculated with all antagonistic fungi tested, compared to the infected plants, except for the fresh weight of plants inoculated with Curnularia lunata (Wakker) Boedijn. The present in vivo and in vitro studies revealed that T. virens and A. fumigatus are the most effective antagonists in rice sheath blight disease control and could be applied in agricultural practice.

Peanut stem white rot caused by Sclerotium rolfsii Sacc. is a soil-borne disease that is widely prevailing across peanut farms, leading to serious economic losses. Screening for biocontrol agents against this pathogen is urgent. In this research, 166 fungal isolates including 136 isolates of S. rolfsii and 30 isolates of antagonistic endophytic fungi were obtained from a total of 220 samples collected from peanut farms in Guilan province, Iran. After morphological and molecular identification, six superior endophytic isolates were finally selected for the in vitro and greenhouse trials, including four isolates from Trichoderma viride, Trichoderma virens, Penicillium decaturense, and Aspergillus flavus and two isolates from Penicillium rubens. Four methods of biocontrol were used during the in vitro phase, i.e., dual culture, volatile metabolites assay, non-volatile metabolites assay (culture extract), and slide culture. It was found that T. virens had the highest capability of suppressing the mycelial growth of S. rolfsii in the dual culture method (90.98%). As for the volatile metabolites assay, the most effective isolates in inhibiting the pathogen’s mycelial growth were P. rubens (MN395854.1) and A. flavus (84.30% and 73.50% inhibition, respectively). In the non-volatile metabolites method, the isolates that performed the best in suppressing the mycelial growth of S. rolfsii were T. viride and P. rubens (MN395854.1) with 91.80% and 90.20% inhibitory effects, respectively. On the other hand, in the slide culture method, all isolates, except for T. virens and T. viride, successfully controlled the development of S. rolfsii hyphae. The greenhouse trials also supported the effectiveness of endophytic fungi in controlling the pathogen on the host plants. According to the results, T. viride, A. flavus, and P. rubens (MN395854.1) were 44%, 42%, and 38% effective in alleviating the disease incidence and severity. Moreover, the application of these antagonistic fungi in the greenhouse conditions increased the height, fresh weight, and dry weight of the Arachis hypogaea plants infected with the disease causal agent compared to the plants treated only with the pathogen. The results of the in vitro and greenhouse experiments revealed that the endophytic fungi occurring in the natural microbiota of peanut are capable of bio-controlling S. rolfsii, the causal agent of peanut stem white rot disease. These findings shed new insights into the possible resistance induction in A. hypogaea plants through biological protection.