Induced Genetic Variations in Fruit Trees Using New Breeding Tools: Food Security and Climate Resilience

CRISPR/Cas as a Genome-Editing Technique in Fruit Tree Breeding

CRISPR (short for "Clustered Regularly Interspaced Short Palindromic Repeats") is a technology that research scientists use to selectively modify the DNA of living organisms. CRISPR was adapted for use in the laboratory from the naturally occurring genome-editing systems found in bacteria. In this work, we reviewed the methods used to introduce CRISPR/Cas-mediated genome editing into fruit species, as well as the impacts of the application of this technology to activate and knock out target genes in different fruit tree species, including on tree development, yield, fruit quality, and tolerance to biotic and abiotic stresses. The application of this gene-editing technology could allow the development of new generations of fruit crops with improved traits by targeting different genetic segments or even could facilitate the introduction of traits into elite cultivars without changing other traits. However, currently, the scarcity of efficient regeneration and transformation protocols in some species, the fact that many of those procedures are genotype-dependent, and the convenience of segregating the transgenic parts of the CRISPR system represent the main handicaps limiting the potential of genetic editing techniques for fruit trees. Finally, the latest news on the legislation and regulations about the use of plants modified using CRISPR/Cas systems has been also discussed.

Spontaneous, Artificial, and Genome Editing-Mediated Mutations in Prunus

Mutation is a source of genetic diversity widely used in breeding programs for the acquisition of agronomically interesting characters in commercial varieties of the Prunus species, as well as in the rest of crop species. Mutation can occur in nature at a very low frequency or can be induced artificially. Spontaneous or bud sport mutations in somatic cells can be vegetatively propagated to get an individual with the mutant phenotype. Unlike animals, plants have unlimited growth and totipotent cells that let somatic mutations to be transmitted to the progeny. On the other hand, in vitro tissue culture makes it possible to induce mutation in plant material and perform large screenings for mutant’s selection and cleaning of chimeras. Finally, targeted mutagenesis has been boosted by the application of CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)/Cas9 and Transcription activator-like effector nuclease (TALEN) editing technologies. Over the last few decades, environmental stressors such as global warming have been threatening the supply of global demand for food based on population growth in the near future. For this purpose, the release of new varieties adapted to such changes is a requisite, and selected or generated Prunus mutants by properly regulated mechanisms could be helpful to this task. In this work, we reviewed the most relevant mutations for breeding traits in Prunus species such as flowering time, self-compatibility, fruit quality, and disease tolerance, including new molecular perspectives in the present postgenomic era including CRISPR/Cas9 and TALEN editing technologies.

Biotechnological Advances to Improve Abiotic Stress Tolerance in Crops

The major challenges that agriculture is facing in the twenty-first century are increasing droughts, water scarcity, flooding, poorer soils, and extreme temperatures due to climate change. However, most crops are not tolerant to extreme climatic environments. The aim in the near future, in a world with hunger and an increasing population, is to breed and/or engineer crops to tolerate abiotic stress with a higher yield. Some crop varieties display a certain degree of tolerance, which has been exploited by plant breeders to develop varieties that thrive under stress conditions. Moreover, a long list of genes involved in abiotic stress tolerance have been identified and characterized by molecular techniques and overexpressed individually in plant transformation experiments. Nevertheless, stress tolerance phenotypes are polygenetic traits, which current genomic tools are dissecting to exploit their use by accelerating genetic introgression using molecular markers or site-directed mutagenesis such as CRISPR-Cas9. In this review, we describe plant mechanisms to sense and tolerate adverse climate conditions and examine and discuss classic and new molecular tools to select and improve abiotic stress tolerance in major crops.

Characterization and Control of Thielaviopsis punctulata on Date Palm in Saudi Arabia

Date palm (Phoenix dactylifera L.) is the most important edible fruit crop in Saudi Arabia. Date palm cultivation and productivity are severely affected by various fungal diseases in date palm-producing countries. In recent years, black scorch disease has emerged as a devastating disease affecting date palm cultivation in the Arabian Peninsula. In the current survey, leaves and root samples were collected from deteriorated date palm trees showing variable symptoms of neck bending, leaf drying, tissue necrosis, wilting, and mortality of the entire tree in the Al-Ahsa region of Saudi Arabia. During microscopic examination, the fungus isolates growing on potato dextrose agar (PDA) media produced thick-walled chlamydospores and endoconidia. The morphological characterization confirmed the presence of Thielaviopsis punctulata in the date palm plant samples as the potential agent of black scorch disease. The results were further confirmed by polymerase chain reaction (PCR), sequencing, and phylogenetic dendrograms of partial regions of the ITS, TEF1-α, and β-tubulin genes. The nucleotide sequence comparison showed that the T. punctulata isolates were 99.9-100% identical to each other and to the T. punctulata isolate identified from Iraq-infecting date palm trees. The pathogenicity of the three selected T. punctulata isolates was also confirmed on date palm plants of Khalas cultivar. The morphological, molecular, and pathogenicity results confirmed that T. punctulata causes black scorch disease in symptomatic date palm plants in Saudi Arabia. Furthermore, seven commercially available fungicides were also tested for their potential efficacy to control black scorch disease. The in vitro application of the three fungicides Aliette, Score, and Tachigazole reduced the fungal growth zone by 86-100%, respectively, whereas the in vivo studies determined that the fungicides Aliette and Score significantly impeded the mycelial progression of T. punctulata with 40% and 73% efficiency, respectively. These fungicides can be used in integrated disease management (IDM) strategies to curb black scorch disease.