Early embryo achievement through isolated microspore culture in Citrus clementina Hort. ex Tan., cvs. 'Monreal Rosso' and 'Nules'

Seed germination and vegetative and in vitro propagation of Hieracium lucidum subsp. lucidum (Asteraceae), a critically endangered endemic taxon of the Sicilian flora

Hieracium lucidum subsp. lucidum is a critically endangered endemic taxa of the Sicilian flora. It is a relict of the Tertiary period surviving on the cliffs of Monte Gallo (NW-Sicily). This research focused on finding the best protocols for seed germination and vegetative and in vitro propagation to contribute to ex situ conservation. Seed germination tests were carried out using constant temperatures of 15 °C, 20 °C and 25 °C in continuous darkness and an alternating temperature of 30/15 °C (16 h/8 h, light/dark). The seeds had no dormancy, and a high germination capacity (70-95%) was obtained at all tested thermoperiods. The possibility of vegetative propagation of the taxon was evaluated through the rooting capacity of stem cuttings treated or not treated with indole-3-butyric acid (IBA). All cuttings were treated with IBA rooted within 2 months, while only 50% of the untreated cuttings were rooted within a longer time. An efficient protocol for rapid in vitro propagation from leaf portions was developed. The response of explants was tested on hormone-free Murashige and Skoog (MS) basal medium and MS enriched with different types of cytokinins: 6-Benzylaminopurine (BAP) and meta-Topolin (mT) in combination with naphthaleneacetic acid (NAA) and 2,4-Dichlorophenoxyacetic acid (2,4-D) at the same concentration. The combination of mT (2 mg L-1) and 2,4-D (1 mg L-1) in the medium was the most effective and showed the highest percentage of callus induction and the mean number of regenerated shoots. The maximum rate of root regeneration and the maximum number and length of roots were obtained on hormone-free MS and MS enriched with IBA at concentrations of 1 mg L-1. From the results obtained, it can be concluded that H. lucidum subsp. lucidum can be successfully propagated using one of the tested techniques, subject to the availability of the material for reproduction.

Anther Culture-Derived Haploids of Citrus aurantium L. (Sour Orange) and Genetic Verification of Haploid-Derived Regenerated Plants

Citrus plants are important fruit tree species; however, the breeding of high-quality varieties of citrus species is a time-consuming process. Using haploid-derived plants from anther culture may reduce the time required for obtaining purebred lines. This study aimed to genetically verify whether anther culture-derived sour orange (Citrus aurantium L.) plants developed from somatic embryos or haploid tissues. Sour orange anthers were cultured in N6 and MS media to induce calli and somatic embryos. N6 liquid medium supplemented with 1 mg·L^-1 gibberellic acid and 200 µM spermidine resulted in a 10% increase in callus and embryo induction rates. Regenerated plants were validated using simple sequence repeat markers. Out of the 109 regenerated plants, ploidy analysis identified 99 diploids, two haploids, and eight putative aneuploids; out of the 99 diploid plants, 33 were haploid-derived homozygous diploids. The chromosomal analysis confirmed most plants as diploids, whereas some were identified as aneuploids (19-21 chromosomes). Furthermore, phylogenetic analysis confirmed that the resultant homozygous or heterozygous plants were haploid-derived. This is the first report of haploid-derived homozygous diploid and aneuploid sour orange plants obtained through anther culture. Moreover, the anther cultivation technique described herein can be applied to other citrus varieties.

Species with Haploid or Doubled Haploid Protocols

In this chapter, we present a list of species (and few interspecific hybrids) where haploids and/or doubled haploids have been published, including the method by which they were obtained and the corresponding references. This list is an update of the compilation work of Maluszynski et al. published in 2003, including new species for which protocols were not available at that time, and also novel methodologies developed during these years. The list includes 383 different backgrounds. In this book, we present full protocols to produce DHs in 43 of the species included in this list. In addition, this book includes a chapter for one species not included in the list. This makes a total of 384 species where haploids and/or DHs have been reported up to date.

In Vitro Regeneration of Capparis spinosa L. by Using a Temporary Immersion System

Three caper (Capparis spinosa L.) biotypes grown on the Sicilian island of Salina (38°33′49″ N) were micropropagated to evaluate two different in vitro culture systems: one using the traditional solid medium, and the other based on liquid culture in a PlantForm bioreactor. PlantForm is a temporary immersion system (TIS), a new propagation method in which the shoots undergo temporary immersion in a liquid medium in order to avoid the accumulation of gas through forced ventilation. This study proposes a protocol to improve the efficiency of in vitro propagation of caper plants, while also reducing production costs, because of the elimination of the gelling agent, and manual labor, requiring limited subcultures and posing minimal contamination risks. Our results show that the caper shoots propagated in bioreactors demonstrated good adaptability and better growth rates than those grown in the conventional system. Statistically significant differences were observed between plants grown in the PlantForm liquid culture and those grown in solid medium regarding the number and length of shoots, which were further promoted by the addition of plant growth regulators (PGRs). The relative growth and real proliferation rate of the caper explants were higher when using meta-Topolin than when using 6-benzylaminopurine as a PGR. Overall, the TIS improved in vitro caper culture by promoting the proliferation, length, and vigor of the shoots.

Microspore embryogenesis: targeting the determinant factors of stress-induced cell reprogramming for crop improvement

Under stress, isolated microspores are reprogrammed in vitro towards embryogenesis, producing doubled haploid plants that are useful biotechnological tools in plant breeding as a source of new genetic variability, fixed in homozygous plants in only one generation. Stress-induced cell death and low rates of cell reprogramming are major factors that reduce yield. Knowledge gained in recent years has revealed that initiation and progression of microspore embryogenesis involve a complex network of factors, whose roles are not yet well understood. Here, I review recent findings on the determinant factors underlying stress-induced microspore embryogenesis, focusing on the role of autophagy, cell death, auxin, chromatin modifications, and the cell wall. Autophagy and cell death proteases are crucial players in the response to stress, while cell reprogramming and acquisition of totipotency are regulated by hormonal and epigenetic mechanisms. Auxin biosynthesis, transport, and action are required for microspore embryogenesis. Initial stages involve DNA hypomethylation, H3K9 demethylation, and H3/H4 acetylation. Cell wall remodelling, with pectin de-methylesterification and arabinogalactan protein expression, is necessary for embryo development. Recent reports show that treatments with small modulators of autophagy, proteases, and epigenetic marks reduce cell death and enhance embryogenesis initiation in several crops, opening up new possibilities for improving in vitro embryo production in breeding programmes.

Micropropagation in the Twenty-First Century

Despite more than a century of research on effective biotechnological methods, micropropagation continues to be an important tool for the large-scale production of clonal plantlets of several important plant species that retain genetic fidelity and are pest-free. In some cases, micropropagation is the only technique that supports the maintenance and promotes the economic value of specific agricultural species. The micropropagation of plants solved many phytosanitary problems and allowed both the expansion and access to high-quality plants for growers from different countries and economic backgrounds, thereby effectively contributing to an agricultural expansion in this and the last century. The challenges for micropropagation in the twenty-first century include cost reduction, enhanced efficiency, developing new technologies, and combining micropropagation with other systems/propagation techniques such as microcuttings, hydroponics, and aeroponics. In this chapter, we discuss the actual uses of micropropagation in this century, its importance and limitations, and some possible techniques that can effectively increase its wider application by replacing certain conventional techniques and technologies.