**Preface**

Horticulture has established its importance in many aspects, including innovation, improving land use, promoting crop diversification, generating employment, and providing food to the world population. Thus, innovation in plant propagation and breeding is essential to meet the challenges of global changes such as population growth and climate change. Over the years, horticulturists have developed several propagation methods which have supported breeding programs and allowed the production of high-quality nursery plants and higher-yielding crops. Traditional breeding is one of the main strategies used to improve agronomic traits. In many horticultural species, several cultivars have been developed through conventional methods, such as mutagenesis, inter- and intra-specific crosses, and clonal selection. Conventional breeding is a long-term and expensive process; a long period of time and resources are needed to obtain progenies and to evaluate their traits. In addition, sexual breeding is not always feasible because some cultivars to be used in crosses are incompatible, sterile, or polyembryonic. Moreover, in many cases, after breeding, backcrosses are required to recover the desired features of the improved cultivar, further lengthening breeding programs. Since the 1990s, new biotechnology techniques have been applied to the propagation and breeding of horticultural species, providing efficient alternatives to traditional methods for the improvement of novel cultivars. This has been possible through the development of transformation protocols, starting from many sources of explants. More recently, several new techniques have been developed and classified as new plant breeding techniques.

> **Sergio Ruffo Roberto** *Editor*
