Androgenesis in recalcitrant solanaceous crops

Tomato, eggplant, and pepper are three solanaceous crops of outstanding importance worldwide. For hybrid seed production in these species, a fast and cheap method to obtain pure (homozygous) lines is a priority. Traditionally, pure lines are produced by classical inbreeding and selection techniques, which are time consuming (several years) and costly. Alternatively, it has become possible to accelerate the production of homozygous lines through a biotechnological approach: the induction of androgenesis to generate doubled haploid (homozygous) plants. This biotechnological in vitro tool reduces the process to only one generation, which implies important time and costs savings. These facts make androgenic doubled haploids the choice in a number of important crops where the methodology is well set up. Unfortunately, recalcitrant solanaceous crops such as tomato, eggplant, and pepper are still far from an efficient and reliable technology to be applied on a routine basis to different genotypes in breeding programs. In eggplant and pepper, only anther cultures are known to work relatively well. Unfortunately, a more efficient and promising technique, the culture of isolated microspores, is not sufficiently developed yet. In tomato, none of these methods is available nowadays. However, recent advances in the knowledge of embryo development are filling the gaps and opening new ways to achieve the final goal of an efficient protocol in these three recalcitrant species. In this review, we outline the state of the art on androgenic induction in tomato, eggplant, and pepper, and postulate new experimental ways in order to overcome current limitations.