Old and new horizons on Persea americana transformation techniques and applications

The avocado, Persea americana Mill., is one of the most traded tropical fruits in the international market, furthermore, demand has significantly grown over the last decade, increasing its prices and expanding its production. In the current scenario of increasing concern about environmental impact due to the expansion of avocado orchards, climate change and epidemics of invasive pathogens, there is a need to accelerate avocado breeding programmes. Developing new avocado cultivars with novel traits is an important goal for breeders, all in a time- and cost-efficient manner. Desirable traits include the development of dwarf rootstocks, increased postharvest shelf life, salinity, and drought stress tolerance as well as resistance to major pathogens such as Phytophthora cinnamomi , Rosellinia necatrix , and Raffaelea lauricola . At the same time, genetic improvements done in avocado by the agency of traditional breeding have been moderately successful, which is why even today main cultivars still come from seedlings from open pollination. However, advancements on molecular biology and genetic engineering techniques have expanded knowledge on breeding different plants, including some perennial species, in a more efficient, precise, and targeted manner. This review summarises the available literature on avocado genetic transformation works, focusing on the methodologies, highlighting achievements and challenges.