First report on cryopreservation of mature shoot tips of two avocado (Persea americana Mill.) rootstocks

Abstract

Cryopreservation combined with in vitro culture offers a safe and cost-effective method to conserve germplasm. Conservation of Persea spp. has been limited to heterozygous somatic embryos that are not true-to-type. A method for shoot-tip cryopreservation is vital to preserve the exact gene pool of interest. For the first time cryopreservation protocols for mature shoot tips of two avocado cultivars (cvs) ‘Velvick’ and ‘Reed’, were established. In vitro shoots were subjected to two different optimised pre-treatments; (1) cv ‘Velvick’—high sucrose (0.3 M) or (2) cv ‘Reed’—low temperature (10 °C) incubation, over a 2-week period prior shoot tip dissection. Two different plant vitrification solutions, plant vitrification solution 2 (PVS2) and vitrification solution L (VSL) were tested at 0 °C for 0, 10, 20, 30 and 40 min. Vitrified shoots were evaluated for survival and regrowth at 2 and 8 weeks after vitrification treatment and either with or without liquid nitrogen exposure. The study revealed that the optimal exposure time for each cultivar varied with the cryoprotectant used. After liquid nitrogen cv ‘Velvick’ highest regrowth levels were observed with 20 min exposure to either PVS2 or VSL, however, vigorous plants were produced only from VSL treated shoots. In the case of cv ‘Reed’ highest regrowth levels were observed with 10 min exposure to PVS2 however only morphologically normal plants were recovered from VSL treated shoots. Cryopreservation of avocado shoot tips was successful using PVS2 and VSL with both recording similar recovery rates for ‘Velvick’ and ‘Reed’; although only vigorous and morphologically normal plants were developed from VSL treatments.