Cryopreservation for Tree Species with Recalcitrant Seeds: the Avocado Case

Abstract

Recent developments in the cryopreservation space has increased the trend in germplasm collections established through cryopreserved in vitro material. Cryopreservation of recalcitrant seeds through embryos and embryonic axes, is not uncommon. Tropical and sub-tropical plants are not acclimated to the cold season, therefore have no in-built natural resilience to the cold. Also, larger seeds from trees, such as avocado (Persea americana Mill.), mango (Mangifera indica) and durian (Durio zibethinus L.) are sensitive to desiccation, chilling and freezing stress, making them unsuitable for seed banking or cryopreservation. Alternatively, as seeds do not carry the same genetic make-up as the mother plant, especially in the context of woody rainforest species of which the cross-pollination is dominant; seed conservation does not serve the purpose of germplasm preservation. Other plant material and methods are needed for these plants to be successfully stored in liquid nitrogen (LN). One such method commonly used is shoot-tip cryopreservation which ensures the clonal fidelity of germplasm. There are many problems when using shoot tips of tropical recalcitrant-seeded species. These include: 1) the toxic effects of cryoprotective agents towards structural integrity; 2) optimum developmental stage for success and 3) oxidative stress associated with excision injury leading to necrosis triggering cell death and hindering regeneration for the shoot tips in culture. A pre-requisite for any cryopreservation system is the availability of an established tissue culture regeneration platform. This review will outline conservation strategies for avocado with special emphasis on attempts and improvements made in the cryopreservation space for storing this horticulturally important crop ‘avocado’ at ultra-low temperatures.

The Effect of Antioxidants on Micropropagation of Avocado by Nodal Segments

“…The findings in the present study were similar to previously published results. In a study carried out by O'Brien et al (2020), it was reported that the survival rate in avocado increased in the media containing 100 and 250 mg L -1 AA. In the study conducted by Ahmad et al (2016), it was found that using AC, ASA and CA alone increased the survival rate in guava.…”

“…The results of this study were similar to some previous researches. In these studies, it has been reported that the application of AC, ASA, CA together to avocado explants gave better results than the application alone in terms of browning intensity (Nel et al, 1983;Pliego-Alfaro and Murashige, 1987;O'Brien et al, 2020).…”

“…In addition, different antioxidants have been used to reduce browning in avocado tissue culture medium. Several researchers have reported the addition of PVP (Dalsaso and Guevara, 1989;Ahmed et al, 2001;O'Brien et al, 2020) and melatonin (O'Brien et al, 2020) alone in the medium to control browning of cultured explants of avocado. Pre-treatment with different antioxidants is one of the ways to remove phenols or reduce the media browning (Krishna et al, 2008).…”

Sementes Recalcitrantes: Um Apanhado

“…armazenadas hidratadas e em câmara fria. Goldbach (1979) BARBEDO, 2014;DAVIES et al, 2018;STRECZYNSKI et al, 2019;BHARUTH & NAIDOO, 2020;O'BRIEN et al, 2020;BALLESTEROS et al, 2021).…”

“…O armazenamento de sementes geralmente oferece o mais seguro, eficiente e barato método de conservação, entretanto, para espécies que produzem sementes com alta recalcitrância o processo não é fácil e, muito menos simples (CORNIBEAU & CÔME, 1988). Razão pela qual houve, nas últimas décadas, forte incentivo à procura de métodos que ampliassem o período de armazenamento de tais sementes, e os menores avanços em técnicas de armazenamento, tão difíceis de se conseguir para essas espécies, foram e são de grande valia para os bancos de germoplasmas (BÖRNER & KHLESTKINA, 2019;BHARUTH & NAIDOO, 2020;O'BRIEN et al, 2020). Ainda assim, os resultados de muitas e aprofundadas pesquisas demonstram que, a única opção viável para a conservação a longo prazo de germoplasma de espécies produtoras de sementes recalcitrantes é a criopreservação (GONZALES-BENITO & PEREZ-RUIZ, 1992;HOR et al, 2005;WALTERS et al, 2013;PAMMENTER & BERJAK, 2014;DAVIES et al, 2018;STRECZYNSKI et al, 2019;BHARUTH & NAIDOO, 2020;O'BRIEN et al, 2020;BALLESTEROS et al, 2021).…”