Six examples of recalcitrant species.Photo of one whole and one split mango displaying its seed, which is approximately 1/3 the size of the entire fruit
Recalcitrant seeds areseeds that do not survive drying and freezing duringex situ conservation.[1] By and large, these seeds cannot resist the effects of drying or temperatures less than 10 °C (50 °F); thus, they cannot be stored for long periods likeorthodox seeds because they can lose their viability. Plants that produce recalcitrant seeds includeavocado,mango,mangosteen,lychee,cocoa,rubber tree, some horticultural trees,[2] aquatic plants such asNymphaea caerulea,[3] and several plants used in traditional medicine, such as species ofVirola andPentaclethra. Generally speaking, most tropicalpioneer species have orthodox seeds but manyclimax species have recalcitrant or intermediate seeds.[4]
The two main mechanisms causing damage to recalcitrant seeds aredesiccation effects on theintracellular structures and metabolic damage from the formation of toxic chemicals such asfree radicals.[5] An example of the first type of damage would be found in some recalcitrant nontropicalhardwood seeds, specifically theacorns of recalcitrantoaks, which can be stored in a non-frozen state for up to two years provided that precautions are taken against drying. These seeds show deterioration of cell membrane lipids and proteins after as few as 3–4 days of drying.[6] Other recalcitrant seeds, such as those of the sweet chestnut (Castanea sativa), show oxidative damage resulting from uncontrolled metabolism occurring during the drying process.[7]
Cryopreservation of the whole seed in an anti-freezing solution.[3]
Intermediate seeds are between orthodox and recalcitrant seeds in their survivability. They are initially identified by their inability to survive conventional dry-freezing storage while being able to survive cryopreservation as a whole. The storage guideline is to put them in refrigeration at 45–65% RH, for a maximum of five years.[8]
^Flores, E. M."Ch 1. Seed Biology". In Vozzo, J. A. (ed.).Tropical Tree Seed Manual. Forest Service, US Department of Agriculture.Archived from the original on 12 July 2017. Retrieved24 December 2011.
