In vitro germination protocol for the propagation of the endangered butternut tree (Juglans cinerea L.)

Abstract

Butternut (Juglans cinerea L. [Juglandaceae]) is a native tree in the US and Canada that is in rapid decline due to an introduced fungal pathogen (Ophiognomonia clavigignenti juglandacearum [Oc-j]). Resistance to the disease has not been identified, and conservation efforts for this nut-producing species have concentrated on the ex situ cryogenic storage of germplasm. The conventional method for growing butternut uses the nut. In general, Juglans species exhibit seed dormancy, which can be broken by cold, moist stratification at 1–4 °C (32–39.2 °F) for 90–120 d. Stratified nuts usually germinate within 4 wk, with variation among seeds. Average germination by the conventional method is approximately 60% for J. cinerea. A new in vitro germination protocol has been developed for the production of butternut seedlings that results in high germination and acclimatization success (conversion of germinants growing on medium to seedlings growing in soil) for both cryogenically and non-cryogenically stored embryonic axes (root–shoot axis). This protocol eliminates the need for conventional nut stratification; produces decontaminated tissue via surface sterilization, such that seedlings are visibly canker-free; increases germination; and enables long-term cryogenic storage.