Optimizing axillary shoot culture as a short-term conservation method for American chestnut (Castanea dentata)

Abstract

Protocols were investigated in the short-term conservation of Castanea dentata (Marsh.) Borkh. to maximize axillary shoot multiplication rates at the genotype level and to reduce the incidence of shoot tip necrosis (STN). Factors investigated included explant growth stage (embryo, seedling, and mature stages) of the source material and two culture incubation temperatures (21 ± 1 °C and 31 ± 1 °C). Multiplication rate was measured across 22 genotypes. The role of 6-benzylaminopurine (0.5, 1.0, 2.0, and 4.0 μmol·L–1), calcium (3.0 and 6.0 mmol·L–1), boron (0.025 mmol·L–1), magnesium (3.0 mmol·L–1), and gelling agent (agar, 6.0, 7.0, and 8.0 g·L–1; gellan gum, 3.0, 3.5, and 4.0 g·L–1) on STN was investigated. Genotypes derived from 4-month-old seedlings had the greatest overall multiplication rate (7.87 ± 0.38 at 6 weeks). Temperature affected multiplication rate in three of eight genotypes tested, with multiplication rate greater at 21 ± 1 °C for one genotype and greater at 31 ± 1 °C for two genotypes. Multiplication rates differed significantly between genotypes and ranged from 1.45× at 12 weeks to 13.25× at 6 weeks. Incidence of STN was decreased to 1.40% ± 0.02% at 4.0 μmol·L–16-benzylaminopurine. The development of an efficient axillary shoot culture system for C. dentata greatly benefits current conservation efforts.