Sustained Caulogenesis in Callus Cultures of Larix × Eurolepis Initiated from Short Shoot Buds of a 12-Year-Old Tree

Abstract

Caulogenic callus cultures were established from vegetative short shoot buds collected from cuttings from a ca. 12-year-old tree of Larix × eurolepis. Schenk and Hildebrandt basal medium supplemented with various concentrations of 6-benzylaminopurine (BAP, 2.5 × 10–7 to 1.0 × 10–5 M) or BAP (5.0 × 10–6 M) + indolebutyric acid (IBA, 1.0 × 10–6 M) was used. Subcultures were carried out on the same medium as used for initiation. Shoot formation resulted mostly from adventitious organogenesis on callus tissue, but adventitious organogenesis and axillary shoot development were occasionally observed on neoformed shoots. Series initiated in December 1984, June 1985, and August 1985 were still very productive after 32, 26, and 24 months respectively in culture. Sampling date of the primary explants had a pronounced effect on i) initial survival rate, ii) number of subcultures before establishment of continuous, vigorous cultures, and iii) number of subcultures before attaining a high percentage of caulogenic calli and good productivity. Browning of callus tissue with time during each subculture was concomitant with an increase in shoot productivity. Most neoformed shoots did not show pronounced elongation of the stem in vitro. Some shoots entered dormancy, and either stayed dormant upon subculture or resumed growth. Depending on the concentration of growth regulators used during callus culture, between 4 and 22% of excised shoots rooted when transferred first on DCR medium without growth regulator (Gupta and Durzan, 1985) and then twice on DCR-1 medium (Gupta and Durzan, 1985). Rooted shoots elongated after a few weeks in greenhouse conditions.