A comparative analysis of the development and quality of nursery plants derived from somatic embryogenesis and from seedlings for large-scale propagation of coffee (Coffea arabica L.)

Plants of Coffea arabica L. derived via somatic embryogenesis, namely, somaclones, were evaluated with C. arabica seedlings grown in the nursery. At the time of their transfer to the nursery, somaclones of C. arabica cvs. Caturra and Costa Rica 95 (Catimor) were smaller and less vigorous than seedlings of the same cultivars. Following an initial slow growth for a period of 10 weeks, somaclones began to grow faster than seedlings until both groups of plants were equal in size at 21 weeks (entire duration of growth in the nursery). Comparisons of aerial and root systems of 30-cm long somaclones and seedlings of two cultivars revealed that plants of somaclones were more vigorous than seedlings, based on the higher number of leaves (13-16 vs. 9), larger leaf area (1060-1280 vs. 730-890 cm(2)), and greater dry weight of aerial organs (8.5-12 vs. 7.0-7.5 g). For cv. Caturra, the root dry weight of somaclones was significantly greater than that of seedlings (2.7 vs. 1.9 g) and was attributable to the large diameter roots (> 0.5 mm). Analysis of 176,000 F-1 hybrid somaclones revealed that these exhibited more heterogeneous growth than did the seedlings derived from zygotic embryos; moreover, there was a genotype effect. Almost 9-20% of somaclones required an additional 3-4 months of growth in the nursery, and 8-12% were culled for other undesirable horticultural attributes. Only 0.10-0.23% of somaclones displayed variant phenotypes. The observed somaclone vigor in the nursery was carried over to field performance as these plants were more precocious than seedlings and yielded coffee beans 1 year earlier than seedlings.