Collecting, Processing, and Treating Propagules for Seed and Vegetative Propagation in Nurseries

Abstract

Tropical plants can be regenerated either sexually (from seeds) or asexually (from vegetative portions of a donor plant). These sources are collectively called “propagules” and link the evolutionary processes of the past with the potential for future adaptation. Thus, the way propagules are collected, processed, and treated can have strong repercussions on the future health and diversity of tropical ecosystems. Matching propagule source with outplanting site and collecting a genetically and, when necessary, sexually diverse group of propagules ensure the future adaptability of the plants and success of reforestation and restoration projects.

Tropical seeds can be classified based on dormancy and potential for storage. Viviparous seeds germinate before dispersal from the mother plant. Recalcitrant seeds can germinate immediately once dispersed from the mother plant but lose viability when dried. Similarly, intermediate seeds can germinate immediately upon dispersal, but they also retain viability after some drying. Orthodox seeds can be dried without losing viability because they are “dormant.” A variety of methods exist to treat seeds to ensure germination. Methods for planting properly treated seeds include direct sowing of seeds, sowing germinants (sprouts), or transplanting emergents. Whichever technique yields the most efficient use of nursery resources depends on the species and the abundance and quality of the seeds.

Vegetative propagation uses stems, leaves, roots, or other portions of a single mother (donor) plant to produce genetically identical daughter plants and is commonly employed if seeds are unavailable or difficult to germinate or if some special characteristic of the donor plant needs to be exploited. Vegetative propagation is usually more labor intensive than seed propagation and therefore more expensive, especially if special propagation structures are required. The best portion of the mother plant to use, as well the best timing for collection and proper propagule treatment, varies by species and requires experience to discern. While some species readily grow from stem cuttings, others grow better from root cuttings, divisions, or layering. Grafting and micropropagation are options for rare and endangered species or others that are difficult to propagate by other methods.