Somatic embryogenesis-derived coffee plantlets can be efficiently propagated by horticultural rooted mini-cuttings: A boost for somatic embryogenesis

In general, the current industrial somatic embryogenesis (SE) propagation processes for coffee are costly because they are not productive enough. We show that SE-derived plantlets from C. arabica hybrids were temporarily − between 10 and 25 weeks of development in nursery − able to root with a high success rate (up to 90%) whatever the genotype tested, before gradually losing that capacity. We took advantage of this transient rooting capacity, probably due to the rejuvenation process occurring during SE, to establish a new propagation system based on the continuous culture of rejuvenated SE plants and on the serial rooting of cuttings under nursery conditions, known as horticultural rooted mini-cutting (HRMC). The excessively low SE efficiency with an embryo-to-plantlet conversion rate of only 37% can be greatly offset by the much higher HRMC multiplication rate (14 in six months) and better overall quality. Fifteen week-old rooted mini-cuttings proved to be more uniform (2-4.5 vs.1-5.5 cm for plant height distribution) and vigorous (1.41 vs. 0.81 mm for stem diameter) than same-age somatic seedlings. This effect persisted for five years after field planting, mainly through a slightly greater collar diameter (43.3 vs 40.6 mm), whereas at root level no differences were found. The HRMC method is expected to dramatically reduce arabica hybrid production costs (by up to 50% at US$ 0.27/plant ready for field planting) and thus to promote the mass utilization of genetically superior hybrid clones of coffee.