Improved propagation efficiency in a laboratory–nursery interface for somatic embryogenesis in Norway spruce

Abstract

The aim of this work was to improve the protocol of somatic embryogenesis (SE) and propagation efficiency in Norway spruce (Picea abies (L.) Karst.), which would enable the integration of SE into Finnish breeding programme and the nursery practices applied to seedlings. The studies specifically investigated the following three areas: i) how maturation, cold storage, germination and growing conditions (laboratory-nursery interface) affect the survival and height growth of emblings (Papers I and II); ii) how to improve the efficiency of embling production from genotypes from wide genetic backgrounds (Papers I and II); and iii) how to increase propagation efficiency by rooting cuttings from emblings, and produce field testing material by combining SE and the rooting of cuttings (Papers II and III). To evaluate the possibility of improving the efficiency of SE in the laboratory-nursery interface, a series of experiments were conducted. The cost structure of SE, and the effects of improvements on costs, was estimated. As a result, the protocol improvements doubled the yield of cotyledonary embryos, nearly doubled embling survival, and increased the height growth of emblings in the nursery by so much that sufficient planting height was reached one year less than before. Emblings were also obtained from 356 genotypes (50% thawed), and embling cuttings rooted well in conditions similar to those used for seedling cuttings. The protocol improvements also reduced embling production costs by 75%. Based on this work, emblings may be grown in nurseries after one week of in vitro germination, without any measures that differ from seedlings after transplanting. Propagation efficiency may be further increased by rooting embling cuttings. Furthermore, large-scale clone testing can be initiated with 5-12 emblings acting as cutting donors.

How to Capture Thousands of Genotypes—Initiation of Somatic Embryogenesis in Norway Spruce

“…When the first forest regeneration material was compiled from a collection of families initiated in 2014, we were able to estimate an initiation threshold for 2019 families. The initiation threshold was achieved when the number of initiations that was estimated to produce enough cell lines was achieved from a family [7]. When this threshold was applied, the initiations were carried out in a short period (no excess cold storage), and cryopreservation was carried out in a larger number per cell line than was possible in 2014.…”

“…From the practical perspective, establishing field trials with SE plants requires numerous genotypes per family to ensure the possibility of genotype selection and to avoid reduced genetic gain [4][5][6][7]. To obtain the required number of plants for field testing, wellperforming cell lines should be initiated, i.e., lines that have vigorous proliferation, survive cryopreservation, and produce a large number of somatic embryos after cryopreservation [5,6].…”

“…Moreover, embryos must germinate and perform well in the nursery. For this, many initiations, 60 to 80 explants per family, from several families must be undertaken [7]. These preceding requirements regarding field testing combined with irregular flowering of Norway spruce in Finland lay out the framework for the magnitude of annual initiations for thousands rather than hundreds [8].…”

Interest in vegetatively propagated Norway spruce materials – a survey among Finnish forest owners and professionals

“…This is probably reflected also in the responses of the present study: Even if there is willingness to pay more, the acceptable price increment is relatively small, up to 24%, depending on the trait. The price of SE material has been previously evaluated to be at least twice that of seedlings due to high labour costs at certain steps of propagation requiring manual handling of individual embryos, and lower conversion rate compared to improved seeds (Lelu-Walter et al 2013), and the same cost structure is seen in Norway spruce SE (Tikkinen 2018). The acceptable price increment can thus be achieved only through automation of the labour-intensive part of the process, as already partly realised in Canada for white spruce and Norway spruce (Bonga et al 2019), and being developed elsewhere (Egertsdotter et al 2019) too.…”

Application of Cold Storage and Short In Vitro Germination for Somatic Embryos of Pinus radiata and P. sylvestris

“…The stages of germination and conversion of emblings into plants are extremely important to the overall success of SE on a commercial scale. Loss of plants during these latter stages greatly increases the overall cost of the technology, with the germination step being the most costly due to high labor demands [14][15][16]. Despite this, until recently, these stages of conifer SE protocols (germination and early plant growth) have been largely neglected in research efforts [8].…”