Improvement of scaled-up somatic seedling production in hybrid sweetgum (Liquidambar styraciflua×L. formosana)
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Some clones of hybrid sweetgum (Liquidambar styraciflua×L.formosana,), the hybrid of American sweetgum (Liquidambar styraciflua) and Chinese sweetgum (L. formosana), demonstrate increased vigor, accumulating biomass faster than elite native sweetgum. Somatic embryogenesis is a primary method to micropropagate hybrid sweetgum. Considerable progress in developing somatic embryogenesis as a mass clonal propagation system for hybrid sweetgum has been made in recent years, but labor costs remain the largest cost component of the system. Different bioreactors had been considered for their potential to improve the efficiency of the system and thus decrease labor costs by decreasing the total process time. Air-lift bioreactors have been successfully applied to improve growth efficiency in some woody species. Stirred-tank bioreactors can be helpful for optimizing proliferation protocol because culture conditions can be controlled. Using two genotypes of hybrid sweetgum (28-1-5A, 28-1-8), we tested proliferation of suspension cultures of PEMs in airlift bioreactors and stirred-tank bioreactors, compared to culture in shaken flasks. Airlift bioreactors showed 12.6% and 104.2% faster growth rates in two genotypes compared to flasks. Thus, the use of airlift bioreactors has the potential to lower costs during the proliferation stage of this propagation system. Stirred-tank bioreactors were used to monitor the consumption of different sugars (sucrose, glucose and fructose) by the growing tissue, with differential use of different sugars being found during proliferation. Bioreactors with temporary immersion designs, such as the RITA®, have been applied to improve in vitro propagation of a number of woody species. We tested RITA®s for their potential to improve the production efficiency of high-quality hybrid sweetgum somatic seedlings in comparison to somatic seedlings from embryos germinated on semisolid medium in GA7 vessels. In hybrid sweetgum genotype 28-1-5A, RITA® units with 50 embryos had about 20% higher high-quality somatic seedling production frequency (p<0.05) and about 35% higher conversion frequency (p<0.05) than the GA7 vessels. In all genotypes we tested, somatic seedlings germinated in RITA® bioreactors had statistically higher survival frequencies than somatic seedlings germinated in the GA7 vessels.