A Commercialized Photoautotrophic Micropropagation System

Abstract

A photoautotrophic micropropagation system (called a PAM hereafter) that uses a sugar-free culture medium has many advantages over the conventional, photomixotrophic micropropagation system (hereafter referred to as PMM) that utilizes a sugar-containing culture medium [1]. The advantages include the use of large culture vessels with minimum risk of microbial contamination and the enhancement of plantlet growth at a high photosynthetic photon flux (PPF) and a high CO2 concentration inside the vessel [2,3] . In order to increase CO2 concentration in the vessel under pathogen-free conditions, both natural and forced ventilation methods have been employed. Putting gas-permeable filter disks on the vessel lid enhances natural ventilation [4]. Forced ventilation can be conducted by supplying CO2-enriched air with an air pump into the vessel through a gaspermeable filter disk [5]. The forced ventilation rate can be easily controlled during the production process by using an airflow controller, while the natural ventilation rate is difficult to change with passage of days [4]. In addition, it is difficult to obtain a high natural ventilation rate for a large vessel. Thus, for commercial production, forced ventilation is more convenient and practical than natural ventilation in a PAM that uses large vessels. Furthermore, many reports have shown that a PAM with forced ventilation considerably enhances the growth of plantlets compared with a PAM with natural ventilation. Fuziwara et al. [2] developed a 20-L vessel with forced ventilation for enhancing the photoautotrophic growth of strawberry (Fragaria x ananassa Duch.) plantlets during the rooting and acclimatization stages. Kubota and Kozai [6] used a 2.6L vessel containing a multi-cell tray with forced ventilation for photoautotrophic growth of potato (Solanum tuberosum L.) plantlets. Heo and Kozai [7] developed a similar system using a 12.8-L vessel for the photoautotrophic growth of sweet potato (Ipomoea batatas (L.) Lam.) plantlets. Heo et al. [8] developed another vessel of 11-L with air distribution pipes to improve an airflow pattern in the vessel for obtaining the uniform growth of sweet potato plantlets. Zobayed et al. [9] engineered a 3.5-L vessel with units of forced ventilation and sterile nutrient solution supply for uniform and enhanced growth of sweet-potato plantlets. Commercial application of the PAM may be