In vitro propagation of Plant Genetic Resources is a basic step for routine genebank and biotechnology research activities. Accelerating growth and rooting of in vitro plants contributes to an improvement in process efficiency and plant quality. In the present study the effect of supplemental thiamine and explant size on biometric variables, ion content in plant sap, chlorophyll content in leaves and moisture content in plants were assessed in a replicated trial on a group of seven in vitro sweetpotato accessions and validated in a set of other 45 accessions. It was shown that adding 0.1 mg L −1 of thiamine to modified Murashige and Skoog culture medium significantly increased plant height, root length, and number of nodes of in vitro sweetpotato shoot culture plants. No significant differences were observed for N03−, K+, Na+ and Ca++—ion content in plant sap, nor in leaf area, chlorophyll, or moisture content between plants grown with or without thiamine. Uninodal stem segments showed on thiamine-free medium a significantly lower root and plant growth, and reduced number of nodes, than plants grown from uni- and binodal segments on thiamine-supplemented medium. A subsequent experiment tested all the parameters above in a non-replicated screen with a set of 45 diverse sweetpotato accessions. With this diverse set of germplasm, the average plant and root length increased by 41 and 51%, respectively on thiamine-supplemented culture medium compared to the control treatment, confirming that supplemental thiamine is generally beneficial to sweetpotato in vitro shoot culture.

Fast and reliable propagation of plant material is an important need in different stages of breeding programs and production systems. In vitro propagation ensures that pathogen- and virus-free plants stay phytosanitary clean over time while providing high multiplication rates. Using liquid instead of solid culture medium can reduce the interval of individual propagation cycles and contributes to speeding up of the process (1.5–2.5 times), especially during the initial growth phase of the plants. Sophisticated immersion systems have been developed for many plant species, but they are difficult to apply when hundreds or thousands of different genotypes are propagated simultaneously. Additionally, these systems require a high input of technical equipment, know-how and experience to avoid bacterial or fungal contamination during the propagation process. The following protocol describes a low-input suspension technique that combines the use of liquid and solid medium, and permits the successful propagation of genetically diverse sweetpotato genotypes [Ipomoea batatas (L.) Lam.] with a high multiplication rate. As sweetpotato is an important staple crop in low-income/technology countries of Africa, Asia, and South America, the described method may find valuable application for the breeding programs in these regions.