Effect of multiple subcultures on Musa shoots derived from cassava starch-gelled multiplication medium during micropropagation

Abstract

Shoot tip explants excised from in vitro plantlets of two Musa genotypes (TM3X 15108-6 and TMBX 612-74) were seeded singly into test tubes containing twenty milliliters each of Musa multiplication medium gelled differently in 60 and 70 gL-l cassava starch as well as 5 gL-l agar and placed on shelves under 14 h photo period (30-40 µmole m-2S-1) supplied by white fluorescent tubes. Temperatures were maintained at 27 ± 2oC. Monthly subcultures were carried out by separating shoot clusters developed from each explant into individual shoots and each shoot trimmed down and re-cultured as a shoot tip under the same conditions. This process was repeated for four months after which well formed shoots were subsequently transferred into a rooting medium. Cultured shoot tips grew and multiplied in the differently gelled medium. Shoots derived from starch-gelled medium after several subcultures became less robust than those grown on agar medium. This tendency for reduced robustness over time increased with increase in starch concentration in the medium and was more acute in TMBX 612-74 than TM3X 15108-6. Shoot water content after the fourth subculture revealed that shoots derived from agar-gelled medium had significantly (P=0.05) higher water content compared to shoots derived from starch gelled medium. This phenomenon must probably, is related to the availability of absorbable water in the differently gelled medium. Key words: Cassava starch, Musa shoot tips, micro-propagation, subculture