Biological contaminants associated with in vitro establishment of nursery-derived sweetpotato shoots

Abstract

The production of virus-free sweetpotato planting material is essential for sustainable seed systems and commercial crop production. However, microbial contamination during in vitro establishment remains a major limitation to successful tissue culture propagation. This study aimed to identify the major biological contaminants associated with nursery-derived sweetpotato shoots during in vitro establishment and to determine whether the age of the shoot influences contamination levels.
Nodal shoots of the cultivar Minj Purple were collected from nursery-grown plants at 2, 6 and 12 weeks of regrowth. Explants were surface sterilised using a sodium hypochlorite-based protocol and cultured under standard in vitro conditions. Contaminated cultures were classified into broad microbial groups based on visible morphological characteristics.
Fungi, yeast and bacteria were identified as primary biological contaminants during culture establishment. The overall contamination frequency was 65.8%, with fungal contamination occurring most frequently (48.8%), followed by yeast (15.4%) and bacteria (1.6%).  The age of shoots had no significant effect on contamination levels during in vitro establishment, whereas contaminant type significantly influenced contamination frequency, with fungi being the predominant contaminant.
These results provide baseline information on biological contaminants affecting sweetpotato establishment at Aiyura. Improved nursery sanitation, targeted fungal management and refined sterilization protocols are necessary to reduce contamination losses in resource-limited tissue culture systems.