How timing of sampling can affect the outcome of the quantitative assessment of plant organogenesis

• Plant growth can be described by a sigmoidal growth curve.
• Hybrid Cymbidium PLB development was assessed at 7 time intervals.
• Apple shoot development was assessed at 5 time intervals.
• Ideal sampling time depended on the intended use of plant material in Cymbidium.
• Timing of sampling should fit the genotype and physiological state of the explant in apple organogenesis.

Growth in plant cell or organ size, mass or number over time can be described mathematically by a sigmoidal growth curve with different phases characterized by different growth rates. Therefore, the timing of sampling strongly influences the quantitative outcome of a study and is of great importance if the efficacy of a protocol is to be evaluated. The use of different explants can also influence the timing (or speed) of the developmental outcome, but the impact is not as great as the timing of sampling. In this study, two plant species (an orchid and apple) were used to demonstrate the role of sampling time for evaluating tissue culture experiments, and its impact on the conclusions drawn there from. Using protocorm-like bodies (PLBs) of hybrid Cymbidium Twilight Moon ‘Day Light’ (Orchidaceae), the development of newly formed PLBs was assessed and quantified at seven time intervals: 10, 20, 30, 45, 60, 90 and 120 days. The optimal timing lay between 45 and 60 days, just prior to the PLB forming a shoot. In addition, using two apple (Malus × domestica) scions with different regeneration abilities (easy-to-regenerate ‘Royal Gala’ and difficult-to-regenerate ‘Freedom’), the development of adventitious shoots on leaf segments was assessed after 5 culture intervals: 28, 35, 42, 49 and 63 days. The effect of genotype and the position of the source leaf on the quantitative outcome of adventitious shoot regeneration on leaf explants are presented. With such wide margins of interpretation for both species, caution should be taken by researchers who extrapolate beyond what is reported in a paper for one genus, species or cultivar for application to other germplasm, even if within the same phylum.