Screening of high biomass and phenolic producing clonal lines of Spearmint in tissue culture using Pseudomonas and azetidine-2 carboxylate.

Rosmarinic acid (RA) and related phenolics are natural antioxidants found as secondary metabolites in spearmint (Mentha spicata). These phenolic-secondary metabolites have diverse food processing and nutraceutical applications. Since natural cross-pollination results in plant to plant variation in the level of phenolic metabolites, tissue culture-based techniques are essential to isolate elite antioxidant-producing clonal lines. The objective of this research is to develop tissue culture-based selection techniques to isolate high rosmarinic acid and phenolic-producing clonal lines from a heterogenous bulk seed population of spearmint. Multiplied clonal shoots of each line were screened for tolerance to azetidine-2-carboxylate (A2C). Individual shoot apex of each line were also screened for Pseudomonas tolerance. Rosmarinic acid and total phenolics were assayed in all treated clonal lines and compared to uninoculated/untreated shoot explants of corresponding line. The Pseudomonas and A2C treatment strategy allowed the rapid tissue culture-based screening of potentially high phenolic antioxidant-producing clonal lines of spearmint for future field and greenhouse evaluation. Targeted elite lines had combinations of Pseudomonas tolerance with no loss in biomass in response to the bacterium and enhanced levels of total phenolics and rosmarinic acid in response to A2C.