Biomass accumulation and alkaloid content in leaves of Erythroxylum coca and Erythroxylum novogranatense var. novogranatense grown in soil with varying pH

Abstract

Summary Erythroxylum coca var. coca Lam. ( E. coca ) and Erythroxylum novogranatense var. novogranatense (Morris) Hieron ( E. novo, novogranatense ) were grown in greenhouse pots of Monmouth sandy loam, over a pH range of 3.5 through 7.0, to determine patterns for biomass accumulation and the content of hygrine, tropinone, methyl ecgonine, cuscohygrine, tropacocaine, cocaine, cis - and trans -cinnamoylcocaine in their leaves. Optimal growth for E. coca occurred at pH 3.5, and for E. novo. novogranatense at pH 4.7 through 6.0. The pH extreme (sub-optimal biomass accumulation, above and below optimal pH) for E. coca was ≥6.5 and for E. novo, novogranatense ≤ 3.5 and ≥ 6.5. Hence, E. coca is tentatively termed a calcifuge (Al-tolerant, Fe-inefficient) while E. novo. novogranatense more nearly resembles a calcicole (Fe-efficient, Alsensitive). Increases in leaf alkaloid content observed at the pH extremes for E. coca and E. novo, novogranatense appeared to be caused by plant stress. E. novo. novogranatense was more tolerant to the high pH extreme than E. coca . Twenty-two months after transplanting, 55% of E. coca plants grown at soil pH 7.0 died, and those that remained were chlorotic. In addition, among E. coca plants grown at soil pH 6.5, only 55 % were alive at the third harvest. Cocaine concentration in E. coca was independent of leaf biomass. Leaves of E. coca grown in soil at pH 3.5 through 6.0 had higher concentrations of cocaine than those of E. novo. novogranatense . Conversely, leaves of E. novo. novogranatense contained a higher concentration of trans - and cis -cinnamoylcocaine and methyl ecgonine than those of E. coca . The least abundant alkaloid observed in E. coca and E. novo. novogranatense was tropinone which was low or commonly not detected. Of the eight alkaloids monitored in leaves of E. novo. novogranatense grown in soils at various pH levels, methyl ecgonine was the most abundant.