Effects of temperature and light levels on leaf yield and cocaine content in two Erythroxylum species

Abstract

Published information on the response of Erythroxylum crops to temperature and photosynthetic photon flux density (PPFD) is more descriptive than quantitative. The objective of this study was to quantify the effects of temperature and PPFD on leaf growth and cocaine content in the major cocaine-producing species. Plants of Erythroxylum coca vat. coca (Coca) and Erythroxylum novogranatense var. novogranatense (Novo) were grown in artificially-lighted controlled environment chambers with a 12 h photoperiod and at day/night temperatures of 20/16, 25/21, 30/26 or 35/31 °C and at PPFDs of 155, 250 or 400 μmol m-2 s-1 for 53 d before leaves were harvested for dry weight and cocaine concentration determinations. Subsequently, chamber temperatures were altered to provide constant day/night temperatures of 19, 23 or 27 °C. Plants were grown for 180 d under these conditions and harvested a second time. Leaf yields in response to temperature were best expressed as quadratic functions. The optimum average daily temperature for leaf growth was near 27 °C in both species. Novo was more vegetatively vigorous than Coca. Leaf mass at the first harvest was lowest in plants grown under 155 μmol m-2 s-1 for both species. At the second harvest the only change was that there was no difference in leaf mass between 155 and 250 μmol m-2 s-1 in Coca. Leaf cocaine concentration was not affected by PPFDs ≤ 400 μmol m-2 s-1 but was affected by temperature. In Coca, leaf cocaine concentration was maximum at a mean daily temperature of 24 °C at the first harvest and at 19 °C at the second harvest. In Novo, leaf cocaine concentration was maximum at a mean daily temperature of 25 °C at the first harvest but there was no effect of temperature at the second harvest. Coca leaves had higher cocaine concentration than Nero leaves at all temperatures at the first harvest but at the second harvest, there was no significant difference in leaf cocaine concentration between species except in the lowest temperature treatment when leaf cocaine concentration was higher for Coca. Cocaine production on a per plant basis was largely a function of leaf mass.