Effects of Temperature and Light Levels on Leaf Yield and Cocaine Content in Two Erythroxylum Species

Published information on the response ofErythroxylum crops totemperature and photosynthetic photon flux density (PPFD) ismore descriptive than quantitative. The objective of this studywas to quantify the effects of temperature and PPFD on leafgrowth and cocaine content in the major cocaine-producing species.Plants ofErythroxylum coca var. coca (Coca) andErythroxylumnovogranatense var. novogranatense (Novo) were grown in artificially-lightedcontrolled environment chambers with a 12h photoperiod and atday/night temperatures of 20/16, 25/21, 30/26 or 35/31°Cand at PPFDs of 155, 250 or 400µmolm^-2s^-1for 53d beforeleaves were harvested for dry weight and cocaine concentrationdeterminations. Subsequently, chamber temperatures were alteredto provide constant day/night temperatures of 19, 23 or 27°C.Plants were grown for 180d under these conditions and harvesteda second time. Leaf yields in response to temperature were bestexpressed as quadratic functions. The optimum average dailytemperature for leaf growth was near 27°C in both species.Novo was more vegetatively vigorous than Coca. Leaf mass atthe first harvest was lowest in plants grown under 155µmolm^-2s^-1for both species. At the second harvest the only changewas that there was no difference in leaf mass between 155 and250µmol m^-2s^-1in Coca. Leaf cocaine concentration wasnot affected by PPFDs<400µmol m^-2s^-1but was affectedby temperature. In Coca, leaf cocaine concentration was maximumat a mean daily temperature of 24°C at the first harvestand at 19°C at the second harvest. In Novo, leaf cocaineconcentration was maximum at a mean daily temperature of 25°Cat the first harvest but there was no effect of temperatureat the second harvest. Coca leaves had higher cocaine concentrationthan Novo leaves at all temperatures at the first harvest butat the second harvest, there was no significant difference inleaf cocaine concentration between species except in the lowesttemperature treatment when leaf cocaine concentration was higherfor Coca. Cocaine production on a per plant basis was largelya function of leaf mass. Coca; cocaine; dry weight; Erythroxylum ; leaf yield; light; PPFD; species; temperature