EFFECTS OF TEMPERATURE AND LIGHT LEVELS ON LEAF YIELD AND COCAINE CONTENT IN 2 ERYTHROXYLUM SPECIES

Published information on the response of Erythroxylum crops to tempera ture and photosynthetic photon Bur density (PPFD) is more descriptive than quantitative. The objective of this study was to quantify the eff ects of temperature and PPFD on leaf growth and cocaine content in the major cocaine-producing species. Plants of Erythroxylum coca var. coc a (Coca) and Erythroxylum novogranatense var. novogranatense (Novo) we re grown in artificially-lighted controlled environment chambers with a 12 h photoperiod and at day/night temperatures of 20/16, 25/21, 30/2 6 or 35/31 degrees C and at PPFDs of 155, 250 or 400 mu mol m(-2) s(-1 ) for 53 d before leaves were harvested for dry weight and cocaine con centration determinations. Subsequently, chamber temperatures were alt ered to provide constant day/night temperatures of 19, 23 or 27 degree s C. Plants were grown for 180 d under these conditions and harvested a second time. Leaf yields in response to temperature were best expres sed as quadratic functions. The optimum average daily temperature for leaf growth was near 27 degrees C in both species. Novo was more veget atively vigorous than Coca. Leaf mass at the first harvest was lowest in plants grown under 155 mu mol m(-2) s(-1) for both species. At the second harvest the only change was that there was no difference in lea f mass between 155 and 250 mu mol m(-2) s(-1) in Coca. Leaf cocaine co ncentration was not affected by PPFDs less than or equal to 400 mu mol m(-2) s(-1) but was affected by temperature. In Coca, leaf cocaine co ncentration was maximum at a mean daily temperature of 24 degrees C at the first harvest and at 19 degrees C at the second harvest. In Novo, leaf cocaine concentration was maximum at a mean daily temperature of 25 degrees C al the first harvest but there was no effect of temperat ure at the second harvest. Coca leaves had higher cocaine concentratio n than Novo leaves at all temperatures at the first harvest but at the second harvest, there was no significant difference in leaf cocaine c oncentration between species except in the lowest temperature treatmen t when leaf cocaine concentration was higher for Coca. Cocaine product ion on a per plant basis was largely a function of leaf mass. (C) 1996 Annals of Botany Company