Gum Yield as Affected by Capsule Age, Firmness, Gum Collecting Methods, and Phenotypes in Opium Poppy

Abstract

The U.S. State Dept. annually publishes estimates of narcotic drug crop production worldwide. The areas under cultivation are well known but yields per unit land area are not. Determining opium gum yield from illicitly grown poppy Papaver somniferum L. is difficult and dangerous. Removing plants from the field and harvesting gum in a safe place would allow us to measure gum yield from one short field visit. To interpret these results in terms of total gum yield from the field, one must know how the measured gum is affected by gum collecting method, capsule age, and phenotype. Opium poppy seeds from three phenotypes (purple, white, and red-white flowers) were grown in a greenhouse and plants were either cut at the soil level or left intact for opium gum harvest at 7, 12, and 22 days after flowering (DAF). Capsule firmness was measured to estimate gum yield and capsule age, and the relationship between total gum yield and yield from the first lancing was examined. The average gum yield (8.4 mg·g–1 dry weight capsule) for the purple-flowered phenotypes was 17% and 25% lower than for the white- and red/white-flowered phenotypes, respectively. Capsule firmness of the three phenotypes varied from ≈800 to 2300 N·m–1 as the capsule aged. Gum yield and capsule firmness increased with capsule age but the timing of those changes differed among phenotypes. No significant correlations were found between capsule firmness and gum yield or between capsule firmness and age. Therefore, capsule firmness cannot be used to predict gum yield or capsule age. Gum yield from the first lancing was linearly correlated with total gum yield (r2 = 0.82). Since this relationship changes with growing condition, it is insufficient to predict total gum yield. Gum yield from cut plants was significantly lower than from intact plants for all three phenotypes at 22 DAF and for white-flowered phenotypes at 12 DAF. No difference in gum yield was observed between cut and intact plants at 7 or 12 DAF for purple and red/white-flowered phenotypes. The relationship between gum yield from cut and intact plants was too variable to predict gum yield from intact plants by measuring gum yield from cut plants.