Growth, Opium Gum Yield, and Photoperiod Response of Five Opium Poppy Accessions

Flowering time, growth, and opium gum yield from five seed sources (T, L, B1, B2, B3) of opium poppy (Papaver somniferum L.) collected from different latitudes in three Southeast Asian countries were determined. Plants were grown in six growth chambers at a 11-, 12-, 13-, 14-, 15-, or 16-hour photoperiod with a 12-hour, 25/20 °C thermoperiod. Flower initiation was observed under a dissecting microscope (40×) to determine if time to floral initiation was identical for all accessions across a wide range of photoperiods. The main capsule was lanced for opium gum at 10, 13, and 16 days after flowering (DAF). Plants were harvested at 21 DAF for plant height, leaf area, and organ dry-weight determinations. In a 16-hour photoperiod, flower initiation was observed 10 days after emergence (DAE) for B1 vs. 8 DAE for the other four accessions. Flowering time was affected most by photoperiod in B1 and least in B2. Flowering times for B3, L, and T were similar across the range of photoperiods. B2, B3, and L had the highest gum yields per capsule; even though B1 had the greatest total plant biomass, it produced the lowest gum yield. There was no difference among accessions in the average ratio of gum : individual capsule volume. For the ratio of gum : capsule dry weight, only the difference between T and B1 was significant. Capsule size did affect these ratios slightly. T had a larger gum : volume ratio for larger capsules, and B3 had a smaller gum : dry-weight ratio for heavier capsules. Flowering time varied up to 40%, capsule dry weight up to 41%, and opium gum yield up to 71% for the five accessions across all treatments. No relationship was found between flowering time and the latitude where the seed sources were collected. Time to flower initiation could not be used to predict time to anthesis because floral development rates varied significantly among accessions and photoperiods. Capsule volume and dry weight were useful in estimating gum yield. Southeast Asian countries, especially Burma and Laos, are major producers of the opium poppy from which the narcotic drug heroin is manufactured. Production figures are used to make decisions about foreign aid and the allocation of resources to the War on Drugs. The U.S. Dept. of Agriculture (USDA) Agricultural Research Service (ARS) is developing methods for improving estimates of opium yields, an essential component for production estimates. A strong relationship between gum yield and capsule dry weight per unit land area was established during two field studies in Thailand (USDA–ARS, Systems Research Labotoperiod and 25 °C day/20 °C night temperatures, album DC flowers in 32 d. To accurately predict flowering time one must know how variable photoperiod response is among cultivars. The main objective of this study was to investigate variability in growth, flowering time, and opium gum yield among accessions grown at different latitudes in Southeast Asia. Specific questions to be answered were: Do accessions from various geographical locations respond differently to photoperiod? Can flowering time be predicted from time to flower initiation or from other more “observable” stages? Do accessions differ in opium gum yield? Is the opium gum yield from plants grown in controlled-environment chambers similar to that from field-grown plants? Does the ratio of opium gum yield : capsule volume or capsule dry weight differ among cultivars? Does this ratio depend on the size of individual capsules? Materials and Methods Seed source selection. Five seed sources (B1, B2, B3, L, and T) of opium poppy were selected from Burma, Laos, and Thailand (Table 1). These five sources represent common cultivars from the main growing regions in these countries, and were grown in widely varying latitudes. Plant culture and photoperiod treatments. Seeds were sown in 3.75-L pots filled with a Jiffy Mix growing medium (Jiffy Products, Batavia, Ill.) consisting of 1 Canadian sphagnum peat : 1 vermiculite (by volume). The growing medium was amended with a slowrelease fertilizer Osmocote (14.0N–6.1P– 11.6K) (Scotts-Sierra Horticultural Products Co., Marysville, Ohio) at a rate of 3 g·L. Dolomitic lime was added to adjust the pH of the medium to 6.5. The pots were placed in six reach-in controlled-environment chambers (Environmental Growth Chambers, Chagrin Falls, Ohio), with 30 pots in each chamber (six pots per accession). The six chambers were set at a photoperiod of either 11 (0800–1900 HR), 12 (0800–2000 HR), 13 (0800–2100 HR), 14 (0800–2200 HR), 15 (0800–2300 HR), or 16 (0800–2400 HR) h. Each chamber was provided with a combination of six high-pressure sodium and six metal halide lamps that were arranged alternately in three rows. Photosynthetic photon flux density inside the growth chambers was maintained at 1000 ± 100 μmol·m·s at the top of the plant canopy. Temperatures during the entire experimental period were controlled at 25 ± 1 °C during the ratory, 1992). To determine how variable this relationship might be, we examined plants from seed sources collected over a wide geographical range in Burma, Laos, and Thailand, and compared the results with data from the field studies. Since sampling for yields is necessarily limited and yet is a highly variable component of production, a simulation model that describes the effects of major environmental variables on yield is being formulated. Photoperiod is one of the most important variables that influence growth and flower development (Acock et al., 1996a; Gentner et al., 1975; Wang et al., 1997a, 1998) and thus can have a significant effect on opium yield. Opium poppy var. album DC is a long-day plant with a critical photoperiod near 16 h. In a 16-h phoTable 1. Seed source, accession code, plant identification number, and main flower characteristics of five opium poppy accessions. Accession ID Seed Flower Petal code no. source Latitude color edge B1 01179 Burma 20°40 ́ White Smooth B2 01286 Burma 22°53 ́ White Serrated B3 01425 Burma 24°04 ́ White Smooth L 01556 Laos 21°41 ́ Purple Smooth T 00064 Thailand 18°33 ́ White Serrated