The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.
The milky liquid or latex derived from the unripe capsules of Papaver somniferum (or the opium poppy) has for many centuries been known to possess medicinal and mind altering properties. For example, ancient civilisations such as the ancient Egyptians used poppy latex in treatment for sleep inducement. The dried and powered form of latex is called opium. Opium comprises about five distinct chemical classes: phenanthrene, benzylisoquinoline, tetrahydroisoquinidine, cryptopine and miscellaneous. The alkaloid phenanthrenes, morphine, codeine and thebaine are therapeutic drugs. While thebaine is not medicinally useful in itself, it is usually converted into a useful derivative. Morphine and codeine are used principally for sedation and as analgesics. Given the low yields associated with synthetic approaches to these alkaloids, extraction from opium or poppy straw remains the major source of these compounds.
Several factors can adversely affect the alkaloid yield of and/or recovery from a given capsule obtained from poppy plant. Plant lodging, wherein the stem is displaced from its normal, essentially upright position, can result in poppy capsules lying close to or on the ground. As a consequence, the capsules may become weakened and alkaloid can leach out. Furthermore, significant lodging necessitates a different harvesting process which in itself may result in a decrease in the alkaloid recoverable from the capsule. Plant height can also affect alkaloid recovery. The straw obtained by harvesting poppy capsules contains a portion of stem as well as the capsule. Since the majority of the alkaloid is formed in the capsule, a large proportion of stem in the final straw reduces the amount of alkaloid recoverable from the straw. Similarly, if the ratio of seed weight to capsule weight is great, this could also decrease alkaloid yield or recovery.
Sulfonylurea compounds represent one of the largest classes of herbicides. These herbicides inhibit cell division and growth by inhibiting acetolactate synthase, a key enzyme in the first step of the biosynthesis of branched chain amino acids in bacteria, fingi and certain plants. Sulfonylureas are absorbed by plant foliage and roots to be transported to the tissues of the plant where cell division occurs. Cellular processes such as protein synthesis, nucleic acid synthesis, respiration and photosynthesis are not directly inhibited by these compounds, and thus the sulfonlyureas also provide excellent crop safety and low acute toxicity to humans and animals. Application rates of sulfonylureas for herbicidal purposes are typically in the g/ha level (compared to the kg/ha level for other typical herbicides), depending on the crop of interest. Typical ranges of use rates for a number of sulfonylurea herbicides, as applied to certain crops, are provided below (Russell, M. H. et al, Pesticide Outlook—August 2002, 166-173):
azimsulfuron(rice)5-25g/habensulfuron methyl(rice)20-70g/hachlorimuron ethyl(soybean, peanuts)8-13g/hachlorsulfuron(cereals, vegetable)9-25, 17-157g/haethametsulfuron(oilseed rape)15-23g/hamethylflupyrsulfuron methyl(cereals)8-10g/haiodosulfuron(wheat)7.5-10g/hamethyl sodiummesosulfuron methyl(wheat)10g/hametsulfuron methyl(cereals, rice, vegetable)3-7.5, 14-168g/hanicosulfuron(maize)35-70g/harimsulfuron(maize, potatoes,5-35g/hatomatoes)sulfometuron(vegetable)26-420g/hasulfometuron methyl(commercial/industrial150-600g/haareas, rights of way)sulfosulfuron(cereals)15-20g/hathifensulfuron methyl(cereals, maize,2-30g/hasoybeans)tribenuron methyl(cereals)9-18g/hatriasulfuron(sugar beet)18-35g/hatrifloxysulfuron(cotton)11-23g/hasodium
It has now unexpectedly been found that the application of certain sulfonylurea compounds to poppy plants, in amounts substantially less than those used for herbicidal activity, can alter one or more characteristics of the poppy plants, including reduction in plant height, reduction in lodging, reduction in seed weight and an increase in straw weight (through an increased weight proportion of capsule). One or more of these effects may advantageously provide improvements in harvesting of the poppy plants or, preferably, an increase in the alkaloid yield and/or recovery from the poppy plant.