Witchweed seed germination stimulant

The compound (I) was given the trivial name strigol and it has been shown to be a very potent witchweed seed germination stimulant. 

Eplee, R.E. 1975. Ethylene a witchweed seed germination stimulant. Weed Sci. 23, 433-436... 

Formation of the 3j8-acetoxyeti-5-enic esters has been used to obtain optically pure samples of (+)- and (—)-tran5-verbenoP and to resolve an alcohol intermediate in the synthesis of the witchweed seed germination stimulant (+)-strigol. A general synthesis of thiol esters from carboxylic acids, exemplified by the formation of the n-propylthio-, isopropylthio-, and t-butylthio-esters of cholic acid, comprises reaction with diethyl chlorophosphate-triethylamine, followed by the thallium(i) salt of the appropriate thiol. 

The germination stimulant or stimulants from host plants have not yet been identified, but research on isolation and identification of these allelopathic compounds continues. Other nonhost plants, such as cotton, also release chemicals which stimulate the germination of witchweed seed and these crops can replace the cereal crops in witchweed-infected fields. If no acceptable host is present, the witchweed plant is unable to mature and produce seed. The importance of cereal crops as a staple food in underdeveloped countries makes growth of nonhost crops only partially acceptable, and there are numerous wild hosts that allow the witchweed to germinate, mature, and produce more seed (several thousand seeds can be produced by a single plant). Nevertheless, application of either natural or synthetic stimulants in the absence of a host plant is an effective way of reducing and eventually eliminating the witchweed problem. 

Hsiao, A. I., Warshem, A. D., and Moreland, D. E. 1988. Effect of chemicals often regarded as germination stimulants on seed conditioning and germination of witchweed (Striga asiatica). Ann. Bot. 62, 17-24... 

Witchweed seeds must be kept in a moist environment at 20 to 30°C for 1-3 weeks before the stimulants can initiate germination (4,15,39,40). This process is defined... 

Table I. Germination of Witchweed Seeds Conditioned in Water at 30°C for 7 and 14 Days Followed by 24-h Terminal Treatment with Brassino-lide, d/-Strigol, and Natural Stimulants at 30°C in the Dark ...

Figure 1. Germination of Witchweed Seeds Conditioned in Water and Brassinolide (10 7M) for 3-7 Days before Terminal Treatment with Natural Stimulants. Bars Represent Standard Errors of Means for 3 Replications over 3 Experiments.

Table V. Germination of Witchweed Seeds Conditioned in Various Plant Growth Regulators at 30°C for 7 Days with and without Terminal Treatments of Natural Stimulants (4-fold Diluted) from Sorghum at 30°C Conditioning media Germination (%)...

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