Medicarpin delays alfalfa seed germination and seedling growth.
Dornbos D.L. Jr. | Spencer G.F. | Miller R.W.
The objective of this study was to identify a compound(s) that may be responsible, at least in part, for alfalfa autotoxicity. We found that medicarpin (3-hydroxy-9-methoxypterocarpan) is a compound produced by alfalfa (Medicago sativa L.) that contributes to this. A clay loam soil from a declining alfalfa stand with two plants per 930 cm2 and its 95% ethanol extract inhibited alfalfa emergence and seedling growth whereas extracted soil did not. The soil extracts contained at least 10 mg kg-1 medicarpin. Medicarpin, 4-methoxy-medicarpin, sativan, and 5'-methoxysativan were isolated from alfalfa foliage with 95% ethanol, purified, identified by gas chromatography-mass spectroscopy and then exogenously applied to alfalfa and velvetleaf (Abutilon theophrasti L.) seeds using an agar bioassay. Medicarpin at 1 X 10(-7) mole/seed reduced both alfalfa and velvetleaf seedling length by 39% after 72 h. Sativan and both methoxy derivatives had no effect on germination or seedling growth. In a timecourse study, 2 X 10(-7) mole/seed medicarpin delayed germination 12 h and seedling growth 44 h, during this time the alfalfa seedlings metabolized 85% of the medicarpin. Seedling growth then resumed at the control rate. Medicarpin is produced by mature alfalfa, is present in soil from a declining alfalfa stand, and is absorbed by alfalfa seedlings where it is metabolized and exerts a transient phytotoxic effect. Medicarpin may permit established alfalfa plants to control the ecology in their immediate proximity by inhibiting seedling establishment of nearby plants, thereby gaining a competitive advantage.
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