Effect of phenolic compounds on asparagus mycorrhiza

Abstract

Asparagus (Aspurugus o@iic~nulis L.) produces several cinnamic acid derivatives known to be allelochemicals (Young. 1984: Young and Chou. 1985; Hartung ef ul.. 1990). It has been suggested that these allelochemicals may either be directly involved in asparagus decline by affecting plant vigor (Young. 1984; Young and Chou, 198s) or indirectly through chemical-mediated changes in the microbial community (iiartung and Stephens. lYX3). which in turn aflcct plant growth. Wacker CI cl/. (199Ob) have shown that ferulic acid, an allclochcmical found in asparagus roots, decreases root colonization by vesicular arbuscular mycorrhirae (VAM) and the growth ol’ mycorrhiznl asparagus. Wackcr (*I ul. (IYYOc) I‘ound a change in the composition of the VAM fungal community in asparagus fields with increasing age up IO 20 yr. Root colonization by VAM fungi and spore density in the soil also c Wackcr cr ul.. IYYOa) plant health may be adversely alTected if the nutritional contribution to asparagus by native VAM fungal species decreases with plant age. Because available P decreased with increasing number of years cropped in asparagus, soil P may not be the factor responsible for the reduction in root colonization by VAM fungi and the change in the composition of the VAM fungal community observed by Wacker (1990~). Accumulation of phcnolic allclochcmicals produced by asparagus could be a mechanism by which asparagus monocropping alters the species composition of the VAM fungal community. WC report the etfrcts of’ fcrulic. catTcic and methylencdioxycinnamic (MDC) acids and also those of soil extracts from an asparagus field soil and an adjacent non-cultivated soil on VAM formation and growth of asparagus. To examine the etTccts of three phenolic acids on VAM formation in asparagus. asparagus seeds (cv. “Mary Washington”) were surface-sterilized (Elmer and Stephens, 1988). germinated and sown into plastic cell-pack units (2 x 2) with 8Og of washed sand per cell. A 9.0cm dia Petri dish base was used under each J-cell unit to avoid chemical cross-contamination. A VAM fungus resembling G/r~nlus/ct.vcicu/urunr (Thaxtcr) Gerd. and Trappc emend. Walker and Koske was multiplied in pot cultures with sorghum (.Sorlral seedlings. Alier transplanting, plants were watcrcd weekly with IO ml of 0.1 strength