A novel laboratory screening bioassay for crop seedling allelopathy.

Crops that control weeds by root exudation of allelochemicals are receiving increased attention, and there are efforts to breed allelopathic cultivars in several crops. The genetic improvement of allelopathic traits is based upon parental germ plasm with high allelopathic activity. Identification of allelopathic germplasm is done in laboratory screening bioassays, but experimental protocols are limited. We developed a fast and reliable laboratory screening bioassay for grain crops that includes dose-response considerations as an integral part of the experimental design. The bioassay was conducted in hydroponic culture, and a range of experiments with 2-(3H)-benzoxazolinone (BOA), an allelochemical of several grain crops, was carried out to define the basic protocol. Because of its sensitivity to BOA, Sinapis alba L. was selected as the receiver species. BOA affected growth (fresh weight and length of shoot and root), enzyme activities (ascorbate peroxidase, catalase, glutathione S-transferase, peroxidase, phenylalanine ammonia-lyase), and chlorophyll fluorescence, whereby root length was the most reliable response parameter. BOA sensitivity was dependent on nutrients for all parameters measured, and, thus, no nutrients were added. A set of experiments with Secale cereale L. and Triticum aestivum L. as donor species was carried out to optimize the protocol. Light and pH were eliminated as primary causes for the observed inhibition. The proposed bioassay has several methodological advantages over current bioassays.