PHYTOTOXICITY OF EXTRACTS FROM SORGHUM PLANT-COMPONENTS ON WHEAT SEEDLINGS

Wheat (Triticum aestivum L.) yield Is depressed when the crop is grown after gain sorghum [Sorghum bicolor (L.) Moench], a known allelopathic species. Since little is known about the variability of allelopathic potential among sorghum hybrids on wheat, six sorghum hybrids were selected from a 1989-1990 sorghum-wheat sequence for further study. The range in yield depression observed was 16%. The sis hybrids were grown in 1991 and separated into plant parts at maturity. A bioassay using wheat seedlings to detect allelopathic potential was developed. Bioassays of water extracts From mature seeds, glumes, leaves, sterns, and roots of sorghum were conducted to (i) quantify the allelopathic potential of sorghum on wheat; (ii) compare allelopathic potential of individual sorghum hybrids; and (iii) identify the plant parts that are the most important sources of allelopathic substances. Wheat radicle growth response to water extracts revealed a highly allelopathic hybrid and two hybrids with low allelopathic potential, These were retained for study in 1992. All plant parts, regardless of hybrid, contained water-soluble materials inhibitory to wheat seedling growth. Stems, iea fes, and toots were the most inhibitory components of a sorghum plant, reducing wheat radicle elongation by 74.7, 68.5, 64.0%, respectively, Within a sorghum hybrid, an individual giant part was not consistently allelopathic at the same level across years, Bioassays can rapidly detect the differences In allelopathic potential that may occur within and among hybrids. These results have implications for using sorghum-wheat rotations where residues of certain sorghum hybrids might negatively influence growth and development of wheat, possibly resulting in decreased wheat yields.