Allelopathic sorghum aqueous root extracts inhibit germination and seedling growth of crops and weeds

Allelopathic sorghum aqueous extracts can be used as sprays against weeds of arable lands. Water-soluble allelochemicals in the aqueous extracts may also negatively affect crops. Root aqueous extracts from the South African landrace sorghum IS9456 and the Botswanan commercial variety Mahube, with high (584.69 µg mg-1 root fresh weight) and low (17.38 µg mg-1 root fresh weight) sorgoleone contents respectively, were tested on germination, radicle length, plumule length and dry weight of goosegrass [Eleusine indica (L.) Gaertn], blackjack [Bidens pilosa (L.)], maize [Zea mays (L.)], soya bean [Glycine max (L.) Merr.] and wheat [Triticum aestivum (L.)]. Factors in five glasshouse experiments were the two sorghum varieties and four root extract solutions (0%, 5%, 10% and 20%) (w/v) arranged in a randomised complete block design with six replications. There was no significant effect (P>0.05) of variety and root aqueous extract on germination, radicle length, plumule length and dry weight of maize and on germination of wheat and goosegrass. The sorghum accession IS9456 significantly (P<0.05) reduced plumule length and dry weight of wheat and goosegrass and germination, plumule length and dry weight of soya bean and blackjack compared to Mahube. Increasing strength of root aqueous extract solution significantly (P<0.001) reduced plumule length and dry weight of wheat and goosegrass as well as germination and dry weight of soya bean and blackjack. Extracts from IS9456 had greater inhibitory effects on crop and weed germination and growth compared to those from Mahube. Due to its low sorgoleone content and weak weed suppression from its root aqueous extracts, Mahube may have low potential for use in allelopathic weed control. The sorghum accession IS9456, which also produces very high sorgoleone content, may be used in integrated weed management exploiting allelopathy from both sorgoleone and water-soluble allelochemicals, although farmers will have to be careful in terms of crop rotations since the aqueous extracts also inhibit germination and growth of some crops. Field studies may be required to further confirm allelopathic effects of root aqueous extracts from IS9456.