Allelopathic effects of rhazya stricta on seed germination of some range plant species

Abstract

Rhazya stricta Decne., an evergreen poisonous shrub, has invaded large areas ofovergrazed rangelands in Saudi Arabia. To understand the mechanism by which this noxiousplant spreads, a laboratory experiment was conducted to assess its allelopathic potential to thegermination of some range plants. Leachates were prepared from fresh and dry foliage of .Rstricta.Seeds were germinated in petri dishes moistened with either leachates or tap water .Leachates inhibited germination with fresh foliage leachate being most severe. Completegermination inhibition was observed in Farsetia aegyptia and Pennisetum divisum. Haloxylonsalicornicum and Lasiurus scindicus were the least affected. Rate of germination was also.significantly reduced H. salicornicum was the least affected (56 and 25% in presence of dryand fresh leachates respectively), while other species were drastically reduced. Washing andregermination of the remaining non-germinated seeds indicated that seed viability of .Faegyptia and P. divisum may have been lost in presence of leachates. Osmotic effects ofleachates may have contributed to germination inhibition in Atriplex halimus, Achilleafragrantissima, L. scindicus and R. strictaWhile inhibiting early germination of other .,species R. stricta needs enough water to leach water soluble inhibitor present in its seeds.which in turn would also be sufficient to overcome osmotic effect of foliage leachate.