Pak. J. Bot., 42(5): 3587-3604, 2010. ALLELOPATHIC EFFECTS OF CENCHRUS CILIARIS L. AND BOTHRIOCHLOA PERTUSA (L.) A. CAMUS FARRUKH HUSSAIN 1 , BASHIR AHMAD 2 AND IHSAN ILAHI Department of Botany, University of Peshawar, Pakistan 1 Centre of Plant Biodiversity, University of Peshawar, Pakistan 2 Centre of Biotechnology and Microbiology, University of Peshawar, Pakistan Abstract Cenchrus ciliaris L., and Bothriochloa pertusa (L) A. Camus are perennial range grasses growing from plains upto 1000m in hot and dry tropical and subtropical regions of the world including Pakistan. Both these grasses are preferred for pasture due to easy germination, fast growth, good palatability and better productivity. However, the pasture generally declines after few years. The present study was conducted to see if allelopathy might be responsible for the declination of pastures. Studies made with using aqueous extracts and added mulches from different plant parts indicated that extracts from various parts and mulches invariably inhibited the germination, radicle growth, dry weight and moisture contents of test species used in different bioassays and experiments. The toxicity depended upon the parts assayed, test species used, soaking duration and physiological parameter. Above ground parts, especially leaves, were more toxic than roots. The toxicity enhanced with increasing soaking duration and amount of plant material. However, the toxicity of shoots declined with constant leaching of plant material. Shoot mulches added to soil retarded the germination and dry weight of test species. It was observed that allelopathy operates through water soluble toxins. However, further study is needed to see the role of root exudates, rains leachates and to identify phytotoxins. Introduction Cenchrus ciliaris L., and Bothriochloa pertusa (L.) A. Camus are perennial range grasses growing from plains upto 1000m in tropical and subtropical region of the world including Pakistan. These grasses are preferred for their prompt germination and establishment of seedlings, better forage production and good palatability and their ability to with stand grazing and drought pressure. It has been observed that pure pastures of these grasses need reseeding after 4-5 years even under favourable conditions (Brown, 1966). Vyas (1965) reported that these grasses dominate in grassland communities that change to Cenchrus or Bothriochloa type of grassland under grazing. Bishop et al., (1974) attributed the decline of Cenchrus pasture to competition. Akhtar et al., (1978) in a preliminary study hinted upon the possibility of allelopathy by these grasses. Hussain et al., (1982) stated that competition alone can not be responsible for the reported decline of growth of Cenchrus ciliaris and Bothriochloa pertusa. They further pointed out the possibility of allelopathy by these grasses in mixed cultures. Allelopathy operates in nature in many species including grasses through water soluble toxins that reach to the immediate habitat by various mechanisms (Hoque et al., 2003; Kadioglu & Yanar, 2004; Hussain et al., 2004, 2005; Nusr & Shariati, 2005; Ko et al., 2005; Iman et al., 2006; Batlang & Shushu, 2007; lannucci, 2007; Thapaliyal et al., 2007; Samreen et al., 2009; Hisashhi et al., 2009). Allelopathy is a complex process that operates along with competition in nature to suppress and finally exclude the susceptible associated species from the common habitat. It has been frequently observed that allelopathically