Tamarindus indica L. leaf is a source of allelopathic substance Syeda Shahnaz Parvez 1,2, *, Mohammad Masud Parvez 2 , Eiji Nishihara 2 , Hiroshi Gemma 1 and Yoshiharu Fujii 2 1 Laboratory of Pomology, Institute of Agriculture and Forestry, University of Tsukuba, 1-1-1 Tennodai, Tsukuba Science City, Ibaraki, 305-8572, Japan; 2 Chemical Ecology Unit, National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba Science City, Ibaraki, 305-8604, Japan; *Author for correspondence (e-mail: ssparvez@yahoo.com; phone: +81-29-838-8246; fax: +81-29-838-8338) Received 28 August 2002; accepted in revised form 14 December 2002 Key words: Allelopathy, Growth Inhibition, Hypocotyl, Radicle, Sandwich Method, Tamarind Abstract The allelopathic potential of the Tamarindus indica L. leaf was investigated through bioassay guided studies using several weed and edible crop species. Both radicle and hypocotyl growth of all the plant species tested was strongly inhibited by the tamarind leaf using a sandwich method. The growth of weed species was reduced more than that of edible crop species. Among the weed species, barnyard grass followed by white clover, and in the edible crop species, lettuce followed by radish ranked top in terms of growth inhibition. Different concentrations of tamarind leaf crude water-soluble extract exhibited a strong inhibition in all the plant species tested and, by contrast, the magnitude of inhibition in the weed species was higher than in edible crop species and ranged from 30–75%. The 10% concentration of the tamarind leaf crude water-soluble extract was most potent against growth of seedlings. The concentrations of the nutrient components were linearly correlated with an increase in the con- centration of tamarind leaf crude water-soluble extract. No significant changes in either pH or EC were found in the variations of different concentrations of tamarind leaf crude water-soluble extracts. As compared to control, growth of both radicle and hypocotyl in weed (barnyard grass and white clover) and in edible crop (lettuce and radish) species were significantly reduced when blended tamarind leaves at different concentrations were incor- porated into the growth medium. The inhibitory magnitude increased with an increase in the concentration of the tamarind leaf. In terms of growth inhibition, among these tested plants, weed species particularly barnyard grass were most sensitive to the allelochemicals exuded from blended tamarind leaves. When the blended tamarind leaves were removed from the growth medium, all the seedlings grew quickly and the percentage of recovery was between 76–97% of the corresponding controls. Reduction in the fresh and dry weight of these 4 plant spe- cies was observed under the experimental conditions, and ranged between 33–42% and 40–53% in the radicle and hypocotyl, respectively. The fresh and dry weight, and total chlorophyll content declined significantly in the incorporated tamarind leaf treatments. Compared to the control, the highest drop in the chlorophyll content of 60% in barnyard grass was observed with the 10% concentration of the leaf treatment. These results clearly in- dicate that the tamarind leaf contains one or more strong biologically active allelochemical(s) that function as true growth regulator(s) and is involved in plant growth regulation, particularly in weed species. Introduction Allelopathy is a phenomenon by which allelopathic plants release chemical compounds into the environ- ment through root exudation, leaching by dew and rain, and volatilization or decaying plant tissues (Rice 1984). Allelopathy plays an important role in agro- ecosystems leading to a wide range of influences and interactions in biotic communities. Such influences and interactions are mainly a result of allelochemical release from the donor plants that generally have harmful effects on the receiver plants but a selective benefit to the donor. In recent years, improved ana- lytical methods have shown the allelopathy phenom- 107 Plant Growth Regulation 40: 107–115, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands.