Allelopathic effects of black pepper leachings on Vigna mungo (L.) Hepper

The possible physiological mechanisms behind the allelopathic effects of three concentrations of black pepper (Piper nigrum) whole plants leachings on germination, seedling growth, chlorophyll and chlorophyll supply-orientation (precursors for chlorophyll biosynthesis) in Vigna mungo var. NIAB were investigated. Fifty and 75% leaching solutions negatively affected germination and seedling growth of V. mungo. Maximum inhibition (58.11%) was recorded in germination at 75% leaching-treated seeds. In addition, seedling growth was also retarded by the application of leachings. Especially the affect on shoot growth was more evident with the increasing concentrations compared to root growth. In other experiment 10-day old etiolated seedlings of V. mungo were cultured in growth chamber in one-tenth Hoagland culture solution with or without leaching-concentrations. Leaves were harvested randomly at 0, 6, 12, 24 and 48-h time interval after treatment. The concentrations of chlorophyll, porphyrin and its three biosynthetic precursors such as proto porphyrin IX (Proto), Mg-proto porphyrin IX (Mg-Proto), and proto-chlorophyllide (Pchlide) were determined. Synthesis of chlorophyll and porphyrin was inhibited as the leaching concentrations increased. The mole percent of Mg-Proto affected by the leachings exhibited the same pattern as that of Pchlide and Proto. The data suggest that enzymes responsible for the conversion of porphyrin precursors may be the major targets of the leaching causing the significant decrease in chlorophyll concentration.