Allelopathic potential of mexican sunflower [tithonia diversifolia (hemsl) a. Gray] on germination and growth of cowpea seedlings (vigna sinensis l.)

Abstract

Allelopathy is a common among plants. Allelopathic substances affect seed germination, plant growth and development or even affect chlorophyll synthesis by the plant leaves. Tithonia diversifolia contains allelochemicals that inhibit growth of many agricultural crops. A study was conducted at Maseno University (Kenya) to investigate the allelopathic effects of T. diversifolia on the germination of seeds, growth and synthesis of chlorophyll of seedlings of cowpea (Vigna sinensis). Cowpeas seeds and seedlings were subjected to four different concentrations of the fresh shoot aqueous extracts which comprised of 0 (tap water), 25%, 50%, 75%, and 100%. Twenty Seeds of cowpeas were germinated in sterilized petri dishes lined with a layer of filter paper whatman no. 1, moistened with 10ml of each extract concentration and tap water respectively. Germination percentage, plumule and coleoptiles length were determined at the end of the study. Individual cowpeas seedlings were planted in 4.5 litres plastic pots containing soil and irrigated with the various shoot extracts concentrations and tap water using 500ml respectively. The treatments were replicated five times and the pots laid out as completely randomized design in the glasshouse. Data on shoot height; number of leaves per plant was recorded on weekly basis. Leaf area, shoot and root dry weights and leaf total chlorophyll, chlorophyll a and b concentration were determined at the end of the experiment. Data collected was subjected to analysis of variance (ANOVA) using SAS statistical package. Treatment means were compared using the least significant difference (LSD) at (P<0.05). The results revealed that fresh shoot aqueous extracts of T. diversifolia have both inhibitory and stimulatory effects on V. sinensis. Seed germination increased with increasing concentration of shoot extracts from 25%, 50% to 100% even though there were no significance differences among treatments. Plumule and radicle lengths reduced significantly among treatments. Shoot heights, leaf number, leaf area, shoot and root dry weights, total chlorophyll and chlorophyll a and b concentrations increased significantly with increasing shoot extract except at 100% treatment where all these parameters were inhibited.