Allelopathic Effects ofEucalyptus Saligna on Germination Growth and Development of Vigna Unguiculata L.Walp

Abstract

Allelopathic effects of Eucalyptus are widely reported and considered the major factor limiting the establishment of native species in eucalyptus forest. Allelopathy is used here to refer to the inhibitory and stimulatory effects of one plant species upon another by the compounds arising from the products of their metabolism. Improved germplasm of Eucalyptus developed through traditional breeding, tissue culture technique and other biotechnology researches are becoming an attractive alternative to other hardwood tree species for wood, pulp and paper, and bioenergy applications in many countries. In Eucalyptus plantations established for research and commercial end use, allelopathy has been raised as a concern for possible negative effects on crops grown in local areas, especially in agroforestry systems. In this study Eucalyptus saligna is used. E. saligna is thought to possess phenolic acids released from the leaves, bark and roots that have deleterious effects on other plant species. Cowpea (Vigna unguiculata L.Walp), an annual legume which originated in Africa is widely grown for grain crop, animal fodder and as a vegetable. The main objective of the study was to determine the allelopathic effects of Eucalyptus saligna on the germination, growth and development of Vigna unguiculata L. Walp. The study was conducted at Maseno University, Kenya, to investigate specifically the allelopathic effects of E. saligna on the percentage germination of seeds, rate of germination, growth of different parts of the plant species and synthesis of chlorophyll of seedlings of cowpea (Vigna unguiculata). Cowpeas seeds were subjected to four different concentrations of the fresh shoot aqueous extracts which comprised of 0% (distilled water), 25%, 50%, 75%, and 100%. Ten seeds of cowpeas were germinated in sterilized petri dishes lined with a layer of filter paper Whatman no. 1, moistened with 10ml of each of the 0%, 25%, 50%, 75% and 100% extract aqueous concentration,respectively. Germination percentage were determined at the end of the study. Individual cowpeas seedlings were planted in 4.5 litres plastic pots containing soil and irrigated with different amount of eucalyptus fresh shoot litter extracts (25g, 50g, 75g, 100g) and 500ml of distilled water. The treatments were replicated five times and the pots laid out in a completely randomized design in the glasshouse. Data on shoot height and 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 the shoot litter of E. saligna has both inhibitory and stimulatory effects on Vigna unguiculataat differentstages of plant growth and development. Seed germination decreased with increasing concentration of shoot extracts from 25%, 50%, and 75% to 100% even though there were no significance differences among treatments. Shoot heights, leaf number, leaf area, shoot and root dry weights, total chlorophyll increased significantly with increasing fresh shootextract aqueous concentration. This research data can be used to inform agriculturist, farmers, policy makers and advisers on the consequences of E. saligna in the agroforestry programmes. Further, the results can be used at an advisory level to inform efficient and effective use in the agroforestry systems to improve crop bioproductivity for increasing population in the world.