REBEKKA POHL, ELKE FISCHER, RAINER SCHULTZE-KRAFT
University of Hohenheim, Institute of Plant Production and Agroecology in the Tropics and Subtropics, Department of Biodiversity and Land Rehabilitation, Germany
Species of the tropical genus Brachiaria are widely used in improved pastures. Field observations with the particularly widespread Brachiaria brizantha cv. Marandu indicate that it can be difficult to establish and maintain mixtures with a legume. Furthermore, in grass-only pastures complete lack of seedling recruitment has been observed. A reason for both phenomena could be allelopathy.
To elucidate the allelopathic potential of B. brizantha cv. Marandu in comparison with three other Brachiaria cultivars of current economic importance, B. brizantha cv. Toledo and the Brachiaria hybrids Mulato and Mulato II, two laboratory bioassays were conducted with aqueous extracts, in different concentrations, from (1) leaves and (2) roots of the four cultivars, testing their effect on (1) the grasses themselves (autotoxicity test) and (2) three forage legumes, Leucaena leucocephala, Desmodium ovalifolium, and Pueraria phaseoloides.
The autotoxicity test showed germination inhibition and a retarded seedling growth in the treatments with cvv. Marandu and Toledo. This could be caused either by allelopathic effects or the high osmotic potential of the extract solution. In the test with the legumes, aqueous leaf extract of cv. Marandu showed faint but not significant effects such as germination inhibition, reduced weight and root length of seedlings of D. ovalifolium and L. leucocephala. In contrast, low concentrations of cv. Marandu extract had beneficial rather than harmful effects on seedling growth of L. leucocephala. Similar observations of growth stimulating effects of allelochemicals in low concentrations are reported for other species.
The findings confirm the allelopathic potential of Brachiaria brizantha cv. Marandu. However, further research is needed to elucidate the complex issue of allelopathy within the genus Brachiaria. Such research should include (1) work in pastures where alleged allelopathy has been observed as well as (2) a comprehensive participatory survey in order to complement the rather anecdotic information available so far.
Keywords: Allelopathy, Brachiaria, Forage grass