Evaluation of Competitive Ability of Petiveria alliacea L. and Tithonia diversifolia (Hemsl.) A. Gray in a Two-species Replacement Series Study in Ibadan, Nigeria

Abstract

Petiveria alliacea (Pa) is an invasive weed species that is spreading in the rainforest zone of Ibadan, Nigeria. This study investigated the dominance and competitive ability of Petiveria alliacea relative to Tithonia diversifolia (Td), another aggressive invasive weed species in the rainforest agroecological zon♂e. This competitive ability was assessed using four monoculture densities (1, 2, 4 and 8 plants/pot) and three mixture densities (1:1, 2:2, 4:4) of P. alliacea and T. diversifolia plants/pot, laid out in a Completely Randomised Design (CRD). Plant dry weight (PDW), Relative Yield (RY), Relative Yield Total (RYT), and aggressivity index were determined. Data were analysed using descriptive statistics and ANOVA at α = 0.05. The RY values of Pa and Td were 0.81 and 0.56, respectively, while RYT (1.37) exceeded unity, indicating a synergistic relationship. Pa showed positive aggressivity (0.06) over Td. The interspecific competition between the species at the three densities was more intense than the corresponding intraspecific competition. This implies that Petiveria alliacea outcompeted Tithonia diversifolia, which may be due to the deeper taproot system of P. alliacea compared with that of T. diversifolia. Therefore, farmers should discourage the establishment of Petiveria alliacea at high densities in their fields.