MYCOHERBICIDES FROM CONSORTIUM CULTURE OF RHIZOSPHERE FUNGAL ISOLATES: EFFECTS ON SOIL CHEMICAL AND BIOLOGICAL PROPERTIES

Abstract

The quest for organic replacement for chemical herbicides has attracted attention from researchers over the past two decades owing to the deleterious effect of chemical herbicides on soil properties. This study investigated how mycoherbicides affected soil chemical and biological properties. Some metabolites were produced from consortium culture of fungal isolates obtained from rhizospheres of Panicum maximum, Ipomoea involucrata and Amaranthus viridis. The isolates were co-cultured using Czapek broth, and incubated for 28 days. The consortium combinations were: 1 - Aspergillus welwitschiae and Trichoderma hamatum, 2 - Aspergillus welwitschiae and Aspergillus aculeatus, and 3 - Aspergillus aculeatus and Trichoderma hamatum, with glyphosate as the control. Five millilitres (5 mL) of the crude extract containing 200, 400, 800 and 1600 mgL^-1, respectively, was added to experimental pots containing weeds of interest (Panicum maximum or Ipomoea involucrata) for 6 weeks in the screenhouse. The soils were evaluated for pH, soil organic carbon (SOC), total nitrogen (TN), available phosphorus and soil biological indicators like microbial respiration, soil microbial biomass carbon (SMBC), total heterotrophic bacteria and fungi (THF and THB). Results showed that combination 2 increased SMBC by 290% while combination 3 increased SOC from 1.87% to 3.04%. Available phosphorus uptake in combination 3 was 15.61%. There was a reduction in TN from 1.42 gkg^-1 to 0.91 and 0.94 gkg^-1 for consortia 1 and 2, respectively. The mycoherbicides stimulated the growth of THF at a rate of 0.96 fungi/week (p ≤ 0.05). It was concluded that mycoherbicides hold beneficial effects on soil biological and chemical properties.