Germination and seedling growth of groundnut seeds infected with Macrophomina phaseolina isolates

Abstract

Macrophomina phaseolina is a common contaminant of groundnut (Arachis hypogaea L.) seeds but not much information has been documented about its adverse impact on seed health and germination. This study was carried out to determine the incidence of M. phaseolina on groundnut (Arachis hypogaea) seeds displayed for sale in local markets, characterize the isolates and determine how the fungal presence would affect the germination and seedling growth, so as to provide information on seed handling practices and planning strategies for reducing crop loss due to the fungus. The fungus was isolated using the direct plating inoculation method and then grown for a period of 7 days on a potato dextrose agar (PDA) with temperature set at 28 oC. The DNA was extracted from pure cultures and PCR was performed using primer in pair: ITS4 and ITS5. The products got from the PCR were sequenced for identification of species on the National Centre for Biotechnology Information (NCBI) database. Phylogenetic tree was generated based on the ITS1-2 gene sequences of the isolates. The 18 M. phaseolina isolates adopted for use in this study were all obtained from apparently healthy seeds of different varieties of groundnut sourced from local markets in Delta and Edo States, Nigeria. The experiment on germination of groundnut seeds was set up in a completely randomized design in ten replicates. The individual M. phaseolina isolates inhibited germination and seedling growth in varying degrees. The virulence of the isolates ranged from moderately pathogenic (50%) to extremely pathogenic (75%). Out of the 18 isolates, 14 were found to cause 100% mortality. The inoculated plants exhibited the disease symptoms (damping off, root rot, collar rot, necrosis, wilting and chlorosis) while the control remained healthy. Seedling emergence, number of leaves, root length, and stem girth of infected plants decreased when compared to the control.