Effect of fumonisin B1 on the emergence, growth and ceramide synthase gene expression of cowpea (Vigna unguiculata (L.) Walp)

Abstract

Cowpea (Vigna unguiculata) is a nutritious leguminous crop cultivated by many smallholder farmers in developing countries of the world. Fusarium spp. and fumonisin B1 (FB1) are known to be associated with cowpea seed. This study was performed to determine the phytotoxic effects of FB1 on cowpea seedlings and to provide insight on the effect of the toxin on ceramide synthase gene expression. Surface-disinfected seeds were imbibed in FB1 solutions of 5, 20 and 40 mg/L concentrations. Additionally, seeds were artificially inoculated with three different FB1-producing Fusarium verticillioides strains. Percentage emergence was reduced by all three FB1 concentrations and seeds inoculated with F. verticillioides strain MRC 8265. Seedlings imbibed in 40 mg/L FB1 had reduced seedling length whilst seedling mass was reduced by all treatments. Total chlorophyll content was higher in leaves of seedlings raised from seeds imbibed in all three FB1 concentrations when compared to the controls. To evaluate the effect of FB1 on ceramide synthase gene expression, seeds were imbibed in a 20 mg/L FB1 solution. RNA was extracted from untreated and treated samples after 0, 3 and 12 dpi with the latter being divided into shoot and roots samples. Semi-quantitative reverse transcription PCR suggested that there were no significant differences in ceramide synthase gene expression between the control and toxin treated cowpea samples. It thus appears that FB1 did not influence ceramide synthase gene expression in cowpea. Although FB1 exhibited phytotoxic effects on developing cowpea seedlings, the observed physiological and morphological changes were not a result of down regulation of ceramide synthase gene expression.