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

Cowpea ( Vigna unguiculata ) is a nutritious leguminous crop cultivated by many smallholder farmers in developing countries of the world. Fusarium spp. and fumonisin B 1 (FB 1 ) are known to be associated with cowpea seed. This study was performed to determine the phytotoxic effects of FB 1 on cowpea seedlings and to provide insight on the effect of the toxin on ceramide synthase gene expression. Surface-disinfected seeds were imbibed in FB 1 solutions of 5, 20 and 40 mg/L concentrations. Additionally, seeds were artificially inoculated with three different FB 1 -producing Fusarium verticillioides strains. Percentage emergence was reduced by all three FB 1 concentrations and seeds inoculated with F. verticillioides strain MRC 8265. Seedlings imbibed in 40 mg/L FB 1 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 FB 1 concentrations when compared to the controls. To evaluate the effect of FB 1 on ceramide synthase gene expression, seeds were imbibed in a 20 mg/L FB 1 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 FB 1 did not influence ceramide synthase gene expression in cowpea. Although FB 1 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.