The effect of mycorrhizal (Glomus intraradices) colonization on the development of root and stem rot (Phytophthora vignae) of cowpea

Abstract

The effect of prior colonization of cowpea roots by the vesicular-arbuscular mycorrhizal (VAM) fungus, Glomus intraradices, on the detrimental effects on plant growth induced by the stem and root rot pathogen Phytophthora vignae was evaluated. VAM and non-VAM plants, inoculated by transplanting into soil with 0.1, 0.5, or 1.0%pathogen inoculum/soil (v/v), were evaluated for effects upon disease incidence after 2 wks of further growth. There were no shoot or root growth differences between VAM and non-VAM plants in the absence of the pathogen, because all plants were fertilized sufficiently. Reduction of shoot growth due to the disease was less on VAM plants, at the lowest (0.1%) pathogen inoculum level. Mycorrhizal colonization had no significant effect on root weight at any pathogen inoculum level. Stem and root disease severity were significantly lower only at 1.0% inoculum level, whereas percent root infection was lower at the 0.5 and 1.0% inoculum levels. Root colonization by the VAM fungus was reduced proportional to the pathogen inoculum level and amount of root infection. These results indicate that inoculation with G. intraradices could provide some degree of reduction of P. vignae stem and root rot disease on cowpeas, independent of nutritional or other growth effects.