Short CommunicationUse of quantitative PCR to understand within-host competition between two entomopathogenic fungi

Interactions between the entomopathogenic fungi Zoophthora radicans and Pandora blunckii infecting larvae of Plutella xylostella were investigated. This is the first report to quantify within-host growth of one fungus in the presence of another competing for the same host resource using quantitative PCR (qPCR) at regular time points during the infection process. In larvae inoculated only with Z. radicans, there was a cumulative increase in the quantity of Z. radicans DNA throughout the time course of infection. However, in dual-inoculated larvae, there was an initial accelerated rate of growth of Z. radicans compared to when it was inoculated alone, but by the time of host death it had been effectively excluded by P. blunckii. The implications of these results for co-existence of these fungal pathogens in the field are discussed.

Changes in quantities of Zoophthora radicans DNA (NW250) in single (T1 ■) and dual-inoculated with Pandora blunckii (T2 and T3 □) Plutella xylostella larvae during the time course of infection. Numbers in brackets represent the dose (conidia mm−2) of the pathogen (or pathogens) used in that treatment. Zr = Z. radicans, Pb = P. blunckii.Highlights► Within-host growth of Z. radicans in the presence of another competing fungus was measured with qPCR. ► Z. radicans accelerated its growth rate as a response to the presence of the competitor. ► Although the competitor practically excluded Z. radicans some DNA remained allowing co-existence.