Differential Infection Dynamics of <i>Verticillium dahliae</i> in Dicotyledonous (Cotton) Versus Monocotyledonous (Maize) Host Systems

<i>Verticillium</i> <i>dahliae</i>, a soilborne fungal pathogen, infects and causes wilt symptoms in dicot but not monocot plants. The precise sequence of events when <i>V</i>. <i>dahliae</i> infects monocots remains unclear. In this study, we confirmed on several different hosts that <i>V</i>. <i>dahliae</i> can cause typical Verticillium wilt symptoms on dicots but not on monocots. Scanning electron microscopic and transmission electron microscopic studies indicate that <i>V</i>. <i>dahliae</i> germinates, expands, and initially penetrates both cotton (dicot) and maize (monocot) roots. While <i>V</i>. <i>dahliae</i> has been previously shown to colonize the root cortex in monocots, our work clearly revealed that the pathogen penetrates into the xylem but is unable to survive in the maize roots during early stages of colonization. Rather, the conidia and mycelia break down in maize, and remains of shrunken cells persist in the roots. Collectively, our results provide new clues on the sequence of events that occur when <i>V</i>. <i>dahliae</i> infects monocots versus dicots and may underlie Verticillium wilt symptoms on dicots but not on monocots.