Infection and temporal development of mycelium of <i>Albugo Candida</i> in cotyledons of four <i>Brassica</i> species

Abstract

Cotyledons of four Brassica species were inoculated with zoospores of Albugo candida produced from germinating oospores or zoosporangia. The sequence of events in mycelial development appeared to be the same from both types of inoculum. Up to the time of formation of the first haustorium there appeared to be no difference in the infection process in susceptible (B. juncea, B. campestris), moderately susceptible (B. hirta), and resistant (B. napus) hosts. At 2–3 days after inoculation, growth in B. napus ceased and a marked encapsulation formed around each single haustorium. In the other hosts mycelial development increased rapidly after the formation of the first haustorium. Up to 14 haustoria were observed in a single mesophyll cell. Encapsulations were rarely observed around haustoria in susceptible tissue. The massive amount of fungal thallus tolerated by the susceptible hosts emphasizes the highly specialized type of parasitism evolved by A. candida.