Pre-inoculation with Hyaloperonospora parasitica reduces incubation period and increases severity of disease caused by Albugo candida in a Brassica juncea variety resistant to downy mildew

Studies were undertaken to determine any interaction of an asymptomatic isolate of Hyaloperonospora parasitica (downy mildew) with a virulent isolate of Albugo candida (white rust) and Brassica juncea. White rust symptoms appeared 4 days earlier and were significantly more severe when a variety of B. juncea resistant to downy mildew but highly susceptible to white rust was first inoculated with A. candida followed 10 days later with H. parasitica. DNA extractions of tissues indicated H. parasitica had colonized the asymptomatic plants systemically. These are the first reports of (a) the systemic colonization by H. parasitica in a host resistant to downy mildew, and (b) the increase in susceptibility of a Brassica to white rust disease from asymptomatic colonization by H. parasitica.