Earlier papilla formation and resistance to barley powdery mildew induced by a papilla-regulating extract
1994
Inoue, S. | Aist, J.R. | Macko, V.
Timing of papilla formation has been suggested to be an important factor for papilla-mediated resistance. Formation of oversize papillae and resistance to penetration attempts by the powdery mildew fungus have been reported to be induced in inoculated epidermal cells of susceptible barley coleoptiles by a partially purified, papilla-regulating extract (PRE) from healthy barley leaves. A time-course study was conducted to determine whether or not early papilla formation may be an important component of this PRE-induced resistance. Inoculated, susceptible barley coleoptiles were incubated on the PRE in a 10 mM Ca(NO3)2 solution. The timing of initiation and termination of cytoplasmic aggregates, initiation of papillae, initiation of fungal penetration pegs and initiation of haustoria were determined in vivo using differential interference contrast optics. On average, papilla formation was initiated 23-27 min earlier in the PRE treatment than in controls incubated without the PRE. An individual site-based analysis showed that PRE treatment of coleoptiles increased, from 23% to 68%, the frequency of earlier-formed papillae that fungal penetration pegs encountered when they were first detected. Thus, early initiation of papilla formation is a component of the PRE-mediated resistance to barley powdery mildew. However, since papillae in the PRE-treated coleoptiles were highly effective in preventing penetration regardless of their time of initiation, it appears that papilla content may be more important than earliness in determining their efficacy.
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