Induction of Resistance toErysiphe graminisf. sp.hordeiin Near-Isogenic Barley Lines

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Abstract
Inoculation of barley leaves with compatible or incompatible races of Erysiphe graminis f. sp. hordei protected leaves against subsequent infection by compatible races. When either compatible or incompatible inducer races were inoculated onto barley leaves and then removed at intervals, less than 1 hr of exposure to the inducer race provided significant protection against the challenge race. The resistance further intensified as the exposure time of the inducer race was increased to 6 or 9 hr. This early host response suggests that induction of resistance is initiated prior to appressorial penetration which occurs 6-8 hr after inoculation. Resistance was expressed as reduced numbers of colonies of the challenge race. Hence 6-9 hr of exposure to either a compatible or an incompatible inducer race reduced the number of mildew colonies produced by a compatible challenge race by 71-77%. There was no change in infection type. The protection increased with increasing inoculum density of the inducer race and lasted for at least 72 hr. Incompatible inducers races, which were not removed from the leaf prior to challenge inoculation, caused almost total protection against a compatible challenge race.