Hyphal Interactions and Antagonism Among Field Isolates and Single-Basidiospore Strains ofAthelia (Sclerotium) rolfsii

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Abstract
Seventy-two field isolates of A. rolfsii [Sclerotium rolfsii] from 19 plant hosts and 15 geographical areas were paired in culture in all possible combinations. On the basis of antagonism zones (also called barrage zones) that developed in 86.5% of these pairings, the isolates were assigned to 25 interaction groups (i-groups). Within an i-group, all of the isolates grew together when paired and the hyphae intermingled with little or no cell death. In pairings between members from any 2 groups, antagonism zones developed; this was accompanied by the plasmolytic killing of hyphal cells. Isolates within a given i-group varied in morphological characteristics and frequently were isolated from different hosts or geographical areas. Anatagonism zones also developed in 80-92% of sibling pairings and in 86% of non-sibling pairings among 50 single-basidiospore (S1) strains obtained from 5 parent field isolates from California [USA] that belonged to i-group 1. Similar antagonism zones developed in all pairings between the S1 strains and these field isolates. Formation of antagonism zones in sibling and non-sibling pairings was not significantly influenced by media or by different incubation temperatures. The implications of these findings are discussed relative to similar observations reported for wood-decaying basidiomycetes.