Exploring differential interactions between Rhizoctonia solani AG 2-t isolates and tulip cultivars

Experiments were conducted to explore differential interaction of Rhizocton ia solani AG 2-t isolates on tulip cultivars in soil artificially infested under different experimental conditions. Comparison of residual variances o btained by analysis of variance and by analysis of additive main effects an d multiplicative interaction effects (AMMI) showed that open-air experiment s should be used for interpretation of isolate by cultivar interaction. In open-air experiments, variability was lower than in greenhouse tests. In th e biplot, derived after AMMI-analysis over isolates by years and by cultiva rs, isolates tended to occur in year clusters, indicating a differential ef fect of year on disease expression. Three isolates occurred in isolate clus ters, thus accounting for a significant year by isolate by cultivar interac tion. One cluster consisted of three isolates high in aggressiveness an all tested tulip cultivars, and another cluster consisted of three isolates lo w in aggressiveness. Greenhouse conditions and inoculum carrier significant ly influenced quantitative differential interaction patterns. Isolates grow n on oat kernels were more aggressive than those grown on autoclaved perlit e particles soaked in liquid malt peptone. Differential interaction of AG 2 -t isolates on tulip cultivars does occur, although it cannot yet be disent angled completely.