EXPLORING DIFFERENTIAL INTERACTION BETWEEN RHIZOCTONIA SOLANI ISOLATES AND HOST GENOTYPES IN THREE PATHOSYSTEMS
JHM SCHNEIDER1,2, PHJF VAN DEN BOOGERT2 and W HEIJBROEK1
1Institute of Sugar Beet Research (IRS), PO Box 32, NL-4600 AA, Bergen op Zoom, The Netherlands; 2DLO-Research Institute for Plant Protection (IPO-DLO), PO Box 9060, NL-6700 GW Wageningen, The Netherlands
Background and objectives
The aim of our study was to assess whether a reported statistically significant interaction between AG 2-t isolates and tulip genotypes in greenhouse experiments  indicated an isolate by genotype interaction, with the possible implication of physiological races within AG 2-t, or an interaction induced by environmental factors. In addition, interactions between AG 2-2 isolates and sugar beet genotypes and between AG 3 isolates and potato genotypes were explored statistically.
Results and conclusions
A statistically significant interaction between five R. solani AG 2-2 isolates and five sugar beet genotypes in one greenhouse experiment was found (ANOVA, P=0.001). Further analysis of the isolate by host genotype table showed differential interactions. However, reciprocal interactions did not occur in this experiment. A statistically significant interaction was also found (ANOVA, P=0.001) for five R. solani AG 3 isolates and six potato genotypes and reciprocal differential interactions occurred. Isolate 3R3, for example, had a DI of 54 for one potato genotype V and 72 for another genotype D on a scale of 0 to 100, whereas isolate 3R9 had a DI of 79 for genotype V and 54 for genotype D.
In conclusion, differential interaction of AG isolates to genotypes does occur in the three pathosystems studied, although it cannot yet be completely elucidated. The most aggressive isolates can be used for breeding purposes. Extremes in aggressiveness between isolates can be used for the study of mechanisms of interactions. In all three pathosystems partial resistance of some host genotypes was found. Partial resistance is often polygenically determined and sensitive to environmental conditions. Differential interaction of isolates has its implications for the development of detection methods for these specific isolates.