Rhizoctonia disease of tulip : characterization and dynamics of the pathogens

<p>Rhizoctonia disease causes severe losses during the production cycle of tulip. The complex nature of the disease requires a precise characterization of the causal pathogens. Typical bare patches are caused by R. solani AG 2-t. Bulb rot symptoms are, apart from AG 2-t isolates, caused by R. solani AG 5. AG 4 isolates seem of little importance in field-grown tulips.</p><p>Anastomosis behaviour showed AG 2-t to be a homogeneous group, closely related to the heterogeneous group of AG 2-1 isolates. Pectic enzyme patterns discriminated tulip infecting AG 2-t isolates from AG 2 isolates not pathogenic to tulip. Geographically separated AG 2-t and AG 2-1 isolates, both pathogenic to tulip, differ in nucleotide number and sequence of ITS rDNA.</p><p>Differential interaction between AG 2-t isolates and tulip cultivars was highly influenced by experimental conditions. According to geostatistical analysis field sampling intensity could be reduced down to 10% and still provided adequate disease severity maps. Bare patches due to natural and artificial infestation declined during successive croppings of bulbs, whereas bulb rot tended to increase. Temporal niche differentiation is one explanation for the decline phenomenon.</p>