Occurrence of different Phoma lingam pathotypes on oilseed rape cultivars with different resistance gene background

Abstract: In the frame of a field study related to the artificial improvement of Phoma disease pressure, we monitored the disease incidence and severity of Phoma lingam on a small set of cultivars at a location close to Göttingen, central Germany. Visual assessments were performed on leaves, stems and the root collar. Furthermore, isolations were taken from diseased tissues. Isolates were differentiated into pathotypes by the use of the cotyledon test using the differential set Lirabon, Quinta, Glacier, Jet Neuf, Doublol (all of them rlm7) and Caiman (Rlm7).High disease incidences but moderate disease severities were recorded. Inoculated variants (conidia spraying, stubble deposition) showed no significant differences to controls. Control of Phoma stem canker by intense spraying of ERIA (ai: Difenoconazol, intervals of about 3 weeks) was always very effective and highly significant in all cultivars. Diseases severities displayed the superior field resistance of the Rlm7 cultivar Caiman compared to the other rlm7-cultivars tested.Phoma isolations were performed from cultivars Caiman and Oase. A number of 279 single pycnidiospore and hyphal tip isolates were checked in a first screen on cotyledons of cv. Lirabon to differentiate L. maculans (virulent on cv. Lirabon) and L. biglobosa (avirulent on cv. Lirabon). About 52 % of isolates were assigned to L. maculans. Significantly more L. maculans isolates originated from cv. Oase. L. biglobosa was predominant on cv. Caiman (about 96%). Race differentiation showed that diversity of Phoma-pathotypes was higher on cv. Oase than Caiman. Among the isolates originated from cv. Oase there were 9 avr7-isolates (3.3%) showing the presence of avr7 isolates in central Germany without a history of cultivating Rlm7 varieties.