Evaluation of pathogenicity on cereal and potato of Fusarium spp. isolated from field of Solør area

Abstract

Fusarium Dry Rot (Fusarium spp.) caused by fungi from the Fusarium genus is a problem of great importance in Norwegian potato production. This thesis presents results from a study on Fusarium population present in agricultural soil of a specific area in Norway and their pathogenicity on potato (Solanum tuberosum), Oat (Avena sativa) and Barley (Hordeum vulgare). Soil sample were taken from Solør , an important potato production area . Recurrent postharvest losses attributed to Fusarium Dry Rot (FDR) have been observed despite the use of rotation between cereal and potato. The presence of particular Fusarium species able to sustain the rotation was hypothesized. Eight soil samples from 8 fields of different crop history were plated following a modified Warcup plate technique and incubated for 7 days at room temperature. After identification, 45 isolates belonging to 8 species were recovered with predominance of F.oxysporum, F.merismoides and F.avenaceum. Isolate of F.dimerum and F.venenatum two rarely isolated species in Norway as well as F.solani and F.sporotrichioides were also recovered. The pathogenicity of soil Fusarium species was evaluated. Two potato varieties of various resistances to Fusarium Dry Rot, cv. Asterix and cv. Mandel, were used in this experiment. Several pathogenicity tests were carried out and a modified method was established. Tubers were wounded, inoculated with a mycelium solution and incubated at 10°C for 4 weeks. Cv.Mandel tubers appeared to be more susceptible to Fusarium spp than Cv.Asterix. F.avenaceum and F.sporotrichioides were the two most aggressive species, causing significant increase of wound volume and the formation of cavities. Isolates of F.oxysporum and F.merismoides showed a rather weak pathogenicity as well as the other minor species recovered. A seed germination assay was carried out for evaluation of isolated Fusarium pathogenicity on cereal. The oat variety Belinda and the barley variety Habil were used for this experiment. Inoculum solution was prepared following a bubble breeding methods. Seeds were germinated in a petri dish filled with filter paper imbibed of mycelium suspension. After the second day the number of germinated seeds were assessed daily for a 5 day period and compared to an uninoculated control. The size of cotyledon was measured in the fifth day. F.avenaceum and F.sporotrichioides had a significant effect on germination rate for both cv.Belinda and cv.Habil reducing significantly the number of germinated kernel in comparison to the control. F.oxysporum were weakly pathogenic measured as germination rate but seemed to affect cotyledon size at the fifth day. The other Fusarium spp. affected only weakly the germination rate and the cotyledon size. Due to its pathogenicity on both potato and cereal as well as to be frequently isolated from fields F.avenaceum seems to be an important species responsible of symptom conservation over time in the field of Solør area.