First report of Phomopsis subordinaria in a Natural Population of Plantago lanceolata L. in Southwest Finland

In August 2002, darkened and downwards turned flowering stalks were observed on plants of Plantago lanceolata in its natural habitat in the Ã…land Islands southwest of Finland. An estimated 10% of the P. lanceolata plants in a ca. 0.2 ha meadow displayed these symptoms. Stalks with sporulating fungal structures were collected for closer microscopic examination. The morphological characteristics of the conidiogenous cells, which were slightly broadened near the base, were similar to those of Phomopsis subordinaria (Desm.) Trav. as described by de Nooij & van der Aa (1987). Of the two described conidial types, alpha and beta, collected samples contained only α-conidia.

Twelve-week-old P. lanceolata plants were inoculated as described by de Nooij & van der Aa (1987). A suspension of P. subordinaria conidia was obtained by shaking a 2 cm piece of infected stalk in 30 ml of sterile water for 30 minutes at 250 rpm. Stalks were wounded just below the ear with a sterile needle, then brushed with the suspension of P. subordinaria conidia. Eight P. lanceolata plants were wounded and inoculated, and eight were wounded and brushed with sterile water to serve as controls in the experiment. Plants were kept in the greenhouse at 22/16 ˚C and 16/8 hr light period, respectively. After 2 weeks, darkening and bending typical of the stalk disease observed on P. lanceolata in the meadow was observed on 90% of the inoculated stalks. No symptoms were observed on the control plants. After 6 weeks the fungus had grown into the rosette of the wounded inoculated plants, causing severe wilting and eventually plant death.

The pathogen was reisolated from affected plants by incubating 5-mm pieces of wounded stalks on water agar in Petri dishes at 20 ± 3 ˚C. Conidia exuding from sporulating pycnidia were mass transferred onto potato dextrose agar (PDA) plates. After 7 days incubation, pycnidia with newly forming conidia were produced fitting the description of P. subordinaria.

There are reports of P. subordinaria infecting P. lanceolata in both Great Britain (Grove 1935) and in the Netherlands (de Nooij & van der Aa 1987). However, no previous record was found on the occurrence of P. subordinaria in natural populations of P. lanceolata in Finland. Diseased specimens of P. lanceolata have been deposited in the Herbarium at the University of Turku, Finland (accession number TUR 158521).