Sclerotinia key and images

Sclerotinia Fuckel
Type genus of the family Sclerotiniaceae.Type species: Sclerotinia sclerotiorum (Lib.) de Bary. Apothecia cup-shaped to funnel-shaped to plane, brownish, stipitate, arising from distinct, free, tuberoid sclerotia with a carbonaceous rind (black) and medulla (white) without remnants of host tissue. Apothecial outer excipulum of globose to hexagonal cells. Ascospores hyaline, ellipsoid, unicellular, multiguttulate. Macroconidial anamorphic state wanting. Terricolous or among herb debris of a number of vascular plants; apothecia in spring, summer or autumn.
Literature: Whetzel (1945), Kohn (1979), Holst-Jensen & Schumacher (1994), Graf & Schumacher (1995), Vaage (1996), Holst-Jensen & al. (1997b), Holst-Jensen & al. (1998).

1. Sclerotia lenticular to tuberoid, 2-8 x 1-4 mm, developing in leaf sheets and on culm remnants of grasses. Apothecia cup-shaped to plane, arising solitary or in groups from a sclerotium, disc 2-7 mm diam., stipe 2-17 x 1.1.5 mm. Asci 175-240 x 9-13.5 um. Ascospores ellipsoid, with pointed ends, thick-walled, 14-21 x 6-9 um. Apothecia produced in autumn. On a variety of host genera, most frequently on Poa spp. and Festuca spp. . . . . . Sclerotinia borealis Bub. & Vleug. (= Myriosclerotinia borealis (Bub. & Vleug.) L. M. Kohn)

1. Sclerotia tuberoid, developing in herb debris or among roots of herbaceous plants . . . . . 2.

2 (1). Asci 4-spored . . . . . 3.

2. Asci 8-spored . . . . . 4.

3 (2). Sclerotia developing in last year stems of Rubus chamaemorus , embedded in moss carpets in bogs, cylindrical, 2-12 x 2-5 mm. Apothecia shallowly cup-shaped to plane, medium to pale brown, disc 2-6 mm diam., stipe 5-30 x 0.6-1.5 mm. Asci 80-105 x 12-14 um. Ascospores ellipsoid, slightly inequilateral, with minute internal polar guttules when fresh, 10-15 x 5.6-8.0 um, occasionally megaspores to 18-22 x 8-11 um are observed. Apothecia in early summer . . . . . Sclerotinia tetraspora Holst-Jensen & T. Schumach.

Apothecia of Sclerotinia tetraspora arising from a sclerotium developed inside the culm of a Rubus chamaemorus plant, embedded in Sphagnum moss. Norway, Akershus, Eidsvoll, Frilsetåsen, June 17th. 1996. (Photo: © Arne Holst-Jensen)

Axenic culture of Sclerotinia tetraspora grown on PDA (potato dextrose agar) for 12 weeks at 20 C in darkness. (© Photo: Arne Holst-Jensen)

3. Sclerotia developing on the leaf base of Ranunculus glacialis, tuberoid, cylindrical, 2.5-15 x 2-8 mm. Apothecia cup- to disc-shaped, brownish orange, brick red to henna brown, up to four from each sclerotium, cup (disc) 2-10 mm diam., stipe 1-15 x 0.5-1.5 mm. Asci 130-150 x 7-12 um. Ascospores ellipsoid, slightly inequilateral, uni- (bi-) nucleate, 22-27 x 8-10 um. Apothecia in summer. . . . . Sclerotinia glacialis F. Graf & T. Schumach. The species is known only from Grisons, Switzerland.

4 (2). Ascospores dimorphic in size, 4 larger spores 12-18 x 7-10 um, 4 smaller spores 9-13 x 6-7 um. Apothecia solitary or two to three from a sclerotium, 5-20 x 2-8 mm, disc 2-10 mm diam., cup-shaped to plane to recurved with a central depression, stipe 10-40 x 0.5-2 mm. Asci 150-240 x 9-14 um. Frequently on leguminous hosts, occassionally on non-leguminous hosts. Causing clover rot in fields. Apothecia in summer and autumn . . . . . Sclerotinia trifoliorum J. Erikss.

4. Ascospores monomorphic . . . . . . 5.

5 (4). Sclerotia tuberoid, very variable in shape and size, 4-25 x 2-10 mm x 5-15. Ascospores uniform in size, 9-13.5 x 4-6 um, binucleate. Apothecia solitary or several from each sclerotium, disc 2-10 mm diam., when mature plane or recurved with a central depression, stipe 4-30 x 0.5-2 mm. Apothecial outer (ectal) excipulum composed of slightly elongated prosenchymateous cells turning out perpendicular to the apothecial surface. Asci 110-150 x 6-10 um. On a wide range of host plants (> 350 species among 60 plant families). Apothecia in spring or high summer . . . . . Sclerotinia sclerotiorum (Lib.) de Bary (= S. ficariae Rehm)

5. Sclerotia tuberoid or irregularly shaped, 0.5-2 mm diam. Ascospores uniform in size, 8-17 x 5-7 um, tetranucleate. Apothecia one from each sclerotium, disc 2-9 mm diam., applanate or recurved with a central depression when mature, stipe 1-4 x 1-2 mm. Asci 125-180 x 7-11 um. Apothecia in high summer. . . . . Sclerotinia minor Jagger. The species is not known from the Nordic countries.