Dichotomous table for gallers on Agrostis

by Hans Roskam

1a Malformations of parts above ground => 2

1b Roots with only, crooked to screw-shaped, twisted swellings several mm long. A. capillaris, stolonifera: Subanguina radicicola

1c Roots are abnormally short and strongly bushy branched with half a mm large, initially white, later yellowish brown to dark brown elliptic bodies, cysts, attached. Agrostis spp.: Punctodera punctata

2a On inflorescences, flowers or fruits => 17

2b On shoots, stems or leaves => 3

3a Leaves or stems with expanded malformations => 13

3b Locally ± restricted malformations caused by animal parasites or young plants extensively disfigured => 4

4a Stems or leaves with locally restricted galls => 8

4b Expanded malformations on young plants, on stems or on shoot tips => 5

5a Young plants extensively stunted and disfigured => 7

5b Shoot tip stunted; leaves accumulated tuft-like, ± curled => 6

6a Terminal parts of stolons, and shoots transformed into tuft- to spadix-like (club-like) clustering of leaves. Axis of shoot shortened. Leaf sheaths swollen, fitted into one another; leaf blade withered, often reddened, ± wrinkled at base. Containing aphids between the sheaths. A. capillaris, stolonifera: ? Diuraphis holci

6b Shoot tip stunted. Leaves tuft-like accumulated, sheaths enlarged. Containing a single larva. A. gigantea, stolonifera: Tetramesa sp.

7a Young plants severely stunted, sometimes with additional tillers. Shoots at base ± slender spongy onion-like swollen, leaves short, ± thickened and curled. A. stolonifera: Ditylenchus dipsaci

7b Young plants with stunted development; often not producing seeds; shoots appearing slender club-like thickened at base. A single or several yellowish-white maggots inside, about 4 mm long. A. capillaris, stolonifera: Oscinella frit

7c Mainly from A. capillaris, with similar biology, has been recorded the closely related Oscinella nitidissima

8a On leaf sheath or -leaf blade, sometimes concurrently also on the axis => 11

8b Malformations exclusively on stems => 9

9a Stem ± stunted and locally swollen on all sides => 10

9b Stem below the sheath, often above the last node with an expanded weak, black coloured depression, containing an orange-yellow to brick-red larva. A. capillaris: Hybolasioptera fasciata

9c Base of a stem contains a whitish, 4 mm long larva between leaf sheath and the culm, just above a node. Externally hardly anything is visible. A. capillaris, stolonifera: Mayetiola agrostidis

9d One to three larvae live within the leaf sheaths, each in a depression of the stem. Basal part of the stem very weakly swollen. A. stolonifera: Mayetiola agrostivora

10a Stem swollen on all sides at different positions on the internodes; galls sometimes discoloured purple-red. Larval chamber in pith, the eventual exit hole in the lower part. A. canina, capillaris, gigantea: Tetramesa

10b Whitish to yellowish patches, which enclose the stunted shoot in a collar, usually over some distance, so inhibiting further development of shoot. A. canina, capillaris, gigantea, stolonifera: Epichloë baconii

10c Shoot axis stunted. Spikelets ± bleached. A. capillaris: cf. Oscinella frit

11a Galls on leaf blades, only a few mm broad, spindle-shaped to oblong cylindrical => 12

11b Leaf sheaths often markedly shortened, locally swollen and transformed into a single-chambered, purple gall, 5–10 mm long, 1–2 mm wide. Containing a single larva. A. capillaris: Tetramesa sp.

12a Leaf blade, usually close to base, occasionally in mid- or apical part, rarely also on shoot- and inflorescence-axis, with galls that are at first yellow-green, then often deep purple-red, ± spindle-shaped to cylindrical, about 1–3 (5) mm broad and 2 mm to even 25 mm long, large galls usually with a longitudinal furrow. A. capillaris: Subanguina graminophila

= As for the subsequently reported eelworm, spermogonia of the sac fungus Dilophospora alopecuri occur simultaneously in the galls. This fungus, apparently distributed by the eelworm, does not participate in gall formation because the gall is replenished with fruiting bodies of the fungus after it has already been vacated by the eelworms.

12b Similar leaf galls, sometimes up to 50 mm long, and, occasionally also in similar swellings of stems or inflorescences. A. canina, capillaris, gigantea, stolonifera: Anguina graminis

13a Malformations caused by animal inducers => 16

13b Malformations caused by parasitic fungi => 14

14a Leaves or stems with expanded patches of black-sporulating fungi => 15

14b Leaves of infected plants rolled inwards, strongly thickened, brittle, at first pale, then dark brown, eventually frayed and releasing reddish-brown oospores. Inflorescences stunted, or when emerged ± leafy. A. stolonifera: Sclerospora graminicola

15a Black stripes on leaves caused by smut. Spores single. A. canina, capillaris, stolonifera: Ustilago striiformis

15b Black stripes on leaves and stems. Spores in clusters of 2–8 sometimes with a several layered envelope of conspicuously small, sterile, cells. A. capillaris, stolonifera: Urocystis tessellata

15c The above-ground parts of the plant are disfigured, the hair roots are swollen; each contains 1‒10 ovoid, double-walled resting sporangia. Agrostis spp.: Olpidium agrostidis

16a Internodes with erineum- or crust-like, small proliferations usually below the sheaths soon browned. A. gigantea: ? Tarsonemus sp.

16b Stem poorly developed, with the upper parts especially shortened, undulately bent; panicles stunted, disfigured; remaining covered by the slightly swollen sheath. A. gigantea: ? Tarsonemus sp.

17a Malformations predominantly restricted to a few or many ovaries of the panicle; other parts only secondarily attacked => 21

17b Panicles completely disfigured or disfigured over substantial parts => 18

18a Axial parts of panicle stunted; spikelets more densely clustered, ± greened or discoloured; glumes not galled => 19

18b Spikelets enlarged, thickened, often violet, often whitish at base and apex. Glumes normal. A. canina, capillaris: Dendroptus krameri

19a Inflorescence ± stunted; flowers greened to varied extent or, in case of strong infestation, ± twisted and discoloured => 20

19b Axis of inflorescence stunted; panicle strongly curled. A. capillaris:
Unidentified eelworm

20a Flowers conspicuously greened by parasitic eelworms. Axial parts bent, glumes normal, spikelets yellowing if heavily infected or even bleached. A. capillaris, stolonifera: Unidentified eelworm

20b Spikelets ± greened or bleached, depending on degree of response of host and infestation. A. capillaris, stolonifera: Aceria tenuis

21a Ovary temporarily gall-like swollen often in all flowers, soon filled with a brown-black foul-smelling spore mass; developing ± globular, compact smut body between the often strongly spreading glumes. Inflorescence having a squarrose appearance. Agrostis spp.: Tilletia sphaerococca

21b Ovary conspicuously swollen and elongated, transformed into a ± slim bottle-shaped, gall later on usually discoloured purple. Containing many eelworms. Glumes greatly enlarged. Agrostis spp.: Anguina agrostis

mod 30.iii.2020