Dichotomous table for gallers on Poa

incl. Ochlopoa

by Hans Roskam

1a On above-ground parts => 3

1b On roots => 2

2a Roots with several curved swellings, about 0.5-6 mm long, crooked or half screw-shaped. Ochlopoa annua, P. pratensis, trivialis: Subanguina radicicola

2b Poppy seed size, white to brown cysts, on outside of roots. Poa spp.: Heterodera avenae

3a Galls on inflorescences or their parts => 19

3b Malformations on vegetative parts => 4

3c Whitish, at surface yellowish or brownish patches, which envelope a large area of the upper part of stem, of which further development is stunted. Node of stem rarely swollen, encircled by fungus stroma, yellowish when mature; several nodes may be affected; flowering stunted; stroma contains narrow asci and filamentous spores. P. nemoralis, pratensis, stiriaca, trivialis: Epichloë typhina

4a Malformations on leaves or localised galls on culms => 6

4b Whole plant disfigured => 5

5a Plant withered all parts especially at base ± spongy, thickened. Ochlopoa annua, Poa trivialis: Ditylenchus dipsaci

5b Plant, especially culm, severely stunted; panicle bleached. Ochlopoa annua: Unidentified dipteran

6a Galls on culm => 10

6b Malformations on leaf blades and sheath => 7

7a Expanded malformations => 8

7b Leaf blade at base with oval or elongated bulge-shaped, usually dark violet swellings several mm long; occasionally occurring on leaf sheaths. P. nemoralis, palustris, pratensis: Anguina sp.

8a Leaf blades, partially also sheaths, with several long, parallel bleached stripes of smut, later on with dusting of spores. Fungus exceptionally also on panicle => 9

8b Leaf blade spirally rolled or twisted. P. nemoralis: Inducer unknown

9a Spores 1–2 (3) enveloped by a tight layer of sterile auxiliary cells. Poa palustris: Urocystis-poae-palustris

9b Spores similar, on other Poa spp., Ochlopoa annua: Urocystis poae

9c Spores single, without sterile envelope. Poa spp.: Ustilago striiformis species complex

10a Galls bulge-like or spindle- to club-shaped, glabrous or grooved => 12

10b Galls occupied with many rootlets, up to 10 mm long => 11

11a Stem in the middle or upper part of the culm above a node locally weakly swollen, with many, at first whitish, then pale brown rootlets, in longitudinal direction at either side of furrow, ± appressed to culm, protruding from leaf sheath. Larvae white, between the flattened shoot axis and leaf sheath. P. alpina, cenisia, nemoralis, pratensis, trivialis: Mayetiola graminis

11b Similar galls with development of closely crowded adventitious rootlets mostly on above-ground or subterranean nodes on culm; rootlets however not separated by longitudinal furrow, but irregularly growing in a tangled mass. P. nemoralis: Mayetiola radicifica

12a Less or more distinct spindle-shaped swellings on culm; containing larvae => 16

12b Larvae on culm underneath the often somewhat inflated leaf sheath => 13

13a Larvae in distinct depressions of culm, usually situated above the upper node => 15

13b Shoot axis weakly swollen above the second or third node => 14

14a The basal part of the stem, above the 2nd or 3rd node, is more or less swollen. Between the leaf sheath and the stem live here a variable number of white larvae, each in an oval shallow depression of the stem. Pupation within the gall, in a puparium. Larval spatula present, hastiformous. P. nemoralis, occasionally P. pratensis: Mayetiola joannisi

14b The basal part of the stem is more or less swollen. Larval spatula absent. Furthermore, see Mayetiola joannisi. P. pratensis: Mayetiola schoberi

15a Culm usually above the last node with elongated, one-sided, black-walled depression; containing a single larva. P. pratensis: Hybolasioptera fasciata

15b Culm above the last node with one or several slender, saddle-shaped rimmed depressions. Each containing a brick red larva. P. palustris, pratensis: Haplodiplosis marginata

16a Galls on P. palustris, bulbosa => 18

16b On P. nemoralis => 17

17a Grain-like swellings protruding from the sheaths, spindle-shaped, up to 5 mm long; at first pale green, then brownish, longitudinally grooved. Containing a single white larva: Tetramesa poae

17b Culm distinctly shortened; slightly spindle-shaped thickened above a node below the not spreading sheath; panicle remains covered by sheath. Containing a single larva: Tetramesa sp.

18a On P. palustris; weak, discoloured swelling on the shoot axis above the 3rd, 4th or 5th node: Tetramesa sp.

18b On P. alpina, bulbosa. Swelling up to 18 mm long, 2 mm broad above the first node below the panicle, protruding from the leaf sheath on one side. Tetramesa sp.

19a Malformations of spikelets => 21

19b Galls emerge from ovary => 20

19c Several larvae develop in inflorescences. P. pratensis: Contarinia floricola

= Ditto, mainly P. trivialis: Sitodiplosis cambriensis

20a Ovaries slender, bottle-shaped, enlarged, usually discoloured violet. Ochlopoa annua, Poa alpina, nemoralis, palustris, pratensis: Anguina agrostis

20b Similar galls; glumes sometimes conspicuously elongated. P. alpina, pratensis: Unknown eelworm

20c Infected ears and panicles appear normal. Since the larvae inside the flowers feed on the flowering parts they prevent seed formation. The result is wrinkled seed or sterile ears. P. pratensis: Dasineura poae

21a Spikelets leaf-like, not transformed into bulbils. Flowers thickened at base and ± reddened. P. bulbosa: ? Anguina sp.

21b Spikelets variously disfigured, often withering prematurely, with symptoms of bleaching. Poa spp.: Aceria tenuis and/or Aceria cornuta

mod 18.iii.2020