Dichotomous table for gallers on Hordeum

by Hans Roskam

1a On above-ground parts => 4

1b On roots => 2

2a Galls are distinct swellings =>3

2b Roots outwardly not markedly galled, tissue of infected sites containing ‘giant cells’. Developing females erupting from the root bark, occupy it for a while like poppy-seed sized cysts, at first white, then yellowish, eventually brownish. On cultivated barley and close relatives. Hordeum spp.: Heterodera avenae

= Oblong expanded, weak root thickenings on barley predominantly at the tips caused by the partially free-living meadow eelworm Pratylenchus pratensis have been reported.

= From the second half of the summer apterae of the aphid Tetraneura ulmi live on the roots of various grasses, incl. Hordeum.

3a Roots often with many broad swellings, half screw-like curved spindle-shaped, 0.5–6 x 0.5–5 mm. Hordeum spp.: Subanguina radicicola

3b Galls slender spindle-shaped, not curved screw-like. H. vulgare: Meloidogyne hapla

= Furthermore there are records of the occurrence of other Meloidogyne species. The galls of these species are usually thicker and larger than those of M. hapla and never have lateral roots, which is characteristic for M. hapla.

4a On inflorescences or flowers => 12

4b On tips of younger or older shoots, on culms or leaves => 5

5a Malformations on shoot tips caused by dipteran maggots => 9

5b Malformations caused by aphids or eelworms => 6

5c Long conspicuous stripes on chlorotic leaf tissue caused by rust fungus. H. bulbosum, distichon: Puccinia striiformis

5d Infected stems at first developing quickly, later on stunted, often remaining sterile, extensively covered with brown-black patches with spores. H. secalinum: Tranzscheliella hypodytes

6a Malformations by aphids => 8

6b Malformations by eelworms => 7

7a Plant compact, especially thickened at base. Leaves curled, sometimes undulate at margin. H. vulgare: Ditylenchus dipsaci

7b Young leaves folded and rolled, the sheaths at base sometimes slightly thickened. Hordeum spp: Anguina tritici

8a Leaf sheath swollen and discoloured, leaf blade ± spirally rolled. Aphid 2.0–2.75 mm long, oblong, olive-green, reddish close to the short, slightly swollen siphunculi. H. distichon, murinum incl. subsp. leporinum, vulgare: Rhopalosiphum padi

8b Similar malformations: H. murinum, vulgare: Diuraphis noxia

8c Also as an inducer of gall-like malformations on shoots. H. murinum, vulgare: Sitobion avenae

9a Malformations caused by fly maggots, which are situated at the shoot tip; maggots with buccal hooks => 11

9b Malformations caused by midge larvae, which reside in galls on culms in developed plants or live between leaf sheaths in young plants. Larvae without buccal hooks, but with sternal spatula => 10

10a Culm underneath the slightly swollen leaf sheath usually below the final node with several rimmed depressions, ca. 10–12 mm long, elongated, saddle-shaped, at the ends. Each gall containing a bright red larva. H. vulgare: Haplodiplosis marginata

10b Shoots of excessively leaf-like young plants with slender onion-like swelling at base. Leaves initially more erect, darker green, shorter and broader than in healthy plants; central leaves yellowing later and dying off. Later in development, shoots on first and second node with weak swellings. Culm here buckling easily. Underneath the sheaths are several 3–5 mm long, whitish-greenish larvae or flax seed-like brown puparia. H. vulgare: Mayetiola hordei

= Mayetiola destructor is also found on barley, but is far less common than on wheat or rye.

11a Growth of young plants stunted; axis of shoot shortened; inner leaves yellowed, outer ones remaining green. H. murinum: Oscinella frit

11b Similar damage might also be caused on same host by: Delia coarctata

11c On young plants the shoot tip is shortened and sometimes slightly thickened, cigar-shaped. At the terminal bud is an oblong cavity containing a maggot or a brown-yellow puparium up to 7 (9) mm long, yellowish- to greenish-white, weakly flattened, parallel sided. H. distichon, murinum, vulgare: Chlorops pumilionis

12a Malformations predominantly in ovaries or fruits of single flowers, only rarely in other parts; galls caused by smut fungi or eelworms => 16

12b Malformation of axis of inflorescence, expanded parts of the inflorescence or many parts of several single flowers => 13

13a Expanded parts of ± stunted inflorescence greened or leaf-like. Mite galls => 15

13b Malformations mainly on axis of inflorescence => 14

14a On dwarfed plants the axis of the inflorescence, which is usually hidden in the leaf sheath, is largely atrophied and bent, stair-like. H. murinum, vulgare: tarsonemid mite

14b Developing plants remain shorter. Terminal leaves clustered, yellowish or also normally coloured, basally slightly curled, sometimes appearing broadened and thickened. Above the upper node of the undeveloped culm are long yellowish- to greenish-white maggots or brown-yellow puparia, up to 7 (9) mm long. H. distichon, murinum, vulgare: Chlorops pumilionis

15a Spike severely stunted, hardly 1 cm long. From the basal part and also from the upper culm new nodes develop, up to 13 cm long with leaf-like shoots and rolled leaves. H. murinum: Unidentified gall mite

15b Several to many flowers of the spike greening and becoming leaf-like. H. murinum, vulgare: Aceria tenuis

16a Malformation by smut fungi of all flowers of a spike => 17

16b The infected ovary develops into a reduced, black-brown, thick-walled grain, containing many eelworms. H. vulgare: Anguina tritici

17a The fungus usually infests all ovaries of a spike and destroys them early, covering completely with dusting of spores during sporulation => 18

17b The sori are not completely covered by dusting of spores, but remain enclosed by the glumes. Usually all spikelets of spike are diseased. On cultivated barley and related species during maturation of grain. H. distichon, spontaneum vulgare: Ustilago hordei

18a Spores not foul-smelling, smaller => 19

18b On cultivated barley. Spore mass dark violet-brown, spores globular, 20–24 µm large or egg-shaped to rotund-oval 22–28 x 18–22 µm; with high reticulate pattern at surface. H. bulbosum, marinum, murinum incl. subsp. leporinum, vulgare: Tilletia controversa

19a Usually the diseased plants develop faster than the healthy ones, resulting in smut-infected spikes surmounting healthy ones. Spores globular to oblong-oval, The spores are solitary, long-oval, 6-9 µm long, yellowish brown, darker at one side; wall scattered finely echinulate H. distichon, jubatum, murinum subsp. leporinum, vulgare: Ustilago nuda

19b Spores smaller, c. 6 µm long, olive brown when ripe; then the spores are lighter at one side; wall spinulose. H. ? distichon, murinum, vulgare: Ustilago avenae

= The gall midge Sitodiplosis mosellana with orange larvae, lives in yellow-spotted, sterile spikelets on H. vulgare, destroying grain. The midge is very harmful but does not induce galls

mod 30.iii.2020