Plant Parasites of Europe

leafminers, galls and fungi

gallers on Rorippa

Dichotomous table for gallers on Rorippa

(incl. Nasturtium, Sisymbrella)

by Hans Roskam

1a On parts above ground => 3

1b On roots or on root collar => 2

2a Roots with expanded spindle- to barrel-shaped succulent swellings, ± bulging. “Clubroot”. R. austriaca, islandica, sylvestris: Plasmodiophora brassicae

2b Globular, pea- to cherry sized succulent galls on root collar, occasionally clustered. R. amphibia, islandica: Ceutorhynchus assimilis

3a On shoot tips, leaves, inflorescences or flowers => 6

3b Galls mainly or only on shoot axis => 4

4a Galls expanded, of very variable shape => 5

4b Axis with spindle-shaped, 10–15 (30) mm long, usually deep green swelling. Containing a single larva. R. amphibia: Ceutorhynchus chalybaeus

5a Youngest shoot parts swollen over ± extended length, soon covered with a loose, white down of branched conidiophores. R. amphibia, austriaca, islandica, palustris, sylvestris: Hyaloperonospora rorippae-islandicae

5b Young parts of non-flowering or flowering shoots with elongate bulges, at first glossy-white porcelain-like, later on with mealy dusting, sometimes coalescing into larger clusters, also curved swellings. Rorippa spp.: Albugo candida

6a On leaves, inflorescences or flowers => 8

6b On the tip of shoots, developing leaves or inflorescences => 7

7a Tip of main- and side shoots, also axial buds transformed into spongy, whitish, coalescing masses; the neighbouring, partially normally developed organs densely clustered, basal parts of petioles or flower buds variously swollen close to the gall. Sometimes the inflorescence galls are overtopped by some atrophied flowers. Containing several yellow- to orange-coloured larvae. R. amphibia, x anceps, austriaca, palustris, pyrenacia, sylvestris & subsp. kerneri: Dasineura sisymbrii

7b Longitudinal growth of axis stunted. Leaves or all parts of infected inflorescence clustered. All parts at base ± succulent, but not swollen and spongy, gall very variable. Containing several whitish- to lemon yellow, jumping larvae. R. palustris, pyrenaica, sylvestris: Contarinia nasturtii

8a On inflorescences or flowers => 13

8b On leaves => 9

9a Galls caused by animals => 12

9b Galls caused by fungi => 10

10a Sori white => 11

10b Leaves, also stem, with rotund, dull brown to black warts, or petioles with oblong, up to 1.5 mm long, bulge-like swellings; organs if strongly infected ± curved. R. amphibia: Physoderma vagans

10c On the same host the very similar punctiform, rotund, nodular protruding swellings on leaf blades or in flat brown bulges on petioles are attributed to Physoderma magnusianum

10d Small hard gregarious pustules, less than 0.5 mm across. Rorippa spp.: Synchytrium aureum

11a Leaf midrib, also stalks and venation, with spindle-shaped bulges. Leaf blade with ± rotund, pale green swellings. Sori at first closed, white and glossy, porcelain-like, then with dusting. Rorippa spp.: Albugo candida

11b Largely similar malformations, covered with loose down of conidiophores. R. amphibia, austriaca, islandica, palustris, sylvestris: Hyaloperonospora rorippae-islandicae

12a Basal leaves stunted. Midrib shortened, leaf blade ± nested, dark green, bent or rolled upwards. Strongly infected plants do not flower. R. amphibia: Aphis triglochinis

12b Leaves deflected over their top. Variously distorted and ± curled; sometimes the axis is stunted on one side and bearing several clustered disfigured leaves Rorippa spp.: Philaenus spumarius

13a Galls restricted to flowers => 15

13b Malformations on other parts of inflorescence => 14

14a Upper leaves disfigured. R. austriaca: Unidentified gall mite

14b Axis stunted. Flowers clustered, aborted. R. sylvestris: Aphis gossypii and/or Aphis nasturtii

15a Flowers unopened, often reddish discoloured on the outside, ± spongy thickened; stalk sometimes slightly elongated, resulting in a deflected gall. R. x anceps: Unidentified gall midge

15b Flowers swollen, ± egg-shaped, unopened. Corolla absent. Stamens short, thickened; ovary thickened. Containing several whitish- to pale yellow jumping larvae. R. palustris, pyrenaica, sylvestris: Contarinia nasturtii

Last modified 29.iv.2020