Dichotomous table for gallers on Arabis

by Hans Roskam

A gallers on Arabis glabra (= Turritis glabra): see special key below

B gallers on other Arabis species => 1

1a On parts above ground => 3

1b On roots or root collar => 2

2a Roots with conspicuous, mostly all-sided, spindle-shaped to cylindrical, succulent compact swellings, up to 15 mm long, 8 mm broad. Inside the galls are many cells containing dense masses of minute spores. “Clubroot”. Arabis spp.: Plasmodiophora brassicae

= Two cyst-forming eelworms occur on Arabis species, viz., Heterodera schachtii and H. cruciferae

2b Root collar with one to several rotund succulent, one-chambered galls, up to 7 mm long, with a curved larva inside. A. alpina subsp. caucasica: Ceutorhynchus assimilis

3a On flowers or fruits => 16

3b On vegetative parts => 4

4a Malformations caused by fungi fruiting at surface => 13

4b Malformations by animal causers => 5

5a Malformations on terminal parts of shoots or on leaves => 6

5b Stem bulging especially close to ground, variously distorted, outside with single or several rimmed depressions containing a scale insect. A. collina, rosea: Planchonia arabidis

6a Malformations on single to many already ± developed leaves => 7

6b Developing shoots already stunted in the rosettes. Leaves not unfolding, shortened, spoon-shaped, with ± thickened veins; clustered, bud-like; gall more densely pubescent, up to about 6 mm long; occasionally enclosed by some spreading leaves, only thickened at base and ± abnormally pubescent or etiolated ± tuft-like side shoots. Larvae many, flesh-coloured to red. Mainly on A. albida, alpina subsp. caucasica, more rare on A. aubretioides, hirsuta, stelleri: Dasineura alpestris

7a Leaves folded, bulging or rolled at margin => 10

7b Leaves disfigured differently => 8

8a Leaves conspicuously clustered => 9

8b Rosette leaves stunted; stalk and basal part of midrib spongy, swollen, pale green: Ditylenchus dipsaci

9a Main- and lateral shoots terminally stunted, densely occupied by small leaves, transformed into branched, almost witches’ broom-like tufts. A. procurrens: Unidentified aphid

9b Leaves at base of thickened stem disfigured, less pubescent, enveloping the stem in a globular, whorled cluster. A. ciliata, hirsuta: Inducer unidentified

10a Leaf blades at margin rolled or with localised swellings; mite galls => 11

10b Leaf blades of many inner rosette leaves ± pod-like folded upwards, slightly thickened, brittle, pale green. Inside the silique are many white powdered, grey-green aphids. A. hirsuta, parviflora: Lipaphis rossi

= Similar malformations on Arabis have also been attributed to Brevicoryne brassicae

10c On upper sides of leaves, causing lateral parts of leaves to fold upwards towards midrib. A. alpina: Pseudobrevicoryne leclanti

11a Rolls or bulge-like swellings with abnormal pubescence => 12

11b Leaves partially yellowed; rolled at margin. A. pumila: Unidentified gall mite

12a Rosette leaves abnormal pubescent, usually curved upwards at margin. A. alpina: Unidentified gall mite

12b Leaves curled, ± rolled inwards or with irregular, sometimes violet-red swellings; infected areas more pubescent. A. hirsuta: Aceria drabae

13a Malformations caused by fungi with white fruiting bodies => 14

13b Shoot with ± distinct etiolations, sterile. Stem leaves thickened, disfigured, pale green, stunted; usually large areas on underside with small, scattered, red-brown telia. Arabis spp.: Puccinia thlaspeos

13c Rotund- to oblong, often coalescing, dark brown sori on the upper part of inflorescence, flower peduncles and siliques. A. pumila: Puccinia paulii

14a Sori consisting of loose, ± mealy down of branched conidiophores => 15

14b Sori dense, pad- or bulge-like, at first glossy, porcelain-like, dusty after rupturing; conidia in rows. On the underside of leaf blades rotund, on upperside sometimes violet-margined, rarely to distinctly swollen; on stem parts ± elongated spindle-shaped, often strongly swollen and curved. Arabis spp.: Albugo candida

15a Stem sometimes infected over large area, swollen, sometimes strongly bent. Early infected leaves smaller, pale green, margins ± spoon-like arched because of deflection downwards; cover dispersed on underside. Partial infestation usually does not induce galls. A. alpina, alpina subsp. caucasica: Hyaloperonospora arabidis-alpinae

15b Similar, but usually weaker malformations on stems and leaves. Arabis spp.: Peronospora arabidis-hirsutae

16a On inflorescences or flowers => 17

16b Siliques a little shortened and only slightly swollen. Ovaries containing yellowish to grey-violet spore masses. A. alpina, ciliata, hirsuta: Thecaphora thlaspeos

17a Malformations caused by animal inducers => 18

17b Malformations by fungi. Rachis of inflorescence stunted over large parts, ± swollen and bent, bearing many white-glossy bulges. Flowers conspicuously disfigured; calyx and corolla strongly enlarged; calyx leaves stunted or stronger developed and greened; anthers ± reduced, the filaments sometimes pillar-shaped swollen, greened. Arabis spp.: Albugo candida

18a Inflorescence largely or completely stunted. Flowers densely, bushy clustered, largely disfigured. Calyx and corolla, as well as stamens often irregularly swollen, elongated and greened; anthers hardly developed; ovaries ± puffed up (turgid), sometimes leafy transformations. A. hirsuta, parviflora: Lipaphis rossi

18b Terminal flowers of raceme clustered, all parts disfigured; organs greened, partially ± leafy, more densely pubescent. A. hirsuta: Aceria drabae

Gallers on Arabis glabra

1a Malformations on parts above ground => 3

1b Succulent galls on roots => 2

2a Malformations of very variable size, a few mm up to several cm, spindle-shaped to elongate-cylindrical, branched only exceptionally. Inside the nutritive cells are masses of minute, not conspicuously discoloured spores. “Clubroot”: Plasmodiophora brassicae

2b Almost similar, but lead-grey discoloured, sometimes on the side roots coralloid branched galls developing blackish spore balls: Urocystis coralloides

3a Localised or expanded malformations, usually on vegetative parts, caused by fungi which fruit at the gall surface => 5

3b Malformations caused by aphids which may encroach into the flowering shoots => 4

4a Usually only minor curl or folds on the leaf blades of several leaves, caused by mealy powdered aphids: Brevicoryne brassicae

4b Malformations very variable on usually many clustered leaves, at the end of main- and side shoots. Leaf blades deflected on all sides, ± curled. Infected inflorescence rachis severely stunted, densely crowded; some parts of older ones conspicuously enlarged, disfigured and greened: Lipaphis turritella

5a Plant diseased in often expanded parts. Young shoots with shortened and thickened internodes. Leaves pale green, leaf blade thickened, ± bladder-like, swollen and deflected at the margins. With extensive down of branched conidiophores on undersides. Infected rachis of inflorescence stunted to slightly swollen, bearing clustered, atrophied flower buds or flowers. Peronospora arabidis-glabrae

5b Leaf blades on underside with locally restricted, rotund, slightly swollen pads, at first white porcelain-like, then rupturing and with mealy dusting. Similar ± spindle-shaped bulges on leaf veins, stem parts and inflorescence rachis. Diseased flowers usually only with conspicuously enlarged, bulging calyx and ovaries. Corolla and stamens only sometimes enlarged and greened. Albugo candida

mod 20.iii.2020