Dichotomous table for gallers on Sisymbrium

(incl. Murbeckiella)

by Hans Roskam

1a On parts above ground => 5

1b On roots or root collar => 2

2a Galls on roots => 3

2b Whitish, rotund, one-chambered swellings on root collar, up to about 6 mm long. sometimes with several and ± coalescing. Each chamber containing a single white larva. S. altissimum, austriacum, loeselii, officinale: Ceutorhynchus assimilis

3a Galls conspicuous, of very variable size, usually much larger than 5 mm => 4

3b Swellings nodular, or slender spindle-shaped, up to about 5 mm long and 3 mm broad. S. altissimum: Meloidogyne hapla

= The cyst forming eelworms Heterodera cruciferae and H. schachtii have also been recorded.

4a Galls on thinner roots slender-spindle-shaped, on thicker roots acuminated, oblong-oval to cylindrical; succulent. With masses of minute spores inside cells. “Clubroot”. Sisymbrium spp.: Plasmodiophora brassicae

4b Main- or lateral roots with ± pronounced, also twisted, many-chambered swelling. S. officinale, etc.: ? snout beetle

5a Malformation is limited to a single organ or its parts => 11

5b Malformations include the complete plant or large parts, including buds, and terminal or lateral vegetative or generative shoot => 6

6a Malformations caused by aphids, spittlebugs or fungi => 9

6b Malformations caused by larvae of gall midges => 7

7a Gall lacking conspicuous pubescence => 8

7b Large part of axis of plant stunted. Main- and side shoots severely stunted. Leaves reduced, clustered, ± depressed, together with disfigured flowers, transformed into a strongly pubescent, dense tuft-like gall. Containing many ivory-coloured larvae. S. altissimum, austriacum, loeselii, orientale: Dasineura bayeri

8a Organs densely clustered terminally on shoots or in leaf axils; swollen at base and transformed into a fleshy gall, which variously is overtopped by ± severely stunted to healthy organs. Leaves thickened and pale, especially at base. Infected flower buds turgid, ± unopened, with thickened, sometimes adnate stalks and swollen corolla and stamens. Already present siliques basally, like their stalks, swollen, ± stunted and distorted. Larvae white to pale yellow, jumping. Sisymbrium spp.: Contarinia nasturtii

8b Galls mostly similar, almost as variable as the previous species. Larvae white or yellow, non-jumping. S. irio, officinale, orientale, volgense: Dasineura sisymbrii

9a Malformations caused by animals => 10

9b Lateral shoots stunted, thickened, ± curved; often growing in opposite directions. The inserted organs stunted and disfigured. All parts soon covered with white down of branched conidiophores. S. altissimum, irio, loeselii, luteum, officinale, volgense: Hyaloperonospora sisymbrii-loeselii

10a Whole plant mostly stunted, compact and variously disfigured. Leaves ± curved, spoon-like, curled, often paler green, violet-tinged. Flower buds or flowers clustered, disfigured; similarly discoloured. S. altissimum, loeselii, officinale: Lipaphis erysimi

= Apparently the mealy cabbage aphid Brevicoryne brassicae occurs temporarily and sparsely on Sisymbrium. Galls induced by this species are not definitely known.

10b Young shoot axial parts locally stunted and slightly bent; the ± clustered leaves deflected, leaf blades curved and curled. Similar stunting and occasionally clusters of disfigured young inflorescences bearing flowers as well as fruits. Sisymbrium spp.: Philaenus spumarius

11a Galls on inflorescences or flowers => 21

11b Stem- or leaf galls => 12

12a On leaves => 17

12b On stems => 13

13a The inducers or their fructifications occur on the outside of galls => 15

13b Larvae inside galls => 14

14a Younger stems with spindle-shaped swelling, up to 20 mm long and about 4 mm thick. Containing a single beetle larva inside the green tissue. S. altissimum, officinale, orientale: Ceutorhynchus chalybaeus

14b Stem irregularly swollen over several cm length, often bent and ± stunted. The increased pith containing several beetle larvae. S. altissimum, officinale: Ceutorhynchus napi

15a Swelling covered with white fruiting bodies => 16

15b Irregular bulging swellings, which bear several small rimmed depressions. S. altissimum: Planchonia arabidis

16a Localised to expanded, one- or all-sided, ± curved swellings on stems of vegetative or flowering shoot. Inserted leaves stunted, bent over their length, pale green, thickened and brittle, inserted flowers ± atrophied in all their parts. Down loose, conidiophores branched. Sisymbrium spp.: Hyaloperonospora sisymbrii-loeselii

16b Similar, usually more conspicuous malformations with sori of variable size, spindle-shaped, at first glossy white, porcelain-like, later on ruptured and dusty. If on inflorescences, causing conspicuous malformation of flowers. Sisymbrium spp.: Albugo candida

17a Pad-, spindle- or bladder-shaped swellings caused by fungi => 20

17b Malformations caused by animals => 18

18a Galls on petioles or leaf veins => 19

18b Leaf tip rolled upwards at margin, irregularly thickened, abnormally haired. S. altissimum, loeselii. officinale, orientale: Aceria drabae

19a Spindle-shaped or acuminate oblong-oval swellings on petiole or midrib, about 10–15 mm long, ± flattened, also deep green inside. Containing a single beetle larva. S. altissimum, officinale, orientale: Ceutorhynchus chalybaeus

19b Leaf blade folded together to varied extent over the locally thickened midrib, at the base of the infestation swollen, pouch-like, ± discoloured; containing several white to pale yellow, jumping larvae. Sisymbrium spp.: Contarinia nasturtii

19c Small gall terminally on young plant, consisting of 4 or 5 disfigured leaves, succulent, pubescent. Containing several reddish larvae. Murbeckiella zanonii: Dasineura sisymbrii

20a White, at first glossy, porcelain-like, then rupturing and with white dusting, leaf blade rotund on underside, on veins and petioles forming ± spindle-shaped pads. Leaf blades of S. officinale deep violet-red close to the often ± discoloured sori. Albugo candida

20b Leaf blades locally slightly swollen and discoloured; completely infected leaves stunted, pale green, deflected at margin and venation especially distinctly thickened. On underside with white down of branched conidiophores. Sisymbrium spp.: Hyaloperonospora sisymbrii-loeselii

= Very similar is Peronospora sisymbrii-orientalis on S. orientale, which may facultatively induce similar gall-like malformations on its host.

21a Flower galls, usually at same time with malformations of inflorescence stalk => 22

21b Single flower swollen, unopened. Larvae white, non-jumping. S. altissimum: Gephyraulus raphanistri

21c Silique swollen, containing white midge larvae. S. loeselii: Dasineura rostratae

22a Flower buds or flowers disfigured, clustered at the tip of panicles => 23

22b Axial parts slightly changed or locally swollen, bearing single or several severely disfigured flowers. Calyx leaves hypertrophied, corolla leaves transformed into elongated green tongues, stamens ± leafy; ovary developing into an elongated, sometimes bent tube; on all parts often several ± rotund-oval, white sori of fungus. S. altissimum, officinale: Albugo candida

23a Several swollen and unopened flower buds in loose or dense sequences at the tip of ± stunted and swollen, terminal- or axillary racemes. Larvae white to pale yellow, jumping. Sisymbrium spp.: Contarinia nasturtii

23b Similar gall, contain non-jumping larvae. Sisymbrium spp.: Dasineura sisymbrii

23c Axis shortened; ± greened or leafy, bearing abnormally pubescent flowers. S. altissimum, loeselii. officinale, orientale: Aceria drabae

mod 5.iii.2020