Dichotomous table for gallers on Braasica

by Hans Roskam

1a On inflorescences, flowers or fruits => 23

1b On vegetative parts => 2

2a On parts above ground => 6

2b On root collar or on roots => 3

3a On roots => 4

3b Root collar with ± rotund, succulent swellings, about 8–10 mm long, containing a single larva. Galls, especially on perennial species, often many per plant and largely coalesced into ± lumpy gall complexes; sometimes also on the basal stem parts or close to surface on main root, especially on cabbage. B. napus, oleracea: Ceutorhynchus assimilis

= The snout beetles Aulacobaris coerulescens and Melanobaris laticollis have erroneously been reported as inducers of root collar-, root- and stem galls. The larvae develop by boring into ungalled roots or above ground stem parts and occasionally arrive in galls already produced by other inducers

4a Nodule-shaped swellings, only a few mm long, on the finer side roots, not noticeably swollen, transiently bearing cysts => 5

4b Main- or side roots often with very conspicuous, often clustered, spindle- or ± finger- to nodule-shaped, thick succulent, massive swellings; inside many cells with dense masses of minute spores. B. oleracea: Plasmodiophora brassicae

= Occasionally conspicuous nodular proliferations occur on main roots, or more frequently on above-ground parts, especially on forms of B. rapa. The tissue is, in contrast to that caused by Plasmodiophora brassicae, uniform coloured and without development of spores. Cause unknown, but some authors attributed these malformations to Agrobacterium tumefaciens

5a Roots with spindle-shaped or rotund, smaller, sometimes about pea- to exceptionally nut-size swellings caused by eelworms living inside. B. napus, oleracea, rapa, incl. subspecies and forms. Meloidogyne hapla

5b Inconspicuous, some side roots bearing root galls. B. napus, oleracea: Meloidogyne artiellia

5c Roots externally not swollen; inside with giant cells. Occasionally stronger development of side roots. Temporarily at surface with about poppy-seed sized, lemon-shaped, at first milk white, then browned cysts. Brassica spp.: Heterodera schachtii

5d On many cabbage species occur also the very similar, but slightly smaller, on average up to 0.6 mm, and more rotund cysts of Heterodera cruciferae

6a Malformations with white sori on surface => 22

6b Malformations caused by animal parasites => 7

7a Terminally on main- and side shoots => 18

7b On stems or leaves => 8

8a On stalks or leaf blades of leaves => 10

8b Stem with short spindle-shaped or elongate expanded swellings => 9

9a Thin stems with all-sided, thicker stems with one-sided, spindle-shaped swellings, 10–15 mm long, glabrous, also green inside. Contains a single larva. B. napus, nigra, oleracea, rapa: Ceutorhynchus chalybaeus

= Aulacobaris coerulescens, A. cuprirostris, A. lepidii, A. chlorizans have been reported as causers of stem galls. The larvae tunnel in the stem and the thicker roots; pupation in the gallery

9b Development of stem, especially of winter oil seed, stunted in spring, swollen over variable length, often ± s-shaped curved, often erupting over large expansion. In the strongly enlarged pith many, up to 7 mm long, yellowish-white apodous larvae with brownish, relatively large head capsule. B. napus, oleracea, rapa: Ceutorhynchus napi

= Occasionally has, especially for Brassica, been recorded Ceutorhynchus pallidactylus. Oviposition is not followed by gall formation. For B. rapa thickened leaf parenchyma has been reported caused by Ceutorhynchus leprieuri

10a Malformations mainly of leaf blades => 12

10b Galls on petioles or main venation => 11

11a Galls 10–15 mm long, compact, spindle-shaped, with glabrous surface, also green inside. B. napus, nigra, oleracea, rapa: Ceutorhynchus chalybaeus

11b Stems of germinating, also older plants or petioles, usually also the basal part of midrib shortened, spongy, swollen, yellowish green; at infestation sites brittle and necrotic, at surface ± undulately-wrinkled, variously on leaf blades, also encroaching on parts of rape. B. napus: Ditylenchus dipsaci

12a Leaf blade ± curled, loosely rolled inwards or folded => 14

12b Leaf blade with very narrow marginal roll or with lenticular galls => 13

13a Galls occurring from autumn to early spring; lenticular, up to 5 mm across, succulent, on both sides flat protruding, also green inside, especially conspicuous on yellowing parts, often many per leaf, often including main veins. Containing a single larva. B. rapa, rarely B. napus, oleracea: Ceutorhynchus leprieuri

13b Leaf blade with narrow marginal roll upwards. B. nigra: Inducer unknown

14a Malformations caused by aphids or spittlebugs => 15

14b Leaf blades to varied extent swollen and stunted, bent upwards along midrib; pale green; several whitish to pale yellow, jumping midge larvae on upper side between folds. B. napus, oleracea, rapa, souliei subsp. amplexicaulis: Contarinia nasturtii

15a Malformations caused by aphids => 16

15b Leaf blades of larger leaves deflected into mainly oblique rolls or distortions; usually curled and deep green close to froth covered froth-covered nymph. Brassica spp.: Philaenus spumarius

16a Aphid green => 17

16b Aphid black. Leaf blade at margin ± deflected, curled, infestation mainly on terminal stem leaves. Brassica spp.: ? Unidentified aphid

= Black aphids of Aphis fabae s.l. do not cause galls on Brassica. However, they may occur as inquilines in galls caused by other inducers

17a Leaf blade with expanded, conspicuously bulge- or bladder-like, pale green, on many species sometimes reddish or violet marbled folds or swellings; large colonies of densely grey-powdered aphids often on underside. B. napus, oleracea, rapa: Brevicoryne brassicae

17b Aphid not mealy powdered. Leaf blades of stem leaves often rolled downwards at margin, ± curled. B. napus, oleracea: Myzus persicae

18a Galls on tips of rosette leaves => 19

18b Tips of flowering main- and side shoots severely stunted; leaves as well as flower buds densely clustered, variously swollen at base. Similar malformations also on axillary, often hardly developed shoots. Between the galled parts are several whitish- to pale yellow, jumping larvae. B. napus, oleracea, rapa, souliei subsp. amplexicaulis: Contarinia nasturtii

19a Inducers live inside malformations => 20

19b Central leaves disfigured. Lower parts of petiole, vegetative point, especially at infected area, strongly swollen and bent sidewards. Between galled parts are several whitish- to pale yellow, jumping larvae. B. napus, oleracea, rapa, souliei subsp. amplexicaulis: Contarinia nasturtii

20a Shoot thickened over variable length, stunted. Leaves ± clustered, the inner ones often severely stunted or dead. Pith often contains several beetle larvae => 21

20b Stem of young plants completely or partially spongy, pale green; infestation similarly encroaching into petioles and leaf veins, mainly on underside. Galls contain many eelworms. B. napus: Ditylenchus dipsaci

21a Shoots, occasionally also leaf base of non-shooting forms, distinctly thickened; pith greatly increased. Vegetative point often largely stunted or necrotic. Several beetle larvae in heavily infected pith. B. napus, oleracea, rapa: Ceutorhynchus napi

21b Similar, usually weaker swellings inhabited by only 1 to 3 larvae. B. oleracea and forms. Ceutorrhynchus rapae

22a Loose down of branched conidiophores in ± expanded sori on the underside of only pale leaves. Rarely on leaf veins or young stems causing occasionally minor swellings, usually containing oospores. B. napus, nigra, oleracea, rapa: Hyaloperonospora brassicae

22b Sori on leaf underside rotund, on stem parts oblong-oval to spindle-shaped, compact, at first closed, glossy, porcelain-like, with mealy dusting after rupturing. Often many per plant; hardly cecidogenic on the leaf blades, on young stems often developing distinct pads. B. juncea, napus, nigra, oleracea, rapa: Albugo candida

22c Leaf with small hard, solid, gregarious pustules caused by fungus, less than 0.5 mm across. Brassica spp.: Synchytrium aureum

23a Malformations on single or many flowers or fruits; stem parts hardly disfigured => 26

23b Inflorescence disfigured => 24

24a Malformations caused by aphids or spittlebugs => 25

24b Racemes greatly shortened terminally; flower buds densely clustered, severely stunted, occasionally swollen at base. Between buds are several whitish- to pale yellow, jumping larvae. B. oleracea, rapa, souliei subsp. amplexicaulis: Contarinia nasturtii

25a Midrib locally swollen and severely stunted, usually bent to one side; flowers clustered, variously disfigured. Leaves distorted and curled. Containing a froth-covered nymph. Brassica spp.: Philaenus spumarius

25b Inflorescence broom-like disfigured and bent, longitudinal growth stunted. Flowers often mostly necrotic; occasionally also several largely disfigured shoots. Stems at first bearing ± densely grey powdered aphids. B. napus, oleracea, rapa: Brevicoryne brassicae

26a Malformations of ovaries or fruits => 29

26b Malformations of flowers => 27

27a Single or several buds of inflorescence swollen, unopened => 28

27b Usually consecutive flowers of large parts of inflorescence, often terminally of raceme variously disfigured; especially the ovaries prematurely elongated and increasing towards the top, swollen like enlarged, slender Capsella siliques; stamens and corolla disfigured, greened and often, like calyx necrotic. B. napus, oleracea and forms. Cause unknown – ? virus disease

28a Gall ± globular; calyx enlarged; corolla shortened; stamens disfigured, their filaments swollen and bent; anthers aborted; ovaries stunted, swollen; style and stigma necrotic. Containing several white, later on pale yellow, jumping larvae. B. oleracea, rapa, souliei subsp. amplexicaulis: Contarinia nasturtii

28b Similar flower galls with several, but non-jumping, larvae which are also white when mature. B. barrelieri, napus, oleracea, rapa: Gephyraulus raphanistri

29a Young or often well-developed shoots ± shortened and slightly swollen over their complete length, or with ± expanded often pale green swellings causing conspicuous curving. Galled siliques sterile or ± early bursting => 30

29b Ovaries, sometimes also calyx leaves and stamens, conspicuously disfigured, enlarged, with white at first closed, soon dusty sori. B. juncea, napus, nigra, oleracea, rapa: Albugo candida

30a Larvae white, only rarely pale yellow later on, non-jumping, usually many per silique. B. napus, oleracea, rapa: Dasineura napi

= Fruit galls, occasionally recorded from literature for Ceutorhynchus assimilis or for larvae of unidentified snout beetle, might also be attributed to this midge

30b Silique swollen, contains a single orange midge larva. B. nigra: Asphondylia stefanii

mod 23.xii.2019