Plant Parasites of Europe

leafminers, galls and fungi

gallers on Isatis

Dichotomous table for gallers on Isatis

by Hans Roskam

1a On parts above ground => 3

1b On roots => 2

1c Root collar with rotund, succulent, up to about 10 mm long swellings. Containing a single larva. I. tinctoria: Ceutorhynchus assimilis

2a Conspicuous, spindle-shaped to cylindrical swellings on main- and side roots. I. glauca, praecox, tinctoria: Plasmodiophora brassicae

2b Outside of roots little changed, temporarily bearing white to brown, poppy seed sized cysts. Giant cells develop inside. Isatis spp.: Heterodera schachtii

3a Malformations on shoot tips or on leaves, partially with conspicuous involvement of midrib; also on flowers => 7

3b Galls on shoot axis or petioles, without or with involvement of leaf blades => 4

4a Galls compact, caused by insects or fungi => 5

4b Galls pale green, spongy; confined to axial parts or only slightly encroaching into the leaf blade. I. tinctoria: Ditylenchus dipsaci

5a Rough-walled galls on stem, petiole or midrib, caused by beetle larvae => 6

5b Bulge-like, spindle-shaped, slight swellings on midrib, at first covered with glossy white, then mealy dusted sori. I. djurjudae, praecox, tinctoria: Albugo candida

5c The entire plant is disfigured. Upper side of the leaves locally bleached and galled; at the corresponding underside a greyish-white fungal bloom consisting of erect, distally strongly branched conidiophores. In the plant tissue locally oospores are formed, and particularly there galling occurs. I. tinctoria: Hyaloperonospora isatidis

6a Shoot axis stunted, with a long expanded swelling, containing several larvae. I. tinctoria: Ceutorhynchus sp.

6b Spindle-shaped, up to 12 mm long, also deep green inside gall; containing a single larva. I. praecox, tinctoria: Ceutorhynchus chalybaeus

7a Malformations on vegetative parts => 8

7b lower buds unopened, slightly swollen. Their peduncle slightly elongated and deflected, causing the galls to be ± hanging. Inside are several white to pale yellow midge larvae. Sometimes the larvae live in young flowering shoots in terminal, dense clusters of distinctly reduced buds between the organs. I. praecox, tinctoria: Contarinia nasturtii

8a Malformations of leaf blades => 10

8b Clustering of disfigured organs on ± stunted shoot tips => 9

9a Shoot axis distinctly shortened terminally, with dense tuft of ± stunted, almost sessile leaves, broadened at base, thickened and more pubescent. Containing several white to pale yellow larvae. I. praecox, tinctoria: Contarinia nasturtii

9b Shoot tips stunted, slightly thickened, organs inserted in dense clusters. Leaves stunted, curved and curled; flower buds reduced, partially ± exhibiting necrotic, greened organs. Infestation of isolated leaves results in the development of ± distinct, pale, ± reddish marbled swellings or folds. I. tinctoria, undulata: Brevicoryne brassicae

10a Leaf blade wrinkled and curled. I. tinctoria: Metaculus rapistri

10b On basal leaves the complete midrib is often ± curved, on larger leaves only the middle part over several cm is stunted and spongy, swollen, the leaf blades close to midrib are abnormally pubescent, bent upwards, strongly lacerated, on upper side bulge-like swollen. Containing several whitish to pale yellow larvae. I. praecox, tinctoria: Contarinia nasturtii

Last modified 22.iv.2020