Dichotomous table for gallers on Solanum

incl. Lycopersicon

by Hans Roskam

1a Malformations on higher situated parts above ground => 9

1b Variously shaped malformations on roots, stolons, tubers, root collar => 2

1c White, velvet cover on all parts of the plant, even underground. Attacked parts turn brown and wither. The conidia (in fact, sporangia) are ovoid or lemon-shaped, with an indistinct apical papilla. They are formed at the tip of seemingly undifferentiated hyphae, that here and there show irregular swellings. S. dulcamara, melongana, nigrum, physalifolium, tuberosum; also on Lycopersicon: Phytophthora infestans

2a Malformations only or mainly on roots => 7

2b Malformations on runners, tubers or on root collar, on other organs only under particular conditions and usually occurring simultaneously with previously reported malformations => 3

3a Malformations on stolons or tubers => 5

3b Malformations on root collar or on basally situated buds => 4

4a Gall formation not exclusively dependent on buds. Proliferations ± compact; rugose from outside, soon enclosed in tougher, corky tissue. Cavities inside many, running up to periphery. Inducer hardly microscopically detectable. Never on tubers and only exceptionally on stolons. “Bacterial-cancer|”. S. tuberosum: Agrobacterium tumefaciens

4b Proliferations usually close to ground; only developing from buds; soft at surface. Spores distinctly detectable in tissue. Galls very variable, depending on kind of host and developmental stage, time and degree of infestation; ± fissured, often coral-like; with strongly reduced primordia of organs. Pale below ground, above ground buds greened. Mainly on tubers, exceptionally on stolons or leaf parts; in potatoes never occurring on roots. “Potato-cancer”. S. tuberosum: Synchytrium endobioticum

5a Swellings usually less than 10 mm, flat; usually no connection with buds; on stolons or also on tubers => 6

5b Galls expanded, only developing from buds of tubers; at surface coral- or cauliflower-like, incised; at first white and compact, later on dark brown and rotting. On single or many buds, sometimes enveloping the complete tuber. “Potato-cancer”. On S. tuberosum and many tuber bearing relatives: Synchytrium endobioticum

6a The galls, about 3–6 mm long, rotund to oval, wart-like, mainly developing on tubers and on stolons, occasionally occurring mainly also on roots, at first white, later on dark-brown are ± rotund-oval, bladder-shaped and contain in the strongly hypertrophied nutritive cells of the swollen parenchyma masses of ball-like accumulated, rotund spores, made conspicuous by their dark colour. “Powder scab”. S. tuberosum as well as many, especially tuber bearing relatives: Spongospora subterranea

6b Developing tubers, almost only close to lenticels, with partially strongly arched swellings, also encroaching into the tissue, consisting of living cells, which contain many eelworms in between; weaker, mainly one-sided swellings sometimes simultaneously on stolons. S. tuberosum: Ditylenchus dipsaci

= Damage of tubers, known as “worm rot” has been caused by Ditylenchus destructor

7a Gall development inconspicuous from the outside, of irregular shape => 8

7b Roots with swellings usually on all sides, 2–5 mm long, slender spindle-shaped or ± conspicuous nodular, smooth-walled, sometimes joining, containing eelworms. S. dulcamara, melongena, nigrum, tuberosum, villosum: Meloidogyne spp.

7c Conspicuous, usually one-sided, sometimes fissured, almost cancer-like proliferations on thicker roots are caused by “Powder scab”: Spongospora subterranea

8a Roots externally not galled, or only on particular substrates, with slightly spindle-shaped galls. The temporarily about poppy-seed size, at first white, later on yellow, eventually brown, soon dropping cysts with giant cells developed inside roots. The healthy parts above the infestation site usually develop many “starvation roots”. On S. tuberosum and many wild potatoes, occasionally on S. dulcamara, luteum, melongena, also several forms of S. nigrum, etc.: Globodera rostochiensis

8b Roots with smaller, at first pale, later on brown galls, about 1–2.5 (4) mm long, wart-like, at surface often ± fissured, sometimes densely arranged or coalescing; similar infestation sometimes also on subterranean stem internodes. S. dulcamara, villosum, nigrum as well as several varieties and forms: Synchytrium endobioticum

9a Galls on stems, shoot tips or leaves => 11

9b Malformations on inflorescences or flowers => 10

10a Inflorescence largely stunted; flower primordia clustered into often long, ± raceme-like arranged galls. Flowers leafy in variously shaped, often densely haired rosettes. S. dulcamara: Aceria lycopersici

10b Flower buds strongly swollen, unopened. Galls greenish or ± violet tinged. Stamens and ovaries thickened and ± curved. Containing several ivory-white larvae. S. dulcamara: Contarinia solani

= Orange-yellow midge larvae of Macrolabis dulcamarae live as inquilines in galls on S. dulcamara

10c Berry disfigured and ± bumpy. Containing a single or several larvae. S. nigrum, tuberosum: Asphondylia trabuti

11a Malformations mainly on leaves or on shoot tips => 12

11b Gall development mainly on stems, occasionally over two or more internodes ± strongly shortened, curved, spongy, swollen and discoloured pale green. Leaves clustered at infestation site; development stunted; usually stalks, and midrib similarly galled; leaflets stunted and ± disfigured. Diseased parts usually prematurely withered. S. robustum, villosum, memphiticum, nigrum, tuberosum: Ditylenchus dipsaci

12a Expanded malformation of several organs on tips or terminally on shoots => 13

12b Leaf blade underside usually with many ± golden-yellow wart-like galls, less than 1 mm long. Also on petioles and basal stem parts; sometimes joined into ridges or crusts. S. dulcamara: Synchytrium aureum

13a Malformations caused by aphids => 15

13b Malformations caused by spittlebugs or mites => 14

14a All organs in often expanded arrangement terminally on apical or lateral shoots, and -buds ± stunted, bearing strongly reduced, often densely clustered, whitish or grey pubescent leaflets. Malformations sometimes up to 60 mm long and 40 mm wide; also encroaching into inflorescence. Lycopersicum esculentum; Solanum dulcamara, nigrum: Aceria lycopersici

14b Internodes close to shoot tip locally stunted and curved. Inserted leaves clustered, axial parts and margins curved; locally deep green. Similar malformations on larger leaves without involvement of axial parts. Lycopersicon esculentum, Solanum spp.: Philaenus spumarius

15a Aphids yellow or green => 17

= Many aphids, especially the host alternating species, inhabit not only potatoes, but also other hosts, during summer, preferably on leaves of varying age, which become variously disfigured. Aphids of some species may, in the later vegetative period, develop more luxuriously on plants already diseased by virus. It may be difficult to determine whether malformations are primarily the result of virus, making aphids secondary inhabitants, or primarily caused by aphids

15b Aphids almost black => 16

16a Leaves of ± stunted shoot tips clustered; ± deflected and curled over their top. Aphid only separable from the next species by microscopic characters, but preferentially colonising S. nigrum: Aphis fabae solanella

16b Similar malformations. S. nigrum, tuberosum: Aphis fabae fabae

17a Antennae longer than body => 18

17b Antennae of apterae not exceeding tip of abdomen, distinctly shorter than body => 19

18a Apterae pale yellowish to green, with a darker green spot at insertion of each siphunculus. Body pear-shaped, broadest at abdomen. 1.8–2.9 mm. Siphunculi pale, with darker tip, 1/5–1/4 body length, about twice as long as cauda. Alates green, with yellowish-brown to black-brown thorax, and with dark transverse stripes on abdomen. Lycopersicon esculentum, Solanum dulcamara, nigrum, tuberosum, villosum: Aulacorthum solani

18b Aphid green, often with a dark, green longitudinal stripe on back. Body spindle-shaped oval, glossy in adults, frosted in froth-covered nymphs. 2.5–3.6 mm. Siphunculi brownish, ¼–⅓ of body length, twice as long as cauda. Alates with pale brownish-yellow thorax, otherwise lacking pigmentation on back. Lycopersicon esculentum, Solanum dulcamara, melongena, nigrum, tuberosum: Macrosiphum euphorbiae

19a No tubercles on head. Siphunculi cylindrical or slightly conical. Abdomen of alates without dark median patch => 20

19b Head with tubercles at antennal bases. Apterae pale green, rarely reddish. Siphunculi pale, slightly club-shaped. Alates with head, thorax, a large median patch on abdomen, dark brown-black. Lycopersicon esculentum, Solanum dulcamara, melongena, pseudocapsicum, tuberosum: Myzus persicae

20a Apterae yellow to greenish-yellow. Siphunculi yellowish-green with brownish tips. S. dulcamara, melongena, tuberosum: Aphis nasturtii

20b Apterae dark-green spotted to dirty yellow. Siphunculi black, slightly conical. Lycopersicon esculentum; Solanum laxum, melongena, tuberosum: Species complex of Aphis gossypii

mod 30.iii.2020