Dichotomous table for gallers on Beta

by Hans Roskam

1a On parts above ground of young plants or on leaves => 8

1b On roots or on beet => 2

= The occurrence of Rhodococcus fascians has been recorded on sugar beet. This bacterium causes the formation of “leafy galls”.

2a On beet => 4

2b On side roots => 3

3a Roots often with many nodular, barrel- or spindle-shaped swellings, usually not exceeding 3–4 mm long, sometimes joining and usually developing side roots. Causer inside gall. B. vulgaris: Meloidogyne hapla

3b All parts of plant severely disfigured. Development of roots stunted, their tips pale yellowish-white, thickened and ± crooked. B. vulgaris: Paralongidorus maximus

3c Similar swellings on root tips. B. vulgaris: Pratylenchus pratensis

3d Roots from the outside not or only slightly swollen; inside with giant cells. Females rupturing from rind, temporarily attached to the root with whitish, later on brown, about poppy seed-size, lemon-shaped egg capsules. Beet corpus usually remaining thin, often densely covered with side roots, so called “hunger roots”. Plant disfigured. B. vulgaris: Heterodera schachtii

4a Root body with ± conspicuous proliferations => 5

4b Young beet gall-like thickened, usually densely provided with adventitious roots. Contains a single larva. B. vulgaris: Bothynoderes affinis

5a Proliferations only rarely exceeding 10 mm => 7

5b Swellings in full-grown condition at least partially much larger than 10 mm => 6

6a Proliferations succulent, with uniform tissue, laterally attached to the upper part of the beet, of variable size ranging from hazelnut to child head; surface glabrous, rarely partitioned into smaller, 4–10 mm thick, usually rotund, deep compartmented single protuberances. Older galls ± browned. B. vulgaris: Agrobacterium tumefaciens

6b Smaller or more expanded, bean-, rarely also fist-sized proliferations, sometimes basally ± constricted, cancer-like, with cavities inside. At first ± orange-coloured, later on browned and with cracked surface. Usually on upper part of beet, sometimes apically elongated. “Beet cancer”. On B. vulgaris: Physoderma leproides

7a Upper part of sometimes many-headed beet body with scab- to cancer-like, cracked parts, which show ± concentric rings in cross-section; skin often detached; underlying tissue spongy, swollen, contains eelworms. B. vulgaris: Ditylenchus dipsaci

= In many aspects a similar, very variable infestation pattern is caused by the proteobacterium Actinomyces scabies; the proliferations usually develop in girdle-shaped arrangements of parasite-free, soon browned, dead, uniform cell complexes which are not true galls. The apically neighbouring area is often depressed and locally replenished with scabby remains of tissue.

7b Up to 10 mm high and about 10–30 mm broad, cracked surface, single or sometimes joined into groups mainly on upper beet part. B. vulgaris: Xanthomonas beticola

8a On larger leaves without distinct involvement of venation => 9

8b Axial parts of shoot, as well as stalks, midrib and lower parts of ± stunted juvenile- or rosette leaves stunted and spongy, swollen. Galls very variable in position and size, pale green, ± wrinkled on surface. B. vulgaris: Ditylenchus dipsaci

9a Malformations caused by fungi which fruit at surface => 14

9b Malformations caused by animals or fungi which fruit inside the gall => 10

10a Leaf blade curled or rolled by animal causers => 11

10b Leaves of young plants, especially basal part of leaf blade, often with many rotund or oblong glabrous galls, pad- or bulge-like, at surface. Leaf blades often stunted, narrowed, pale green, also the margins ± curled. Galls soon decaying. B. vulgaris: Physoderma leproides

11a Leaf blade curls caused by aphids, plant bugs or thrips => 12

11b Leaf blade usually obliquely folded downwards, also over the tip, ± nest-like or with strong, loose rolling. Strongly curled and deep green close to the froth-covered nymph on the underside. B. vulgaris: Philaenus spumarius

12a Malformations caused by aphids => 13

12b Petiole and leaf venation curved upwards, thickened and brittle; leaf blades strongly curled; inner rosette leaves if strongly infected often ± clustered-like head of lettuce. Caused by the virus Savoia betae and transmitted by the bug Parapiesma quadratum

13a Aphids black; often in large colonies on leaf underside. Leaf blades of basal- or stem leaves bent downwards and curled to a great extent. B. vulgaris: Aphis fabae

13b Aphid green. Leaf blade primarily slightly curled. B. vulgaris: Myzus persicae

14a Young leaves stunted, often shorter stalked; several in centre of rosette diseased, ± fleshy thickened, brittle; leaf margin rolled downwards and strongly curled, on underside soon covered with a woolly, dirty violet down of forked conidiophores. B. vulgaris: Peronospora farinosa

14b Leaf blades with rotund, slightly depressed yellowish pads on upper side, bulging on underside, bearing pale yellow aecia on underside, and honey-yellow spermogonia on upper side. Sori on veins or stalks often oblong spindle-shaped. B. vulgaris: Uromyces beticola

14c On various above ground, ± swollen parts of Beta species may occur the often densely grouped, whitish spermogonia and aecia of Puccinia isiacae

mod 20.iii.2020