Scutellonema bradys

    Synonyms:
      Hoplolaimus bradys Steiner & LeHew, 1933
      Anguillulina bradys (Steiner & LeHew, 1933) Goodey, 1935
      Rotylenchus bradys (Steiner & LeHew, 1933) Filipjev, 1936
      Rotylenchus blaberus Steiner, 1937
      Scutellonema blaberum (Steiner, 1937) Andrássy, 1958
      Scutellonema dioscorea Lordello, 1959

Morphology and Anatomy:

Female:

Body straight to slightly arcuate when relaxed, 0.88-1.11 mm
annules about 1.6 µm wide near middle of body
lateral fields about one-fifth body-width, with 4 incisures, areolated at phasmids and anteriorly, sometimes irregularly areolated on midbody and tail.
Lip region knob-like, offset by a constriction, with a labial disc and 6 to 8 (usually 7) annules lacking longitudinal striations. Cephalic sclerotization strong.

Photomicrograph by Luma AlBanna

Female:

Stylet well developed with large oval to rounded basal knobs bearing flattened, indented or irregular anterior surfaces; anterior tapering portion a little less than half spear length.
Hemizonid usually distinct, 2-3 annules long, 0-3 annules anterior to excretory pore and close to esophago-intestinal junction. Hemizonion 1 annule long, about 8 annules behind the excretory pore.
Esophageal glands elongate, overlapping intestine dorsally and dorso-laterally; nucleus of dorsal gland anterior to those of subventrals.
Ovaries paired, with oocytes in 1 to 2 rows. Spermathecae rounded, sometimes oval, usually packed with sperms. Vulva a transverse slit with conspicuous cuticular thickenings towards ends (? ="vaginal glands" of Sher, 1964). Epiptygma inconspicuous.
Intestine partially overlapping rectum.

Tail variable, with obtusely rounded striated terminus and 13 to 20 annules.

Photomicrograph by Luma AlBanna

Phasmids about 4 µm in diameter, with pore-like aperture, at or up to 6 annules anterior to anus.

Photomicrograph by Luma AlBanna

Male:

Abundant. Similar to female except for sexual dimorphism, 0.85-1.0 mm.
Testis outstretched; spermagonia in 3-4 rows; sperms about 4 µm in diameter
Bursa large, crenate, enclosing tail.
Spicules slightly cephalated and ventrally arcuate, with large distal flanges.

Capitulum (=telamon) prominent, about 10 µm long.

Phasmids usually just postanal.

Photomicrograph by Luma AlBanna

Cuticular, non-protoplasmic terminal portion of tail 11-16 µm long.

Distribution:

Economic Importance:

Endoparasite in yam roots and tubers. Enters tubers through growing point and cracks. Continues to feed and multiply while tubers are in storage, resulting in rot.

Feeding:

Hosts:

Pest of yam (Dioscorea spp.), corn, cotton, cowpea, banana, coconut palm, and others.

Life Cycle:

Luc & Hoestra (1960) encountered only a few individuals in the yam roots and tubers, around which a larger population was present, suggesting that the greater part of the life cycle of the nematode must take place in the soil.

Life cycle appears simple. Eggs are laid in soil or plant tissues (roots and tubers) where they hatch, and the juveniles develop into adults by subsequent molting.

Damage:

Yams (Dioscorea spp.) are annual or perennial climbing plants with edible underground tubers. More than 95% of the world's yams are currently grown in sub-Saharan Africa, with the remainder grown in the West Indies and parts of Asia and South and Central America. Yam is a preferred staple food crop in West Africa.

Yams are affected insects, nematodes, fungal and bacterial diseases, and viruses, which either single or in combination are responsible for suboptimal yields and deterioration of the tuber in storage. The major nematodes pests yam nematode (Scutellonema bradys), root-knot nematode (Meloidogyne incognita), and lesion nematode (Pratylenchus sp.) (IITA).

Scutellonema bradys reproduces and builds up large populations in stored yam tubers and causes severe damage during storage. The maximum population recorded was 6,200 nematodes/g of tuber.

Damage caused by nematodes makes tubers more prone to fungal and bacterial attacks, e.g., dry rot and wet rot.

Management:

Leave soil fallow for several months; use healthy seed tubers; dip all propagating material in hot water (50 C for 30 min);

Screening of 220 accessions of Dioscorea rotundata (yam) revealed variation in susceptibility to the yam nematode (Scutellonema bradys) and the root knot nematode (Meloidogyne incognita). Two accessions of D. dumetorum (from Ghana and Cameroon) were highly resistant to S. bradys (IITA annual report,