Scutellonema bradys (Steiner & LeHew, 1933) Andrassy, 1958
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) Andrassy, 1958
Scutellonema dioscorea Lordello, 1959
Body straight to slightly arcuate when relaxed, 0.88-1.11 mm
annules about 1.6 Âµm wide near middle
lateral fields about one-fifth body-width, with 4 incisures,
areolated at phasmids and anteriorly, sometimes irregularly areolated on midbody and tail.
Photomicrograph by Luma AlBanna
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.
Abundant. Similar to female except for sexual dimorphism, 0.85-1.0 mm.
Testis outstretched; spermagonia
in 3-4 rows; sperms about 4 Âµm in diameter
Bursa large, crenate, enclosing tail.
Spicules slightly cephalated and ventrally arcuate, with large distal flanges.
Capitulum (=telamon) prominent, about 10 ï¿½m long.
(scutella) usually just postanal.
Cuticular, non-protoplasmic terminal portion of tail 11-16 ï¿½m long.
Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:
South America and Africa (Nigeria).
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.
Scutellonema bradys is the most important plant parasitic nematode species
to yams (Dioscorea spp.). The nematode feeds as a migratory
endoparasite on the peridermal and sub-peridermal cellular
layers of the tuber causing destruction of the cells and browning of cell
walls. The feeding reults in a characteristic dark-brown layer
extending 1-2 cm into the tuber which becomes a dry rot disease of the
tubers. The dry rot causes a persistent decline of tuber quality and
even total loss during storage of tubers (Bridge et al., 2005). The lesions
progress from yellow to brown and black. The epidermis of the tuber
may remain intact or it may develop cracks which faciliate invasion of fungi
an bacteria and lead to a wet rot (Bridge, 1972; Bridge et al., 2005,
Kolombia et al., 2017).
All stages of the nematode are infective.
Pest of yam (Dioscorea spp.), corn, cotton, cowpea, banana, coconut palm, and others.
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.
Scutellonema. bradys survives and reproduces in stored tubers
throughout the dry season and can cause severe damage during storage,
reducing the size and marketable value of the yams. In a sampling of
yam tubers from seven town markets in Nigeria, 43% were infected with S.
bradys, with population levels as high as 6,200 nematodes per g of tuber.
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
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 ranges from small brown or yellow lesions
to extensive rotting throughout the outer layers of
the tuber, depending on the nematode population
densities. The yam nematodes can cause reduction in
tuber size by destructive feeding on the root and
tuber tissues of maturing yams in the soil. They
invade the primary roots growing from the
rhizomatous head of the tuber and can enter the
young tubers early in their development by way of
the tuber growing point, along side emerging roots
and shoots, and through the roots. Invasion of the
tuber can also occur through cracks in the
epidermis. The damage predisposes tubers to fungal
and bacterial pathogens, resulting in dry and wet
rots commonly found in stored tubers (Bridge, 1972;
Bridge et al., 2005; Kolombia et al., 2017).
The four main yam species grown in Nigeria, Dioscorea rotundata Poir.,
cayenensis Lam., D. alata L. and D. dumetorum (Kunth) Pax., are all
susceptible to S. bradys infection.
Leave soil fallow for several months; use healthy seed tubers; dip all propagating material in hot water (50 C for 30 min);
D-D was an effective
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),
Scutellonema bradys is disseminatedbin infected seed tubers.
Also, nematodes may survive in the soil on other hosts.
Crop rotation is complicated by the inter-cropping practices employed by
many farmers in Nigeria.
Eradication of nematodes in infected seed tubers is a management goal.
Hot water treatment at
50C for 30-40 minutes is reported to be effective (Bridge, 1972).
Host Plant Resistance, Non-hosts
CIH Descriptions of Plant-parasitic Nematodes, Set 1, No. 10 (1972)
Bridge, J. 1972. Nematode problems with yams (Dioscorea spp.) in Nigeria.
Bridge, J., Coyne, D.L. & Kwoseh, C.K. (2005). Nematode parasites of
tropical root and tuber crops (excluding potatoes). In: Luc, M., Sikora,
R.A. & Bridge, J. (Eds). Plant parasitic nematodes in subtropical and
tropical agriculture, 2nd edition. Wallingford, UK, CAB International, pp.
221-258. DOI: 10.1079/9780851997278.0000
Kolombia, Y.A., G. Karssen, N. Viaene, P. L. Kumar, L . Joos, D. L. Coyne
and W. Bert. 2017. Morphological and molecular characterisation of Scutellonema species
from yam (Dioscorea spp.)
and a key to the species of the genus. Nematology 19: 751-787