Scutellonema bradys

 

Contents

 

Rev 11/19/2019

  Classification Hosts
Morphology and Anatomy Life Cycle
Return to Scutellonema Menu Economic Importance Damage
Distribution Management
Return to Hoplolaimidae Menu Feeding  References
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Classification:

        Tylenchina
        Tylenchoidea
         Hoplolaimidae
          Hoplolaiminae

Scutellonema bradys (Steiner & LeHew, 1933) Andrassy, 1958 

Yam Nematode

    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) Andrassy, 1958
      Scutellonema dioscorea Lordello, 1959

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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 (scutella) about 4 �m 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 �m long.

    Phasmids (scutella) usually just postanal.  . 

     


    Photomicrograph by Luma AlBanna

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

  Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:

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Distribution:

       South America and Africa (Nigeria).    

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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.

Scutellonema bradys is the most important plant parasitic nematode species  causing damage 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).

 

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Feeding:

All stages of the nematode are infective.

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Hosts:

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

For an extensive host range list for this species, click


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Life Cycle:

Ecophysiological Parameters:

For Ecophysiological Parameters for this species, click If species level data are not available, click for genus level parameters

 

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.


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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 spp.) (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 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., D. cayenensis Lam., D. alata L. and D. dumetorum (Kunth) Pax., are all susceptible to S. bradys infection.

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Management:

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 soil fumigant.

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).

 Resistance

Host Plant Resistance, Non-hosts and Crop Rotation alternatives:

For plants reported to have some level of resistance to this species, click

 

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References:

CIH Descriptions of Plant-parasitic Nematodes, Set 1, No. 10 (1972)

Bridge, J. 1972. Nematode problems with yams (Dioscorea spp.) in Nigeria. PANS 18:89-91.

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

 

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Copyright © 1999 by Howard Ferris.
Revised: November 19, 2019.