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Plantwise Technical Factsheet

common spiral nematode (Helicotylenchus dihystera)

Host plants / species affected
Abelmoschus esculentus (okra)
Acalypha hispida (Copperleaf)
Actinidia deliciosa (kiwifruit)
Aechmea fasciata
Agrostis capillaris (common bent)
Allium cepa (onion)
Allium chinense (spring onion)
Allium schoenoprasum (chives)
Anacardium occidentale (cashew nut)
Ananas comosus (pineapple)
Andropogon pseudapricus
Annona muricata (soursop)
Apium graveolens (celery)
Arachis hypogaea (groundnut)
Araucaria
Araucaria cunninghamii (colonial pine)
Artocarpus altilis (breadfruit)
Avena sativa (oats)
Begonia
Beta vulgaris (beetroot)
Brachiaria brizantha
Brassica
Broussonetia papyrifera (paper mulberry)
Buxus sempervirens (common boxwood)
Cajanus cajan (pigeon pea)
Calopogonium
Camellia sinensis (tea)
Canna indica (canna lilly)
Capsicum annuum (bell pepper)
Carica
Carica papaya (pawpaw)
Cassia alata (Ringworm senna)
Casuarina (beefwood)
Ceiba pentandra (kapok)
Cenchrus ciliaris (Buffel grass)
Cenchrus echinatus (southern sandbur)
Centrosema pubescens (Centro)
Chamaecyparis (false cypress)
Chloris gayana (rhodes grass)
Cinnamomum verum (cinnamon)
Citrullus lanatus (watermelon)
Citrus aurantiifolia (lime)
Citrus jambhiri (rough lemon)
Citrus limon (lemon)
Citrus sinensis (navel orange)
Citrus x paradisi (grapefruit)
Cocos nucifera (coconut)
Coffea (coffee)
Coffea arabica (arabica coffee)
Colocasia esculenta (taro)
Crossandra undulifolia
Crotalaria juncea (sunn hemp)
Crotalaria spectabilis (showy rattlepod)
Cryptanthus bromelioides
Ctenanthe oppenheimiana
Cucumis sativus (cucumber)
Cucurbita moschata (pumpkin)
Cucurbita pepo (marrow)
Cymbidium
Cynodon dactylon (Bermuda grass)
Datura (thorn-apple)
Daucus carota (carrot)
Delonix regia (flamboyant)
Desmodium tortuosum (Florida beggarweed)
Digitaria (crabgrass)
Dioscorea (yam)
Dioscorea alata (white yam)
Elaeis guineensis (African oil palm)
Eleusine coracana (finger millet)
Eriobotrya japonica (loquat)
Eucalyptus
Eucalyptus deanei
Eustoma grandiflorum (Lisianthus (cut flower crop))
Falcataria moluccana (batai wood)
Ficus benjamina (weeping fig)
Ficus elastica (rubber plant)
Fortunella x crassifolia (meiwa kumquat)
Fragaria ananassa (strawberry)
Fragaria vesca (wild strawberry)
Gardenia
Glycine max (soyabean)
Gossypium hirsutum (Bourbon cotton)
Helianthus annuus (sunflower)
Hevea brasiliensis (rubber)
Hibiscus (rosemallows)
Hordeum vulgare (barley)
Humulus lupulus (hop)
Ilex cornuta (Chinese holly)
Ilex crenata (Japanese holly)
Impatiens (balsam)
Indigofera hirsuta (hairy indigo)
Ipomoea batatas (sweet potato)
Ipomoea brasiliensis
Jasminum sambac (arabian jasmine)
Juglans (walnuts)
Lablab purpureus (hyacinth bean)
Lactuca sativa (lettuce)
Leucaena leucocephala (leucaena)
Liriodendron tulipifera (tuliptree)
Lolium (ryegrasses)
Macadamia tetraphylla (rough-shell macadamia nut)
Malus domestica (apple)
Mangifera indica (mango)
Manihot esculenta (cassava)
Medicago sativa (lucerne)
Megathyrsus maximus (Guinea grass)
Mesosphaerum pectinatum (comb bushmint)
Mimosa pudica (sensitive plant)
Miscanthus floridulus (japanese silvergrass (USA))
Momordica charantia (bitter gourd)
Mucuna pruriens (velvet bean)
Musa (banana)
Musa acuminata (wild banana)
Musa x paradisiaca (plantain)
Nicotiana tabacum (tobacco)
Olea europaea subsp. europaea (European olive)
Oryza sativa (rice)
Pandanus (screw-pine)
Panicum sumatrense (little millet)
Paspalum conjugatum (sour paspalum)
Paspalum notatum (bahiagrass)
Passiflora edulis (passionfruit)
Pelargonium graveolens (Rose geranium)
Pennisetum clandestinum (Kikuyu grass)
Pennisetum glaucum (pearl millet)
Pennisetum pedicellatum (deenanath grass)
Peony
Persea americana (avocado)
Petunia
Phaseolus vulgaris (common bean)
Phoenix dactylifera (date-palm)
Phytolaccaceae
Pimpinella anisum (aniseed)
Pinus caribaea (Caribbean pine)
Pinus echinata (shortleaf pine)
Pinus elliottii (slash pine)
Pinus massoniana (masson pine)
Pinus patula (Mexican weeping pine)
Pinus taeda (loblolly pine)
Piper nigrum (black pepper)
Pisum sativum (pea)
Platanus occidentalis (sycamore)
Poncirus trifoliata (Trifoliate orange)
Populus heterophylla (Swamp cottonwood)
Prunus domestica (plum)
Prunus dulcis (almond)
Prunus persica (peach)
Prunus salicina (Japanese plum)
Psidium guajava (guava)
Pueraria phaseoloides (tropical kudzu)
Punica granatum (pomegranate)
Pyrus communis (European pear)
Raphanus sativus (radish)
Rosa (roses)
Rosa multiflora (Multiflora rose)
Rubus idaeus (raspberry)
Saccharum edule
Saccharum officinarum (sugarcane)
Schefflera (umbrella tree)
Setaria magna (giant bristlegrass)
Setaria splendida
Solanum lycopersicum (tomato)
Solanum melongena (aubergine)
Solanum torvum (turkey berry)
Solanum tuberosum (potato)
Sorghum bicolor (sorghum)
Sorghum halepense (Johnson grass)
Spinacia oleracea (spinach)
Stylosanthes gracile
Swietenia macrophylla (big leaved mahogany)
Syzygium aromaticum (clove)
Syzygium malaccense (Malay apple)
Tectona grandis (teak)
Theobroma cacao (cocoa)
Tillandsia cyanea
Trifolium alexandrinum (Berseem clover)
Trifolium repens (white clover)
Triticum aestivum (wheat)
turfgrasses
Ulmus parvifolia (lacebark elm)
Urena lobata (caesar weed)
Urochloa decumbens (signal grass)
Urochloa mutica (para grass)
Vaccinium (blueberries)
Vanda
Vanilla planifolia (vanilla)
Vigna mungo (black gram)
Vigna unguiculata (cowpea)
Vitex trifolia
Vitis vinifera (grapevine)
Washingtonia (wshington-palm)
Wisteria
Xanthosoma sagittifolium (elephant ear)
Zea mays (maize)
Zingiber officinale (ginger)
List of symptoms/signs
Leaves  -  abnormal colours
Leaves  -  yellowed or dead
Roots  -  cortex with lesions
Roots  -  necrotic streaks or lesions
Roots  -  reduced root system
Roots  -  soft rot of cortex
Vegetative organs  -  surface lesions or discoloration
Whole plant  -  dwarfing
Whole plant  -  plant dead; dieback
Description
Measurements and morphological descriptions of H. dihystera can be found in Steiner (1945), Das (1960), Roman (1965), Swarup and Sethi (1968), Sher (1966), Siddiqi (1972), Rashid and Khan (1974), Van Den Berg and Heyns (1975) and Fortuner et al. (1981).

Measurements

Topotypes, after Sher (1966).

10 Females: L=590-790 µm; a=27-35; b=5.8-6.9; b'=4.4-5.9; c=35-49; c'=0.8-1.2; V=60-65; stylet=25-28 µm; o=37-46.
Males (extremely rare, 4 males from California, USA): L=590-650 µm; a=25-32; b=5.1-6.1; b'=4.2-4.9; c=31-33; stylet=22-27 µm; spicules=20-23 µm; gubernaculum=7-8 µm.

Topotypes, after Siddiqi (1972).

12 Females: L=610-860 (670) µm; a=26-34 (29.5); b=5.1-6.4 (5.7); b'=4.3-5.2 (4.6); c=40-65 (48); c'=1.0-1.3; V=60-66 (63); stylet=24.5-27.5 (26) µm; o=42-49 (47).

Females: Body spirally curved, more so in posterior region after relaxation or death. Lateral fields with 4 incisures, not areolated. Cephalic region or head hemispherical, with 4-5 annules; framework heavily sclerotized, outer margins extending posteriorly 2-3 body annules. Posterior cephalids distinct, 8-11 annules behind cephalic region. Stylet fairly strong, usually 24-28 µm long, with conus measuring 11.0-12.5 µm long and basal knobs well developed and anteriorly indented. Median oesophageal bulb oval, very muscular, 6-8 body annules long. Orifice of dorsal oesophageal gland at less than half stylet length behind stylet base. Oesophageal glands partially surrounding anterior end of intestine; subventrals slightly longer than the dorsal gland. Excretory pore almost opposite oesophago-intestinal junction. Hemizonid 0-2 annules behind excretory pore. Vulva a transverse slit, at 60-66% of body length. Two branches of reproductive organs outstretched in opposite directions. Ovary with oocytes in a row. Spermatheca offset, empty. Tail dorsally convex-conoid, with or without a slight ventral projection, with 8-12 annules ventrally. Phasmids pore-like, preanal, 5-12 annules anterior to anal level, usually centrally placed in the lateral field; inner incisures of lateral field on tail not fusing distally for some distance.

Males: Extremely rare. Body ventrally arcuate. Head, stylet and oesophagus as in female. Bursa enveloping tail which is conoid.

Juveniles: Four juvenile stages, first occurring within the egg; similar to female in the structure of head, stylet, oesophagus and tail. Different juvenile stages are recognized by the degree of development of the reproductive system: the genital primordia of II, III and IV-stage juveniles have 4, 14 and 108 nuclei respectively (Hirschmann and Triantaphyllou, 1968).

Morphological variations are given by Van Den Berg and Heyns (1975) and Fortuner et al. (1981). SEMs of H. dihystera are given by Marais and Buckley (1992). Ultrastructure of the cuticle is described by Mounport et al. (1993).
Prevention and control

Chemical Control

Combinations of preplant fumigation with postplant foliar sprays were highly effective in suppressing the nematode population over an extended period (Milne et al., 1975, 1977).

Fields of Irish potato in southern Alabama, USA, with severe stem canker (caused by Rhizoctonia solani) and heavily infested with H. dihystera and M. incognita, when treated with sodium azide 1 month before planting gave increases of 10 and 26% and significantly reduced stem canker and spiral nematodes but did not affect M. incognita larvae. 1,3-dichloropropene injected into soil 1 month before planting gave a 26% increase in yield with significant reductions in H. dihystera and M. incognita larvae (Rodriguez-Kabana et al., 1974). 1,3-dichloropropene was effective in controlling H. dihystera, Pratylenchus zeae, Criconemoides sp. and M. incognita in plots growing maize (Singh, 1976a).

H. dihystera, Criconemoides ornatus and Trichodorus christiei were mainly responsible for yield reduction of sweetcorn. Soil treatment with 1,3-dichloropropene increased the average yield of all cultivars by 10%. The use of nematicides and selection of cultivars with some resistance to various nematodes including H. dihystera delays build-up of these pests to damaging levels (Johnson, 1975.).

In Brazil, cocoa cv. Catongo seedlings infested chiefly with H. dihystera and M. incognita and treated with fensulfothion or fosthietan grew better than untreated seedlings (Sharma and Ferraz, 1977b).

Initial populations of Criconemella onoensis as high as 4200 and of H. dihystera as high as 1400 nematodes/litre of soil greatly reduced (between 63 and 72%) yield of paddy rice in Mauritius. Yields were increased by nematicide treatments with 1,3-dichloropropene (Chinappen et al., 1988). In a greenhouse test, anhydrous ammonia applied to a sandy loam soil infested with H. dihystera, Tylenchorhynchus claytoni, Pratylenchus brachyurus and Hoplolaimus galeatus reduced soil populations of T. claytoni and H. dihystera and root populations of H. dihystera and H. galeatus (Rodriguez-Kabana et al., 1981).

Cyromazine, isazofos, isofenphos, seaweed extract and metalaxyl were applied either singly or in combination in two tests to Bermudagrass golf turf (Cynodon dactylon cv. Ormond) parasitized by Hoplolaimus galeatus, Criconemoides spp., H. dihystera, Belonolaimus longicaudatus and Paratrichodorus christiei. Isazofos and isofenphos were effective against some nematodes and seaweed extract markedly improved turf growth although it was not nematicidal (Tarjan and Frederick, 1984a). Bermudagrass turf (Cynodon dactylon) grown on a golf course in Gainesville, Florida, USA and parasitized by several plant nematodes (mainly H. dihystera, Belonolaimus longicaudatus and Paratrichodorus christiei) was treated with nematicides, and isazofos and seaweed extract. The nematicides were significantly superior to the seaweed extract treatment in reducing nematode populations, promoting grass growth and improving root tensile strength. Isazofos with an acute oral LD50 of 60 mg per kg of weight of rats, is appreciably safer than most chemicals currently used for commercial turf nematode control (Tarjan and Frederick, 1984b).

A field experiment in Florida, USA, using the treatments: metam drenched onto the soil and left uncovered; plastic mulch without fumigation; and control, without plastic mulch or fumigation showed, that live numbers of H. dihystera and Rotylenchulus reniformis were reduced within 3 days. Different results were obtained when total numbers (live and dead) were considered, as differences among treatments were not then apparent until 7-12 days after fumigation (McSorley and Parrado, 1984).

Metam applied as a preplant soil drench significantly reduced nematode populations in a site having initial populations (per 100 cm³ soil) of 207 Rotylenchulus reniformis, 29 Meloidogyne incognita, 36 Quinisulcius acutus and 10 H. dihystera. Yield of snap beans (Phaseolus vulgaris) and yellow squashes (Cucurbita pepo) planted in this site were significantly increased by fumigation. The extra crop value usually exceeded the cost of metam applied (McSorley and Pohronezny, 1984).

On groundnut, populations of H. dihystera and H. indicus were selectively influenced by the three herbicides, oxadiazon, fluazifop-butyl and glyphosate. The first two suppressed H. dihystera as well as monocot weed growth but did not significantly affect H. indicus. Both the nematode species were directly influenced by the growth stage of the groundnut crop, with peak populations being attained around late flowering (Patra and Ray, 1987).


Biological Control

The fungus Catenaria anguillulae restricted growth endobiotically in H. dihystera, Tylenchorhynchus brassicae, Hemicriconemoides mangiferae, Hoplolaimus indicus, Aphelenchus avenae and Scutellonema brachyurum without causing death for a few to several days indicating balanced parasitism. Sporangium formation in these species occurred only after the death of nematodes indicating that the fungus is a virulent parasite of nematodes (Singh et al., 1996). Glomus mosseae was found associated with H. dihystera on groundnuts in several localities in Uttar Pradesh, India (Hasan and Jain, 1987).

H. dihystera was preyed upon by soil vampyrellid amoebae, Vampyrella vorax and Arachnula impatiens. The amoebae captured the prey with their fine filopodia, made fine holes in the cuticle by these filopodia and completely emptied the contents of the body of the nematode (Homma and Kegasawa, 1984). The feeding apparatus and gut content of Iotonchus monhystera showed that this mononchid nematode is a predator of H. dihystera (Azmi, 1983)

Pasteuria penetrans parasitized H. dihystera. The hyperparasite develops in the pseudocoelomic fluid into irregular vegetative thalli or filaments, which break up or apparently reproduce asexually into numerous units. At maturity spores develop at the distal ends of dichotomous branches of the thallus, eventually filling the body of the host and causing its death. Spores are disseminated when the host disintegrates (Mankau and Imbriani, 1975).

Host-Plant Resistance

Of various sweetcorn cultivars tested, Seneca 110 and Seneca Explorer were the most resistant and Spancross the most susceptible to nematode injury. The use of nematicides and the selection of cultivars with some resistance to several species of nematodes including H. dihystera delays build-up of these pests to damaging levels (Johnson, 1975).

Six varieties of sugarcane, namely, Co. 312, 997, 647, 1235, 1234 and 1104 that were tested in India were found to be susceptible to H. dihystera (Rao and Swarup, 1974a). In inoculation experiments, three cultivars of Japanese holly (Ilex crenata), Helleri, Convexa and Rotundifolia, were not damaged by H. dihystera (Aycock et al., 1976). In Florida, USA, significantly lower numbers of H. dihystera were present on sweet potato cv. Carver than on Morado and White Triumph after 6 months (McSorley, 1981). Twenty one promising cultivars of sorghum screened against H. dihystera in pot culture experiments showed varying degrees of susceptiblity. Two cultivars, Etawah-2 and JHS-822, were the least susceptible whereas all other cultivars were highly susceptible (Jain and Hasan, 1987). H. dihystera may cause reduction in the resistance of shortleaf pine to Phytophthora cinnamomi by destruction of the structural integrity of the ectomycorrhizal fungal mantle (Marx and Bruehl, 1975).


Cultural Practices and Soil Amendments

Control of H. dihystera, Meloidogyne javanica, Pratylenchus brachyurus and Criconemella ornata in beans (Phaseolus vulgaris) and in maize under field conditions in the Federal District of Brazil was achieved by green manuring with Crotalaria paulina as the most efficient non-chemical control of the nematodes, followed by crop rotation with Tagetes patula (Sharma and Scolari, 1984).

In crop rotation schemes, Cynodon dactylon and Paspalum notatum appeared promising in suppressing H. dihystera populations and so was the continuous cropping of maize with or without rye or Vicia villosa (Brodie et al., 1969). On forage sorghum in India, two vesicular-arbuscular mycorrhizal fungi, Glomus fasciculatum and G. mosseae, were associated with H. dihystera, Pratylenchus zeae and Tylenchorhynchus vulgaris. Where roots had >50% VAM infection the nematode numbers were lower. It is concluded that VAM fungi could be used to manage plant parasitic nematode populations (Jain and Hasan, 1986).

In pineapple land in South Africa, cropping treatment tests showed that nematode populations (mainly H. dihystera, Rotylenchus unisexus and Scutellonema brachyurum) were lowest with Chloris gayana var. Katambora, Desmodium uncinatum and bare fallow, intermediate numbers were found with Eragrostis curvula var. Ermelo, Fescue sp. and Cenchrus ciliaris and highest numbers with Ananas comosus, Phaseolus atropurpureus and grass fallow (Keetch and Dalldorf, 1980). Results of a 3-year rotation scheme showed that populations of H. dihystera and Paratrichodorus christiei were influenced by the fertilization regime of the soil. Nutrient deficiencies resulted in virtual elimination of H. dihystera from plots, and reduced the size of populations of P. christiei (Rodriguez-Kabana and Collins, 1979).

Soil amendment with leaves of neem (Azadirachta indica), datura (Datura fastuosa) and calotropis (Calotropis procera) reduced the population of H. dihystera and improved growth of tomato in Pakistan (Firoza and Maqbool, 1996a, b). Garlic extract (5%) was toxic to H. dihystera and Aphelenchoides composticola (Gupta and Sharma, 1993). Exposure to extract of Punica granatum, Thymus vulgaris and Artemisia absinthium for 72 h reduced the numbers of active nematodes 95.7, 71.4 and 42.9% for H. dihystera, respectively. Exposure to extracts of Citrullus colocynthis and Ricinus communis reduced nematode motility by less than 32% for M. incognita and less than 30% for H. dihystera (Korayem et al., 1993). Aqueous extracts (leaf, seed and pod shell) of Leucaena leucocephala were toxic to M. incognita and H. dihystera to varying degrees (Jain and Hasan, 1984).

Aqueous extracts of fresh leaves, stem and roots of Parthenium hysterophorus were tested against H. dihystera and M. incognita in a laboratory experiment. The aqueous leaf extract killed more nematodes than the root and stem extracts. At the lowest effective concentration of leaf extract, 100% mortality was observed after 48 and 25 h of exposure for H. dihystera and M. incognita, respectively (Hasan and Jain, 1984). On tomato grown with Tagetes patula or T. erecta, M. incognita populations were reduced more than those of H. dihystera, especially at the lowest population level (Vergel et al., 1979). Neem (Azadirachta indica) cake and pressmud (filter cake from cane sugar manufacture) reduced populations of H. dihystera, Pratylenchus coffeae and M. incognita on sugarcane by 81-82% after 90 days (Jonathan et al., 1991).

In Hawaii, USA, H. dihystera population densities declined in pineapple plots planted with marigold, Rhodes grass (Chloris gayana), or in plots left fallow (Ko and Schmitt, 1996). The use of cover plants (oats, Rhodes grass, soyabean and marigold), clean fallow and fallow covered with pineapple-plant residues (mulch) without cover plants, were tried as control methods. Whereas the use of cover plants consistently decreased R. reniformis populations, the effect on H. dihystera was variable, resulting in decreased, unchanged or increased population densities. The change was especially obvious in the oat-cover treatment where H. dihystera population densities increased 9- to 15-fold at the two experimental sites (Ko and Schmitt, 1996). H. dihystera numbers were generally higher in soyabeans following Lolium multiflorum than in those following the control. L. multiflorum cultivars Shannon and Ninak having particularly low numbers of H. dihystera in the soil after 7 weeks. In Festuca arundinacea cv. Kentucky 31F, numbers of H. dihystera and Paratrichodorus minor were lower in plants infected with Acremonium coenophialum [Neotyphodium coenophialum] (Pederson et al., 1988).

Soil infested with H. dihystera, Xiphinema setariae and Meloidogyne incognita was sterilized with hot air, raising the soil temperature up to 100°C for 1 h. Cocoa seedlings grew better in sterilized soil than in the control (Sharma, 1975).

Impact

In a survey of guava orchards in South Africa, 96% of Transvaal plantings and all Cape Province plantings were infected by H. dihystera. In a pot experiment, 4 months after inoculation, the height of nematode infested plants was suppressed by 53.3% compared with the control. Leaf size was also considerably reduced (Willers and Grech, 1986).

In Pakistan, Firoza and Maqbool (1995) found H. dihystera pathogenic to aubergine, tomato and wheat with a population of 1000 nematodes per 250 g soil. It produced chlorosis, stunted growth and sparsely developed roots. In 14 breeding lines of tomato, growth suppression was as high as 49, 69 and 56% in the presence of H. dihystera, Meloidogyne incognita and Pratylenchus penetrans, respectively, and 75% with all three species in combination (Slabaugh, 1974). In the field in Uttar Pradesh, India, 72 cultivars of buffel grass (Cenchrus ciliaris) had high soil populations of H. dihystera and the nematode was pathogenic to C. ciliaris (Jain, 1981). Shoot and root length and shoot and root weight of Leucaena latisiliqua were reduced by 36, 29, 37 and 68%, respectively, at the 1000 inoculum level (Azmi, 1981b).

H. dihystera was pathogenic to Jasminum sambac at 100 nematodes/pot or more (Sundarababu and Vadivelu, 1990). It produced tiny brown necrotic lesions and discolored areas as a result of feeding on roots of Rosa multiflora (Davis and Jenkins, 1960). It was pathogenic to seedlings of cottonwood (Populus heterophylla), American sycamore (Platanus occidentalis) and yellow poplar (Liriodendron tulipifera) (Ruehle, 1971) and to olive seedlings (Diab and El-Eraki, 1968). H. dihystera appeared pathogenic to groundnut and millet in the Sahelian zone of West Africa (Baujard and Martiny, 1995).

In pot tests, with 1000 H. dihystera/plant, cocoa showed stunting and there was a significant decrease in dry root weight (Campelo and Galli, 1980). H. dihystera reduced growth of Capsicum annuum at initial inoculum levels of 50 nematodes/1500 ml soil and above. The rate of multiplication of the nematode was inversely proportional to the initial inoculum level. At the lowest inoculum levels there was an increase in shoot and root weights (Muthukrishnan et al., 1975). An initial population density of 1000 H. dihystera per 500 g of soil growing sugarcane caused significant reduction in fresh weights of shoots, roots and canes, cane length and dry weights of shoots and roots. This may be termed the minimum density level of H. dihystera that would cause noticeable and significant reductions in the growth of sugarcane. A further increase in the initial population level caused still more reduction in crop growth while at lower levels the effect was not noticeable. The nematodes severely damaged the root systems of the sugarcane plants (Rao and Swarup, 1974a). An inoculum level of 10,000 H. dihystera per plant caused significant reduction in plant growth parameters of sorghum (Jain and Hasan, 1987). Pathogenicity studies conducted with H. dihystera showed that this nematode reduced the dry weights of shoot and root of potato cv. Kufri Jyoti by 24-45% while the tuber yields per plant were reduced by 9-17% at 90 days (Pradesh and Singh, 1984).

H. dihystera, Meloidogyne hapla and Pratylenchus penetrans reduced the growth of 'Saranac AR' lucerne seedings when applied at concentrations of 50 nematodes/plant. Nematodes interacted with Pseudomonas viridiflava, P. corrugata and P. marginalis to produce greater growth reductions than were obtained with single pathogens, suggesting synergistic relationships (Bookbinder et al., 1982). Ruehle (1973; 1975) found that H. dihystera and Belonolaimus longicaudatus had no effect on the growth of Pinus palustris seedlings, but a significant reduction in fresh weight of roots was caused by large numbers of Hoplolaimus galeatus and Tylenchorhynchus claytoni, and both root and top weights were reduced by Meloidodera floridensis and Pratylenchus brachyurus.

H. dihystera, Meloidogyne hapla, Paratylenchus projectus, Pratylenchus neglectus and P. penetrans in a range of inoculum densities (425, 850, 1700, 3400 and 6800 nematodes/425 ml of soil) did not affect seedling emergence or total seedling stand of lucerne cultivar Saranac after 3 weeks of growth at 17°C days (16 h) and 14°C nights. Fresh weights of tops and particularly of roots declined as nematode inoculum density increased (Townshend, 1984). H. dihystera caused yield reductions in the soyabean varieties Bragg and Custer, but not in D63-7320, Jackson or D64-4636. Custer appeared to be hypersensitive to the nematode and D64-4636 resistant. A five-fold increase in nematode numbers was recorded on cultivars Bragg, D63-7320 and Jackson (Orbin, 1969). H. dihystera has constantly been found associated with low yields of wheat and peas in the Federal District, Brazil. The nematode provoked significant reduction in dry plant weight and grain weight of both wheat and peas (Sharma et al., 1993). However, in field trials in Florida, USA, no correlation was found between H. dihystera, Quinisulcius acutus or Rotylenchulus reniformis populations and yield of snap bean (Phaseolus vulgaris).


Kassab (1996) found that H. dihystera was predominant in sugarcane fields in Egypt in 1993, followed by Pratylenchus zeae and Hoplolaimus columbus, but in 1994, P. zeae was predominant followed by H. dihystera and H. columbus. Poor sugarcane growth was attributed to nematodes compared with good growth in control plants. H. dihystera, Pratylenchus delattrei and Fusarium solani were involved in a decline of Crossandra undulifolia in Tamil Nadu, India (Srinivasan and Muthukrishnan, 1975).

In experiments it was found that H. dihystera fed on soyabean roots, usually in the region of maturation, avoiding the root tip and preferring tap roots to secondary roots. There was some discoloration and lignin formation in the cell walls immediately around the nematodes but no giant cell formation and it appeared that H. dihystera was not pathogenic to soyabean plants (Orbin, 1973). On cowpea (Vigna unguiculata), H. dihystera consistently increased nodule weight, significantly reduced freshweight and usually had no significant effect on total nitrogen content. In the 33-day experiments, there was evidence for an interaction between the nematodes and Rhizobium with respect to both fresh and nodule weights (Brown, 1972).

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