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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).