NOTES ON TAXONOMY AND BIOLOGY: Heterodera oryzae is morphological similar to H. elachista, H. oryzicola and H. sacchari. The morphological separation of these cyst nematodes is difficult. Morphological features and biochemical characters of diagnostic value are used for the separation of these species (Nobbs et al., 1992). This cyst forming nematode has sedentary endoparasitic habits. Cysts are persistent tanned sacs derived from the female body and contain the eggs. Cysts persist in soil for many years. Second-stage juveniles (J2) emerge from the cysts, penetrate host roots, and establish a specialized feeding site (syncytium) in the stele. They develop into swollen females, which retain the eggs and produce large egg masses. Females rupture root cortex and protrude from root surface. At the end of the reproductive phase, females die and become ovoid dark or black cysts. These cysts are ambifenestrate and are provided of a long vulval slit, rounded semifenestra, bullae and a well developed underbridge without finger-like projections (Nobbs et al., 1992).
GEOGRAPHIC DISTRIBUTION: Bangladesh, Gambia, India, Ivory Coast, Liberia, Pakistan, and Senegal. This species has been reported in Japan, but this identification is uncertain because of the similiraty of this species with H. elachista a nematode pest of rice in Japan.
HOSTS: Rice (Oryza sativa) is the primary host of this species. Other hosts include; plantain (Musa paradisiaca.), corn (Zea mays), Cyperus umbellatus elephant grass (Pennisetum purpureum) and plantain (Musa paradisiaca.). Results of host tests indicate that sugar cane, sorghum and millet are not parasitized by this nematode (Luc, 1986).
CROP LOSSES: The damage induced by this nematode has not been quantified. It is considered to be less aggressive than Heterodera sacchari on rice (Luc, 1986).
MEANS OF MOVEMENT AND DISPERSAL: This cyst nematode is dispersed with soil debris and plant material contaminated by the cysts.
RATING: (L) Taking into consideration the limited host range and information on the economic damage caused by this nematode, a low priority rating was given for completing a complete PRA.
CAB International. 2001. Heterodera oryzaein Crop protection compendium, global module, 3rd edition. Wallingford, UK: CAB International.
Luc, M. 1986. Cyst nematodes in equatorial and hot tropical regions Pp.355-372. in F. Lamberti and C.E. Taylor, eds. Cyst nematodes. New York and London: Plenum Press.
Luc, M. and D.P. Taylor. 1977. Heterodera oryzae, CIH descriptions of plant parasitic nematodes, Set 7, No. 91. St. Albans, UK: Commonwealth Institute of Helminthology.
Nobbs, J. M., S. K. Ibrahim, and J. Rowe. 1992. A morphological and biochemical comparison of the four cyst nematodes species, Heterodera elachista, H. oryzicola, H. oryzae, and H. sacchari (Nematoda:Heteroderidae) known to attack rice. Fundamental and Applied Nematology 15:551-562.