PATHOGENICITY OF MELOIDOGYNE JAVANICA ON ASIAN AND AFRICAN RICE

Abstract

Pot experiments were designed to investigate the relationship between initial population densities (Pi) of Meloidogyne javanica (0, 0.125, 0.25, 0.5. 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, or 1024 eggs and juveniles/cm³ soil) and growth of the susceptible Asian rice (Oryza sativa) cv Manifugabo III and the resistant African rice (Oryza glaberrima) cv Hakurt Monton in glasshouse at 25±3 ordm;C. Height and fresh top weight of each plant were measured 50 days after sowing. The data fitted the Seinhorst model, y=m + (1-m) z[supPû[supT], which indicates tolerance limits of rice to M. javanica of 1 and 8 for height of plants and 0.26 and 2.68 eggs and juveniles/cm³ soil for fresh top weight of plants of cv Manifugabo III and cv Hakurt Monton, respectively. Minimum relative fresh top weight and height of cv Manifugabo III was 0 and occurred at Pi = 16 and 64 eggs and juveniles/cm³ soil, respectively; minimum relative fresh top weight and height of cv Hakurt Monton were 0 and 0.2 and occurred at Pi = 256 and 512 eggs and juveniles/cm³ soil, respectively. The maximum reproduction rates of the nematode were 16.2 on cv Manifugabo III and 1.02 on cv Hakurt Monton. Two months after nematode inoculation, infection sites of the resistant cv Hakurt Monton exhibited necrotic tissue and undersized or giant cell formation with consequent suppression of nematode development. In roots of the susceptible cv Manifugabo III giant cells were large and well developed, allowing feeding and regular nematode development.