A seedling based technique for screening for resistance to D. angustus in deep water rice was developed and used to examine components of variability in host suitability. The techniques mimicked natural infection from water and achieved 100 % infection of susceptible check cv. NC492. Approximately 10% of inoculum invaded seedlings, the infective stages being predominantly J3, J4 and adult. Reproduction of D. angustus was rapid on susceptible plants (period of life cycle was 10-20 days at 30 C). Symptom expression and nematode multiplication were studied on a range of resistant and susceptible deep water rice cvs and lines. Resistance is in part conferred by a rapid necrotic response to feeding in the host. The response was exhibited by sorne plants of lines, namely, CNL 319, Bazail65, Rayada l6-02, Rayada l6-03 and Rayada 16-06 to Rayada 16-09, which, in the field, have been consistently resistant across locations and years. The response is qualitatively different from the well known susceptible response and provides a basis for genotypic selection. The relationship between water depth and seedling stature appears to be important in determining infection and early symptom development. D. angustus invades primarily at the water surface so submergence of the leaf sheath delays infection. Symptoms develop more quickly if the water level during infection is adjacent to, or just below, the collar at the top of the leaf sheath. The expression of symptoms and hence early damage is delayed in shallower water.
Gill, J.R.; Plowright, R.A. Aspects of resistance in deepwater rice to the rice stem nematode Ditylenchus angustus. Fundamental and applied nematology (1994) 17 (4) 357-367.