Ra. Plowright et Jr. Gill, ASPECTS OF RESISTANCE IN DEEP-WATER RICE TO THE STEM NEMATODE DITYLENCHUS-ANGUSTUS, Fundamental and applied nematology, 17(4), 1994, pp. 357-367
A seedling based technique for screening for resistance to D. angustus
in deepwater rice was developed and used to examine components of var
iability in host suitability. The techniques mimicked natural infectio
n from water and achieved 100 % infection of susceptible check cv. NC4
92. Approximately 10% of inoculum invaded seedlings, the infective sta
ges being predominantly J3, J4 and adult. Reproduction of D. angustus
was rapid on susceptible plants (period of life cycle was 10-20 days a
t 30-degrees-C). Symptom expression and nematode multiplication were s
tudied on a range of resistant and susceptible deepwater rice cvs and
lines. Resistance is in part conferred by a rapid necrotic response to
feeding in the host. The response was exhibited by some plants of lin
es, namely, CNL 319, Bazail 65, Rayada 16-02, Rayada 16-03 and Rayada
16-06 to Rayada 16-09, which, in the field, have been consistently res
istant across locations and years. The response is qualitatively diffe
rent from the well known susceptible response and provides a basis for
genotypic selection. The relationship between water depth and seedlin
g stature appears to be important in determining infection and early s
ymptom 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 ju
st below, the collar at the top of the leaf sheath. The expression of
symptoms and hence early damage is delayed in shallower water.