Resistance in Trifolium repens and T. semipilosum to Meloidogyne trifoliophila (Nematoda: Tylenchida) is temperature sensitive

Abstract

The clover root‐knot nematode parasitises white clover throughout New Zealand's improved pastures. White clover with partial resistance to this endoparasite has been developed in a recurrent selection programme. Temperatures in the root zone of white clover exceed 25°C each summer and our objective was to determine if resistance was stable at these temperatures. In Experiment 1, clonal copies of resistant and susceptible white clover and Kenya white clover genotypes were planted in inoculated soil and maintained at 25, 28.5 or 32°C. In Experiment 2, resistant and susceptible seed lines of white clover were challenged as seedlings. In Experiment 1, the mean of the root‐knot nematode gall counts on the resistant white clover genotypes was about half that on the susceptible genotypes (P < 0.01) at 25°C, but was not different at the two higher temperatures; similarly on Kenya white clover, resistance was only expressed at 25°C. In Experiment 2, seedlings reflected the pattern shown with copies of genotypes. The breakdown of resistance to the clover root‐knot nematode at these temperatures exacerbates the constraints already placed on clover productivity by the summer drought.