TABLE CONTENTS

SESSION FOUR – RESISTANCE BREEDING AGAINST SEDENTARY
NEMATODES
CONVENORS: PHIL ROBERTS & FOREST ROBINSON
Breeding for Resistance to the Clover Root-knot Nematode and the Clover
Cyst Nematode in White Clover
Mercer, C.F.(1) & N.L. Bell (2)
(1) AgResearch Grasslands, Private Bag 11008, Palmerston North, New Zealand 4442; (2) AgResearch
Ruakura, Private Bag 3123, Hamilton, New Zealand 3240
New Zealand’s pastoral industries produce animal products that are internationally
competitive in spite of the country’s distance from major markets. White clover is a key
contributor to the system as it fixes nitrogen and provides high-quality feed. However,
clover’s potential is rarely reached due to abiotic (e.g., drought) and biotic factors. Chief
among the latter are the clover root-knot nematode (Meloidogyne trifoliophila), clover cyst
nematode (Heterodera trifolii) and lesion nematode (Pratylenchus spp.). Control options
studied have used management and biological options but with most effort in
resistance/tolerance. In a recurrent selection programme based in the greenhouse, resistance
to M. trifoliophila and H. trifolii has been improved and resistant lines crossed to cultivars to
improve field performance. Tolerance to root-infecting nematodes and other factors has been
improved in a field-based programme in which the best-performing plants were selected and
crossed. Resistance to M. trifoliophila and H. trifolii is under polygenic control: resistance
genes for H. trifolii show evidence of dominance whereas resistance genes for M.
trifoliophila show recessiveness. In grazed field trials, lines from both programs performed
as well or better than cultivar controls. Counts of nematodes in roots showed that resistance
reduced numbers but results varied between sites and years. This review paper summarises
progress made in the white clover breeding programs and also examines options in genetic
mapping and introgression as they affect resistance to M. trifoliophila and H. trifolii.
5 th International Congress of Nematology, 2008 13