Plant-parasitic nematodes on pasture in New Zealand

Abstract

White clover (Trifolium repens) fixes nitrogen and provides high-quality feed and is, therefore, a key contributor to New Zealand’s grazed pasture systems. However, its productive potential is rarely reached due to abiotic factors (e.g. drought) and various biotic constraints, including nematodes. In a recurrent selection program based in the greenhouse, resistance to Meloidogyne trifoliophila and Heterodera trifolii has been improved and resistant lines have been crossed to cultivars to improve field performance. Tolerance to root-infecting nematodes and other factors has been improved in a field-based program in which the best performing plants were selected and crossed. 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 among sites and years. This paper summarises progress made in white clover breeding programs in New Zealand and also examines advances in genetic mapping and introgression as they affect resistance to nematodes. The nematodes associated with pasture grasses are reported, together with observations which suggest that root-feeding nematodes have little impact on yield and that the animal toxicity associated with Anguina seed galls in Australia is absent from New Zealand. The effects of infection by endophytic fungi on nematodes parasitising grasses are also reviewed.