A survey of nematodes associated with pyrethrum in Tasmania, Australia, and the susceptibility of pyrethrum cultivars to root-lesion nematode

In a survey of fields in northern Tasmania, Australia, with various cropping histories, root-lesion nematode ( Pratylenchus spp.) was detected in soil from all 99 fields sampled before planting pyrethrum. Population densities were generally low, but seven fields had more than 600 Pratylenchus /200 mL soil, with the maximum density being 3930/200 mL soil. Root-knot nematode ( Meloidogyne spp.) was detected in 20 fields, with only three having population densities greater than 50/200 mL soil. Pratylenchus spp. from a subset of 31 fields were identified to species level, with Pratylenchus crenatus , P. penetrans , P. neglectus and P. thornei occurring in 27, 10, 2 and 3 fields, respectively. In pyrethrum crops aged 1–2 years, root-lesion nematode was recovered from all 70 fields sampled, with 18 fields having more than 300/200 mL soil. The highest population density was 960/200 mL soil. Eighteen fields had more than 200/g fresh weight of root with a maximum of 786/g fresh weight of root. P. crenatus and P. penetrans were extracted from roots of pyrethrum transplants grown for ~3 months in field soil from 8 and 4 of 10 fields, respectively, indicating that pyrethrum was a host of these species. In two pot experiments conducted in the glasshouse, with four commercial pyrethrum cultivars, P. penetrans multiplication rates (the ratio of final to initial nematode population densities) ranged from 2.7 to 7.9 and 2.2 to 6.6.