Survey for root-lesion and stunt nematodes in the northern Australian grain region

Survey for root-lesion and stunt nematodes in the northern Australian grain region

The presence of root-lesion nematodes (Pratylenchus thornei and P. neglectus) and stunt nematode (Merlinius brevidens) in some parts of the northern grain region has been known
since the 1960's and yield loss in wheat caused by P. thornei has been demonstrated since the late 1970's. However, the distribution of P. thornei was considered restricted to the Darling Downs in Queensland and to a few localities in northern NSW. Following the diagnosis of P.
thornei in a wheat crop in a newer cropping area around Goondiwindi in 1996 a more extensive survey of wheat fields was conducted. Soil samples (0-30cm) collected mainly from under wheat crops were processed manually and nematodes extracted by the Whitehead tray method and enumerated under a compound microscope. Out of 795 fields tested from 1996 to 2002, Pratylenchus thornei occurred in 67%, P. neglectus in 32% (both species occurred together in 26%) and no Pratylenchus spp. were detected in 27%. Merlinius brevidens occurred in 73% of fields. Edaphic factors controlling the incidence of these nematodes were tested on 833 samples collected in 1996-7. All three nematode species had a broad pH range, namely from 6.5 to 9.5 for both Pratylenchus spp. and from 6.0 to 9.5 for Merinlius brevidens. All species were detected in soil samples ranging from <20 to 80% clay
and from <20 to >80% sand. However, within this range maximum incidence of P. thornei was in finer textured soils than for P. neglectus. Soil organic carbon had no clearcut effect on the incidence of the species. The incidence of P. neglectus appeared to increase with increasing concentration of DTPA-extractable zinc and bicarbonate–extractable phosphorus in the soil. Observations indicate that P. thornei was spreading in the region in run-off water
and in soil on farm machinery and increasing under intense cropping to wheat.