Pasteuria, a bacterial parasite of plant-parasitic nematodes: its occurrence in Australian sugarcane soils and its role as a biological control agent in naturally-infested soil

In a survey of all sugar production areas in Australia, Pasteuria was detected in 56% of the fields sampled. Endospores were seen on root-knot nematode ( Meloidogyne spp.), root-lesion nematode ( Pratylenchus zeae ), stunt nematode ( Tylenchorhynchus annulatus ) and spiral nematode ( Helicotylenchus dihystera ). In most cases infestation levels were relatively low, as less than 5% of the nematodes usually had spores attached. However, the results of a bioassay with soil from a site heavily-infested with P. penetrans suggested that root-knot nematode was being suppressed to some extent at this site. When second-stage juveniles of M. javanica had to move 4 and 8 cm through the soil to reach sugarcane roots, egg production was reduced by 55 and 85%, respectively. Sugarcane had been grown at most of the surveyed sites for more than 100 years but the highest levels of spore encumbrance on root-lesion nematode were observed in two fields that were previously grass pasture and had only grown sugarcane for 18 and 22 years. Pasture and sugarcane soil from one of these sites was bioassayed by inoculating Pratylenchus zeae into soil that had been heated at 60 °C to kill any nematodes present. When the added nematodes were extracted 40 days later, approximately 50% were either parasitised by Pasteuria thornei or had endospores attached, indicating that the biocontrol agent was present at relatively high levels in both soils. Since grazed pastures are never tilled and the two sugarcane fields had been subjected to much less tillage than the other surveyed sites, research should be undertaken to determine whether the tillage practices commonly used in sugarcane are limiting the capacity of Pasteuria thornei to increase to high levels and provide some nematode control.