Feeding sites of Heterodera latipons in wheat, barley and Lolium rigidum were studied and compared with those of Heterodera avenae in wheat. Juveniles of H. latipons penetrated mainly differentiated roots and chose a root cortical cell as their initial syncytium cell (ISC) in wheat and barley, whilst H. avenae chose a vascular parenchymal cell as an ISC. The cell associated with females in wheat root underwent hypertrophy, and incorporated endodermis, pericycle and parenchyma cells of the vascular cylinder by cell wall dissolution. Syncytia of H. latipons contained a high number of organelles, including endoplasmic reticulum, mitochondria, plastids and amoeboid nuclei, whilst those of H. avenae were highly vacuolated. The syncytium partly occupied both the cortex and the vascular cylinder in contrast to those of H. avenae, which occupied most of the space within the vascular cylinder near the infection site. The cortical cell associated with H. latipons males did not undergo hypertrophy, but had dense cytoplasm, and incorporation of other cells by cell wall dissolution was rare. A similar syncytium formation process was observed with barley, but a cortical cell, several cell layers away from the endodermis, was chosen for the ISC. In resistant L. rigidum, H. latipons juveniles chose an endodermal cell or its neighbouring cortical cell as an ISC. Partial dissolution of cell wall was observed in neighbouring parenchymal cells, although the nematode did not develop into adults.
The predatory nematode Koerneria sudhausi reproduced on bacteria that developed spontaneously on a nutrient medium in Petri dishes. The nematode population had a female/male ratio of 2.9 : 1, but female nematodes could reproduce asexually on the bacteria. Each female produced about 60 progeny at 25°C in 9 days without mating. The generation time (egg to egg) at the same temperature was 8 days. Koerneria sudhausi reproduced at 17°C at the same rate as at 25°C, if the bacteria were available as a food source. When the nematode was introduced to a monoxenic culture of Meloidogyne javanica on tomato roots on agar, the nematode fed on second-stage juveniles and eggs. The nematodes introduced to M. javanica-inoculated soil before transplanting tomato seedlings reduced the root galling index in pot experiments. The results suggested that this predatory nematode, K. sudhausi, may serve as a candidate for a biological control agent against root-knot nematodes, because the nematode can be easily cultured on bacteria and achieve a high reproduction rate.
The objective of the present study was to assess if Acrobeloides buetschlii, an opportunistic species common across many soils, can be employed as a suitable model for interactions between free-living soil nematodes and enteric human pathogens. Acrobeloides buetschlii was exposed to mCherry-tagged Salmonella enterica and Escherichia coli O157:H7 and its vector potential was assessed. Salmonella cells were more readily ingested by the nematodes compared to E. coli O157:H7. Adult nematodes ingested more bacteria compared to juveniles. Salmonella survived internally for at least 7 days without affecting the viability of nematodes. Bacterial ingestion by A. buetschlii did not vary for three tested Salmonella serovars but was significantly lower for E. coli O157:H7. Considering the ubiquitous nature of pathogen and vector, these findings suggest that A. buetschlii can serve as a relevant model for studying nematode-Salmonella interactions in an agricultural setting and as potential transport for food-borne pathogens from soil to crops.