Nematode interactions in nature : Models for sustainable control of nematode pests of crop plants?

Plant-parasitic nematodes are major crop pests in agro-ecosystems while in nature their impact may range from substantial to no significant growth reduction. The aim of this review is to determine if nematode population control in natural ecosystems may provide us with a model for enhancing sustainable control of nematodes in crops.In agricultural systems, monocultures, narrow rotations, alteration of the soil habitat, and fertilization may alter plant-parasitic nematode dynamics and boost nematode numbers while reducing diversity and effectiveness of top-down control organisms and protective mutualisms (endophytes and arbuscular mycorrhizal fungi). Traditional agro-ecosystems (still applied in tropical regions) involve the development of complex practices such as a broad range of plant species of high genetic diversity grown in associations, rotations, and shifting cultivation, which all influence the complexity of plant-parasitic nematode communities and of control organisms.In nature, plant-parasitic nematodes (and other root feeders and soil pathogens) drive plant community processes, such as succession and plant species diversity. Natural soils contain a wide variety of potential nematode control organisms, but the consequences of this diversity are not known. Wild plant populations also contain more genetic variability than crops, but consequences for coevolution and Red Queen processes for nematode populations have not been studied.We conclude that integrated crop pest control may benefit from studying plant-parasitic nematode-natural antagonist interactions in natural systems, which have been coevolved for longer than crop-nematode-antagonist systems. Understanding how wild plants control their plant-parasitic nematodes may ultimately result in improving the sustainability of crop protection against plant-parasitic nematodes. (c) 2006, Elsevier Inc

Interactions between nematodes and their microbial enemies in coastal sand dunes

European foredunes are almost exclusively colonised by Ammophila arenaria, and both the natural succession and the die-out of this plant have been linked to populations of plant-parasitic nematodes (PPN). The overarching aim of this study was to investigate top-down control processes of PPN in these natural ecosystems through comparative analyses of the diversity and dynamics of PPN and their microbial enemies. Our specific aims were, first, to identify and quantify PPN microbial enemies in European sand dunes; second, to assess their life history traits, their spatial and temporal variation in these ecosystems, and third, to evaluate their control potential of PPN populations. This was done by seasonal sampling of a range of sites and making observations on both the nematode and the microbial enemy communities in rhizosphere sand. Nine different nematode microbial enemies belonging to different functional groups were detected in European sand dunes. Their high diversity in these low productivity ecosystems could both result from or lead to the lack of dominance of a particular nematode genus. The distribution of microbial enemies was spatially and temporally variable, both among and within sampling sites. Obligate parasites, either with low host-specificity or having the ability to form an environmentally resistant propagule, are favoured in these ecosystems and are more frequent and abundant than facultative parasites. Three microbial enemies correlated, either positively or negatively, with PPN population size: Catenaria spp., Hirsutella rhossiliensis and Pasteuria penetrans. Microbial-enemy supported links in the food-web may be involved in the control of PPN populations through indirect effects. The endospore-forming P. penetrans was the most successful top-down control agent, and was implicated in the direct control of Meloidogyne spp. and indirect facilitation of Pratylenchus spp. Overall, our findings suggest strong and diverse top-down control effects on the nematode community in these natural ecosystems.Peer reviewe