Plant-parasitic nematodes are annually responsible for an estimated 100 billion euros in crop damage worldwide. Among them, root-knot nematodes (RKN), Meloidogyne spp., including M. incognita, are the most important of the plant parasitic nematodes, infecting almost all cultivated plants, being responsible for billions of euros in crop losses annually (rice, potato, soybean, and legumes). The potential host range of these obligate, sedentary endoparasites encompasses more than 3 000 plant species. M. incognita, representing the most widespread species, is found in every country in which the lowest temperature is more than 3°C and is therefore possibly the most damaging crop pathogen in the world (Trudgill and Block, 2001).
The control of nematodes is often realized by the combination of several pest management strategies. Currently, nematicides, plant resistances and cultural practices are the most important and reliable means of controlling nematodes. Cultural control is widely practised but rotation is of limited value for nematodes with a host range as wide as that of Meloidogyne spp. Resistant cultivars have proven commercially successful, for instance in the control of the most damaging species of Meloidogyne on tomato. Natural host resistance against Meloidogyne spp. has been found in several wild plant species and shown to reduce or suppress nematode development and reproduction. Some dominant resistance genes have been identified and mapped. One of the best characterized nematode resistance genes is Mi which confers resistance to several RKN species in tomato. All the commercially available tomato cultivars resistant to RKN carry the Mi gene, and the emergence of virulent biotypes of nematodes that challenge these resistant cultivars is a serious threat to their future use (Castagnone-Sereno, 2002). Most nematicides are non-specific, notoriously toxic and they pose a threat to the soil ecosystem, ground water and human health. Therefore, the use of agrochemicals is restricted and will be more drastically reduced in the future. For example, methyl bromide, the most commonly used nematicide, was definitively prohibited in Europe in 2005, due to EU regulation. This situation will prevent in most cases the development of viable crops and will strengthen the relevance of studies on nematode pathogenicity factors and the self-defence capability of plants for the implementation of durable and safe cropping systems.
Figure 1. Symptoms of Meloidogyne incognita attack on Ficus roots.
The primary symptom of RKN infection is the formation of typical root galls on the root of susceptible host plants (Fig. 1). Nutrient and water uptake are substantially reduced because of the damaged root- system, resulting in weak and poor-yielding plants. During parasitism, RKN establish and maintain an intimate relationship with their host.
Plant-Nematode interaction team, Inra Paca
Creation date: 13 May 2009
Update: 15 January 2010