Key Nematodes on Food Staples for Food Security in Developing Countries

Cereals constitute the world's most important source of food. Amongst cereals, rice, maize and wheat occupy the most prominent position in terms of production, acreage and source of nutrition, particularly in developing countries (Table 2.1). It has been estimated that about 70% of the land cultivated for food crops is devoted to cereal crops. The global population is projected to increase steadily to around 9 billion by 2050 and with this demand for the staple cereals of rice, maize and wheat will increase (Dixon et al. 2009). Projections suggest that over this period the demand for maize will grow faster than that for wheat due to the use of maize as animal and poultry feed and the increasing demand for biofuel. The demand for wheat will grow faster than that for rice and is likely to follow closely the growth in global population over this period (FAO 2006; Dixon et al. 2009).

In order to meet the expected food demand, further research is required on how to produce more from less. Research will need to also focus on the less understood and appreciated nematodes which are known to be economically important on all three cereal crops. As described above, there is a void of representative information from developing countries for nematodes on many crops, which has affected recognition by the scientific and policy community with respect to agriculture research. As time advances the challenge to meet food security for developing countries is more acute. As their economic situation improves consumption of meat based products is increasing, resulting in greater demands for cereals for animal feed. It is also predicted that there will be reductions in irrigation water for agriculture as the value of this compared with other industries is challenged. This is further compounded by the climate change scenarios and extremes of drought and floods which have been forecast (IPCC 2007).

2.3.1 Maize 2.3.1.1 Introduction

Maize (Zea mays) has the highest production of all three cereal staples (752 Mt). It is grown largely in tropical and subtropical regions with the three largest producers found in North America Asia and Europe (Tables 2.1 and 2.3). Over 60 nematode species have been found associated with maize in different parts of the world. Most of these have been recorded from roots, or soil around maize roots, with information on the biology or pathogenicity of many of these species not readily available. The most important groups of plant parasitic nematodes demonstrated to be important limiting factors in maize production from all over the world include the root knot nematodes, Meloidogyne spp., the root lesion nematodes, Pratylenchus spp. and the cyst nematodes, Heterodera spp. A questionnaire survey to agricultural research institutions in South Africa put Pratylenchus species second overall after root knot nematodes in terms of economic importance (Keetch 1989). Pratylenchus, along with Meloidogyne and Hoplolaimus were the most frequently reported genera on maize in the USA. (Koenning et al. 1999). There are also reports of other plant parasites on maize (Table 2.2), but knowledge of their importance and distribution is limited.

Table 2.2 Plant Parasitic Nematodes of Economic Importance. (Adapted from Handoo 1998) Genus Common Name Type Plant tissue

Primary damage (15)

Table 2.2 Plant Parasitic Nematodes of Economic Importance. (Adapted from Handoo 1998) Genus Common Name Type Plant tissue

Primary damage (15)

Anguina

Seed gall

Migratory endoparasite

Seeds, stems, leaves

Bursaphelenchus

Wilt

Migratory ectoparasite

Seeds, stems, leaves

Criconemella

Ring

Sedentary ectoparasite

Roots

Ditylenchus

Stem and Bulb

Migratory ectoparasite

Stems, leaves

Globodera

Cyst

Sedentary endoparasite

Roots

Helicotylenchus

Spiral

Migratory ecto-,

Roots

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