Nematode are microscopic roundworms (typically <1 mm in length) that live in soil, water and plant tissues. Many nematodes are not pests but feed on fungi, bacteria, other nematodes and insects. However, those that are specialised to feed on plants (plant-parasitic nematodes), may cause considerable damage by negatively influencing the water/nutrient transport channels of plants or by damaging their underground vegetative reproductive organs and roots. Nematode damage is usually worse in cases where plants are stressed, since such plants are more susceptible to the pest (Marais & Swart, 2012).
The most important plant-parasitic nematodes on potato in South Africa include the golden cyst nematode (Globodera rostochiensis), root-knot nematode (Meloidogyne spp.) and lesion nematode (Pratylenchus spp.) (Potatoes South Africa, 2017). The root-knot and lesion nematodes are widely distributed in South Africa, although not to the same extent everywhere. The root-knot nematode causes the most damage and yield loss in potato, followed by the lesion nematode. The golden cyst nematode is a quarantine pest found in isolated areas in South Africa.
Currently the ARC-VIMP in collaboration with the ARC-PHP are investigating the relationship between lesion nematodes and the potato early dying disease complex, as well as to characterise different plant-parasitic and free-living nematodes associated with potato.
The diversity in host range and the level of losses makes the root knot nematode (Meloidogyne spp) in sweetpotato to be among the economically important soilborne pathogens. Previously the Meloidogyne pathogens were overlooked mostly due to, general lack of awareness in crop production and the long-term use of nematicides has led to an underestimated effect of these pathogens. However, some chemicals has been discontinued due to harmful effect of chemical residues to the environment. Use of resistant cultivars seem to be the only effective control methods farmers can afford. A glasshouse screening method has been developed in collaboration with Green Biotechnologies Research Centre, University of Limpopo to distinguish resistant and susceptible cultivars (Pofu et al., 2016, 2020). Based on the results obtained, commercial cultivar Bosbok and informal market cultivar Mvuvhelo are resistant to the three most prevalent tropical nematode species (non-host), whilst Blesbok is tolerant (yield not influenced) but is a host to the nematodes. The results are of high impact to the sweet potato growers as the cultivars that are suitable hosts could only be planted where Meloidogyne species are effectively managed.
Contact: Dr Mariette Truter
Pofu, K.M., Mashela, P.W., Laurie, S.M. 2016. Host status to Meloidogyne javanica in sweet potato cultivars: A potential threat in developmental projects. Acta Agriculturae Scandinavica, Section B - Plant Soil Science 67(1):1-5 http://dx.doi.org/10.1080/09064710.2016.1220613 (Aug).
Pofu, K.M., Mashela, P.W., Laurie S. 2020. Host-status of twenty sweet potato lines to Meloidogyne species in South Africa. Acta Agriculturae Scandinavica, Section B - Soil & Plant Science 70(2): 135-139. https://doi.org/10.1080/09064710.2019.1678668.
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