Chitambo, Oliver: African nightshade and African spinach: A neglected and underutilized resource with significant potential to manage plant-parasitic nematodes. - Bonn, 2019. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
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author = {{Oliver Chitambo}},
title = {African nightshade and African spinach: A neglected and underutilized resource with significant potential to manage plant-parasitic nematodes},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2019,
month = may,

note = {African indigenous vegetables (AIV) are essential for dietary diversification and ensuring nutritional requirements for people in sub-Sahara Africa. AIV have been largely marginalized by agriculture research, yet they are hardy and tolerant to varying environmental conditions. Plant-parasitic nematodes particularly root-knot nematodes (RKN: Meloidogyne spp.) and cyst nematodes (CN: Globodera and Heterodera spp.) cause severe yield reduction on most cultivated crops and are of high economic importance. Despite the significance of nematode surveys and diagnosis, the occurrence and correct identity of RKN and potato cyst nematodes (PCN) on AIV such as African nightshade (Solanum spp.) and African spinach (Amaranthus spp.) remains largely unknown. In Chapter 2 and 3, a survey was conducted in Kenya and a DNA barcode based assay was used to identify RKN and PCN species. Our survey revealed that S. villosum exhibited high root galling whereas on S. scabrum, A. cruentus, and A. dubius root galling was rare or very low. Moreover, soil collected from the rhizosphere of S. villosum and S. scabrum contained few cysts of PCN and no developing PCN females were observed on the roots of growing plants. The resulting RKN and PCN mitochondrial DNA haplotypes are globally distributed, indicating that areas of high native nematode species richness (RKN species) are not resistant to colonization by alien nematode species (PCN species). In this context we detected RKN - PCN co-infection in potato and RKN - RKN co-infection in tomato and Parthenium hysterophorus (an invasive weed in Africa). In Chapter 3, the dynamics of RKN and PCN on A. dubius, A. cruentus, S. scabrum, and S. villosum over 2 years was studied in a field experiment at KALRO, Kenya. The effects of AIV crop species on RKN and PCN soil infestation were evaluated using susceptible S. lycopersicum or S. tuberosum. After the successive cultivation of A. dubius and S. scabrum our results show that RKN soil infestation decreased by 85%, whereas S. scabrum and S. villosum decreased PCN by more than 80%. When cropping susceptible crops, after three seasons of successive cultivation of these AIV, galling index and number of developing PCN females measured on susceptible crops decreased by more than 75%. Wilting incidences and RKN-PCN co-infection incidences also decreased significantly. In Chapter 4, the resistance mechanism of African nightshade and African spinach to RKN and PCN species was studied. We showed that successful parasitism was impaired by localized root tissue necrosis and disintegration during the early stages of nematode infection in resistant African nightshade and African spinach. Notably, A. dubius (broad leaf) showed full resistance to M. enterolobii, a highly pathogenic nematode known for overcoming plant resistance in most cultivated crops. For PCN, both S. scabrum and S. villosum stimulated PCN hatching but not their reproduction with a similar mechanism of resistance as proposed before. These findings reveal that nematode resistant AIV evolved cellular self-destruction of root tissue as a mechanism for defense against RKN and PCN. In that way, a cell suicide process orchestrates the containment, starving, and expulsion of parasitic nematodes. Inevitably, the information generated in this study is important in breeding programmes, designing crop rotation schemes, and cropping systems in order to avoid yield losses caused by high RKN and PCN soil infestation. This will help to support the implementation of a productive and effective integrated pest management strategy that is needed to meet the nutritional requirements of people in sub-Saharan Africa.},
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