Plant parasitic nematodes remain a major challenge to crop production that has hitherto received minmum research attention in sub-Saharan Africa. This paper gives the diversity of nematode genera and species associated with cereal crops and indicates the possibility of nemadode population build up due to production intensification especially in soils with high sand content. Twenty-two nematode species from 10 genera of plant parasitic nematodes were recovered in root samples collected from 5 cereal crops (barley, maize, millet, sorghum and wheat) collected from 293 sites in five major cereal growing areas of Uganda (230 maize samples, 18 millet samples, 21 sorghum samples, 18 wheat samples and 6 barley samples), grown singly or as intercrops. Of these, 12 nematode species were encountered in maize roots, namely Aphelenchoides arachides, Aphelenchoides eltaybi, Ditylenchus spp, Helicotylenchus dihystera, Meloidogyne spp., Pratylenchus brachyurus, Pratylenchus goodeyi, Pratylenchus zeae, Scutellonema brachyurus, Scutellonema paralabiatum, Scutellonema clathricaudatum and Rotylenchulus borealis. Based on populations of the nematode species recovered, four distinct nematode groupings were observed: those that were widespread and abundant (Pratylenchus zeae and P. brachyurus); those that were widespread but less abundant (Scutellonema spp., Meloidogyne spp., Rotylenchulus spp. and Helicotylenchus spp.); those that were localized but very abundant (Pratylenchus goodeyi), and those that were localized but less abundant (Aphelenchoides spp. and Ditylenchus spp.). Intensified maize cropping systems with/without noncereal rotations increased risk of Pratylenchus zeae, Scutellonema spp. and Helicotylenchus spp. infection of maize.
Common bean production is constrained by different diseases the major ones being, Angular Leaf Spot (ALS), bean root rot, anthracnose, Common Bright Bacteria (CBB), Bean Common Cosaic Virus (BCMV) and Bean Common Mosaic Necrotic Virus, (BCMNV). The aim of this study was to identify new and better sources of broad resistance to both bean ALS and Root Rot diseases among nutritional bean varieties. Fifty seven varieties were planted in the screen house of CIAT Africa based at Kawanda Agricultural Research Laboratories Institute (KARL). Virulent inocula actually used at CIAT were used to test these genotypes. Different varieties were resistant to specific isolates but interestingly, only ACC 714 contained broad resistance to both Andean and MesoAmerican isolates of bean Angular Leaf Spot as well as Fusarium root rot and Pythium root rot at mean, median and mode basis. Since different nutritional bean varieties have varying levels of resistance to different pathogens, it may be possible to pyramid these resistance genes into appropriate background so as to provide durable resistance in biofortified bean genotypes higher in iron and zinc content.
Insects are a major mode of banana Xanthomonas wilt (XW) spread. High insect activity has been blamed for the high XW incidence in 'Kayinja' (ABB-genome) dominated banana landscapes across east and central Africa. 'Kayinja' male bud nectar composition reportedly contributes to high insect activity. The variation in nectar composition with agro-ecological zones and banana cultivars and its influence on the number of visiting insects in Rwanda were assessed. Three male buds were collected per cultivar for nectar extraction and analysis using a high performance liquid chromatography. Nectar volume and sugar concentrations varied (P<0.001) across 27 banana cultivars, annual seasons and agro-ecological zone. The highest nectar volume was recorded among the East African highland cooking cultivars (AAA-genome) in the high altitude site and the short-heavy rainy season. Nectar contained three sugars: glucose, fructose and sucrose, though hexose (glucose and fructose) was dominant. The three sugars varied significantly (P<0.001) within each cultivar. The total nectar-sugar concentration ranged from 2.3-32%, with the highest among dessert cultivars 'Kamaramasenge' (AABgenome) and 'Gisukari' (AAA-genome). No strong correlation occurred between insect population and total nectar sugar concentration or nectar volume. Insect populations were rather influenced by the weather conditions, the long rainy season characterized by moderate well distributed rainfall recording the highest insect populations as compared to the short rainy season (with heavy rainfall) and the dry seasons.
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