Nematode distribution and damage to yam in central and eastern Uganda

Yams (Dioscorea spp.) are food crops of growing significance in sub Saharan Africa. Unfortunately, nematodes are major pests to their production. A study was undertaken in major yam growing areas of Uganda to investigate the association of plant parasitic nematodes with damage symptoms. Nematodes were assessed from tubers, roots and surrounding soil for seven cultivars belonging to Dioscorea alata, D. bulbisiana, D. burkilliana and D. cayenensis at harvest. Pratylenchus sudanensis was found in the greatest density and was followed byMeloidogyne spp. Higher densities of both nematodes were observed in the tubers rather than roots. Although symptoms of cracking and galling were relatively low, P. sudanensis incidence was strongly associated with cracking and Meloidogyne spp. with galling. Pratylenchus sudanensis and Meloidogyne spp. incidence their associated damage were, however, negatively correlated, suggesting inter-species competition. Principal components analysis of data suggested that differences in susceptibility to P. sudanensis occur between yam cultivars and species

GENOTYPIC VARIATION IN FLATULENCE CAUSING OLIGOSACCHARIDES IN BIOFORTIFIED AND COMMERCIAL DRY BEAN VARIETIES

INTRODUCTION Elimination of flatulence is a challenging practical problem associated with consumption of legumes. The problem is compounded by the variability in susceptibility among individuals. Rackis (1981) established that the oligosaccharides-verbascose, stachyose and raffinose are major causes of flatulence. They escape digestion and are fermented by intestinal micro floral to form excessive amounts of carbon dioxide and hydrogen. Little has been done to develop bean varieties that combine agronomic superiority with nutritional quality, fast cooking and low flatulence levels in eastern Africa. The objectives of this study were to: (i) determine if there is genotypic variation in concentration of oligosaccharides associated with flatulence in commercial bean varieties, recently released biofortified bean and advanced breeding lines, and (ii) the effect of cooking on oligosaccharide concentration. MATERIALS AND METHODS Study materials were 10 commercial dry bean varieties and seven recently released biofortified cultivars representing the Andean and Mesoamerican gene pools and the major market classes grown in east, central and southern Africa. Verbascose, stachyose and raffinose were extracted twice from ground raw and cooked bean milks using a 3:7 v/v methanol-water mixture and quantified on a high performance chromatography system using analytical grade standard reagents. The oligosaccharides sugars were quantified using a high performance liquid chromatography (Chromatography Systems model 750, Shimadzu, USA) with a differential refractometer. The precipitated material was removed by centrifugation and the supernatant filtered prior to analysis. The column used (250mm*4.6mm i.d) was packed with spherisorb-5- amino, as a slurry in propan-2-ol. Sample injection valve, model 7120 was used. The eluting solvent was acetonitrile/water (67:33, v/v) with a flow rate of 2.0 ml min-1 at a temperature of 40°C. Quantification was carried out by peak area comparisons of sample and standards of known concentration (Pinthong et al, 1980). Standards were obtained from SIGMA-Aldrich, USA. Data was analyzed using Genstat statistical software (v15)

Advances in yam and cassava nematology research at IITA

Progress in pest management on cassava (Manihot esculenta) in Africa has witnessed remarkable achievements over recent years in the management of African cassava mosaic virus, cassava mealy bug, cassava green mite and overall germplasm improvement for yield improvements. From the scant information available, root-knot nematodes appear to pose potentially serious constraints to cassava production across Africa. Under heavy infection, 98 % yield losses have been reported and in a survey in Uganda, 100 % of fields observed were infected, yet little attention has been paid to this potential constraint. On yam (Dioscorea spp.), the yam nematode, Scutellonema bradys, is a primary constraint to production and increased adoption of the crop in West Africa. In East Africa the importance of yam has declined over the last few decades and efforts to increase its promotion are hampered by nematode pests. S. bradys has to date not been observed in East Africa, but Pratylenchus sudanensis has been identified, causing similar damage to S. bradys. Meloidogyne spp. also appear to be particularly damaging to introduced, high-yielding yam lines. Screening against these nematodes is currently in progress. Research at the IITA in East and West Africa has made progress towards improved knowledge on these pests. These include initiating work on the biology and epidemiology of P. sudanensis on yam, improving our knowledge of Meloidogyne spp. important on cassava, expanding information on the distribution and incidence of nematode pests on these crops and development of management options against them

Damage to yam (Dioscorea spp.) by rootknot nematode (Meloidogyne spp.) under field and storage conditions in Uganda

Although root-knot nematodes (Meloidogyne spp.) are a widely distributed pest of yam (Dioscorea spp.), the level of damage the yams incur, either alone or in association with other plant-parasitic nematodes is largely undetermined. The current study assessed the damage Meloidogyne spp. caused in the field and during storage, following inoculation onto clean seed material and also to yam planted into infested fields. In general, Meloidogyne spp. caused little galling to roots and tubers, and limited reduction in plant growth and yield. Of three species tested, D. rotundata was the most susceptible and most heavily affected by Meloidogyne spp. infection, D. alata was the least affected, and D. cayenensis was intermediately affected yam species. Meloidogyne spp. infection of tubers significantly exacerbated yam tuber weight loss during storage, particularly during the first 2 months, and moreover reduced and delayed tuber sprouting. Farmers need to select tubers free of Meloidogyne spp. symptoms prior to storage to reduce losses from tuber deterioration, and while selecting planting material for the succeeding season

Evaluation of yam host-plant response to rootknot nematodes in Uganda

A field trial was established at Sendusu. 40 km north of Kampala. Uganda, to evaluate the response of yarn lines, developed by the International Institute of Tropical Agriculture (IITA), to nematode infestation. The field was naturally infested with nematodes and plants were established from tissue culture. Harvested yam tubers were infested mainly with Meloidogyne javanica and, to a lesser extent, with Pralylenchus spp.; Scutonel/onema sp., Rolylenchulus sp. and HelicOlylenchus sp. were round occasionally. Line TOR 87/00559 OP (38) supported the highest population 01 M javanica juveniles, while lines TDR 87/00571 OP {71} and TDR 91/00121 OP {22} did not support any nematode species, suggesting the existence 01 resistance to root•knot nematodes in the IITA germplasm collection

Nematode Distribution and Damage to Yam in Central and Eastern Uganda

Yams ( Dioscorea spp.) are food crops of growing significance in sub Saharan Africa. Unfortunately, nematodes are major pests to their production. A study was undertaken in major yam growing areas of Uganda to investigate the association of plant parasitic nematodes with damage symptoms. Nematodes were assessed from tubers, roots and surrounding soil for seven cultivars belonging to Dioscorea alata , D. bulbisiana , D. burkilliana and D. cayenensis at harvest. Pratylenchus sudanensis was found in the greatest density and was followed by Meloidogyne spp. Higher densities of both nematodes were observed in the tubers rather than roots. Although symptoms of cracking and galling were relatively low, P. sudanensis incidence was strongly associated with cracking and Meloidogyne spp. with galling. Pratylenchus sudanensis and Meloidogyne spp. incidence their associated damage were, however, negatively correlated, suggesting inter-species competition. Principal components analysis of data suggested that differences in susceptibility to P. sudanensis occur between yam cultivars and species.Les ignames ( Dioscorea spp.) sont une culture alimentaire d'importance croissante en Afrique sub–saharienne. Malheureusement, les nématodes sont des parasites majeurs qui gênent sa production. Une étude était menée dans les principales régions productrices de l'igname en Ouganda en vue de pouvoir mener investigation sur l'association des nématodes parasitant les plantes avec les symptômes de dommages. Les nématodes étaient évalués à partir des racines, tubercules, et sol environnant pour 7 cultivars appartenant à Dioscorea alata , D. bulbisiana , D. burkilliana et D. cayenensis à la récolte. Pratylenchus sudanensis était considérée l'espèce à plus haute densité et était suivie par Meloidogyne spp. Des densités plus élevées des nématodes étaient observées plus dans les tubercules que dans les racines. Bien que les symptômes de craquelures et d'irritations étaient relativement bas, P. Sudanensis et Meloidogyne spp. étaient respectivement associées à la craquelure et à l'irritation. Pratylenctus Sudanensis et Meloidogyne spp. présentaient des damages associés, qui étaient cependant négativement corrélés suggérant une compétition inter-espèces. L'analyse principale des données a suggéré des différences à la susceptibilité du P. Sudanensis surviennent entre cultivars et espèces d'ignames

Nematode distribution and damage to yam in Central and Eastern Uganda

Yams (Dioscorea spp.) are food crops of growing significance in sub Saharan Africa. Unfortunately, nematodes are major pests to their production. A study was undertaken in major yam growing areas of Uganda to investigate the association of plant parasitic nematodes with damage symptoms. Nematodes were assessed from tubers, roots and surrounding soil for seven cultivars belonging to Dioscorea alata, D. bulbisiana, D.burkilliana and D. cayenensis at harvest. Pratylenchus sudanensis was found in the greatest density and was followed by Meloidogyne spp. Higher densities of both nematodes were observed in the tubers rather than roots. Although symptoms of cracking and galling were relatively low, P. sudanensis incidence was strongly associated with cracking and Meloidogyne spp. with galling. Pratylenchus sudanensis and Meloidogyne spp. incidence their associated damage were, however, negatively correlated, suggesting inter-species competition. Principal components analysis of data suggested that differences in susceptibility to P. sudanensis occur between yam cultivars and species.Les ignames (Dioscorea spp.) sont une culture alimentaire d’importance croissante en Afrique sub–saharienne.Malheureusement, les nématodes sont des parasites majeurs qui gênent sa production. Une étude était menéedans les principales régions productrices de l’igname en Ouganda en vue de pouvoir mener investigation surl’association des nématodes parasitant les plantes avec les symptômes de dommages. Les nématodes étaientévalués à partir des racines, tubercules, et sol environnant pour 7 cultivars appartenant à Dioscorea alata, D.bulbisiana, D. burkilliana et D. cayenensis à la récolte. Pratylenchus sudanensis était considérée l’espèce à plushaute densité et était suivie par Meloidogyne spp. Des densités plus élevées des nématodes étaient observéesplus dans les tubercules que dans les racines. Bien que les symptômes de craquelures et d’irritations étaientrelativement bas, P.Sudanensis et Meloidogyne spp. étaient respectivement associées à la craquelure et à l’irritation.Pratylenctus Sudanensis et Meloidogyne spp. présentaient des damages associés, qui étaient cependant négativementcorrélés suggérant une compétition inter-espèces. L’analyse principale des données a suggéré des différences à lasusceptibilité du P. Sudanensis surviennent entre cultivars et espèces d’ignames

Assessing nutritional diversity of cropping systems in African villages

Background: In Sub-Saharan Africa, 40% of children under five years in age are chronically undernourished. As new investments and attention galvanize action on African agriculture to reduce hunger, there is an urgent need for metrics that monitor agricultural progress beyond calories produced per capita and address nutritional diversity essential for human health. In this study we demonstrate how an ecological tool, functional diversity (FD), has potential to address this need and provide new insights on nutritional diversity of cropping systems in rural Africa. Methods and Findings: Data on edible plant species diversity, food security and diet diversity were collected for 170 farms in three rural settings in Sub-Saharan Africa. Nutritional FD metrics were calculated based on farm species composition and species nutritional composition. Iron and vitamin A deficiency were determined from blood samples of 90 adult women. Nutritional FD metrics summarized the diversity of nutrients provided by the farm and showed variability between farms and villages. Regression of nutritional FD against species richness and expected FD enabled identification of key species that add nutrient diversity to the system and assessed the degree of redundancy for nutrient traits. Nutritional FD analysis demonstrated that depending on the original composition of species on farm or village, adding or removing individual species can have radically different outcomes for nutritional diversity. While correlations between nutritional FD, food and nutrition indicators were not significant at household level, associations between these variables were observed at village level. Conclusion: This study provides novel metrics to address nutritional diversity in farming systems and examples of how these metrics can help guide agricultural interventions towards adequate nutrient diversity. New hypotheses on the link between agro-diversity, food security and human nutrition are generated and strategies for future research are suggested calling for integration of agriculture, ecology, nutrition, and socio-economics