Improvement of accession distinctiveness as an added value to the global worth of the yam (Dioscorea spp) genebank

Open Access JournalMisidentification of accessions is a common problem in genebanks. Along the years, mistakes accumulate and this is particularly true when dealing with a large number of accessions requiring annual regeneration. Human errors such as mislabeling or misreading and material mix up during planting or storage are the main causes for misidentification of accessions. The international collection of yam, maintained at IITA, has accumulated ‘non true to type’ accessions along the years. In the present study, 53 morphological descriptors were used to detect uniformity of individuals within accessions of the yam gene bank collection i.e. agro morphological mismatch between individual plants of the same accession. Based on a similarity matrix, individual pairs with less than 0.90 similarity coefficients, which varies in six descriptors and more, were considered as distinct and mismatched, whereas those that had similarity coefficients greater than or equal to 0.90 were considered as clones from the same parent. Overall, 20.60% of the total 3156 accessions were found not true to type i.e., misidentified individuals. The descriptive analysis shows that morphological traits like distance between lobes, upward folding of leaf along main vein, young stem color, old stem color, leaf shape, leaf density and plant vigor are the most discriminative descriptors for individual identification within accession. Some other traits were also found species specific and they may aid in distinguishing misidentifications between species

Sensitivity of Prostephanus truncatus (Horn) (Coleoptera:Bostrichidae) flight activity to environmental variables in Benin, West Africa

Published online: 01 Dec 2001Based on pheromone trap catches, a model of weekly Prostephanus truncatus (Horn) flight activity was generated for southern Benin. Using response surface regression, the following environmental variables were examined: number of rainy days per week, precipitation, minimum and maximum temperatures, minimum relative air humidity, and daylength. A time-variable, year, was included to account for the variance between years. From step-wise exclusion of variables with the lowest contribution to the model fit, a model was generated which included three environmental variables (daylength, minimum relative air humidity, and minimum temperature) that explained 55% of the total variance, and the yearly variable explaining 8%. The response surface regression analysis of P. truncatus flight activity revealed the following: (1) it was positively correlated with daylength when daily minimum temperature and relative air humidity were low, (2) it was positively associated with minimum relative air humidity when lower than 75%, (3) it was negatively associated with minimum temperature, (4) unexplained yearly variation was important for the predictive strength of the model, (5) interactions of environmental variables contributed substantially to the model fit, and (6) precipitation, both as mm rain and as number of rainy days, had little influence on P. truncatus flight activity. Independent data showed that the model predicted P. truncatus flight activity well elsewhere in southern Benin, whereas in central Benin new coefficients for the same environmental variables were needed to produce an adequate prediction. The model did not fit pheromone baited trap catches from northern Benin

Distribution, prevalence, and severity of damages caused by nematodes on yam (Dioscorea rotundata) in NIssathme30igeria

Nigeria is the main yam-growing country of the world. In the country, various plant-parasitic nematodes have been reported constraining yam production and the storability of tubers. This study established the damage level of nematodes on white yam tubers (Dioscorea rotundata) across the major production areas in the country for management purposes. Incidence and severity of symptoms (cracking, dry rot, and galling) associated with nematodes were assessed on 1,114 yam heaps (181 vendors) from 23 markets and on 2,502 tubers from 26 farmer storage areas (yam barns) in the Humid Forest (HF), Derived Savanna (DS) and Southern Guinea Savanna (SGS) agro-ecological zones (AEZ). On yam heaps, the symptom incidence averaged 55%, 35%, and 6% for galls, dry rot, and for cracks, respectively. Only the incidence of dry rot was significantly different (P<0.0001) across the AEZ. On yam tubers, the incidence averaged 24%, 8%, and 2% for galls, dry rot, and for cracks, respectively. The incidence for galls was higher in the SGS than in the DS (P=0.0018) whereas the incidence of cracks was higher in the DS than in the SGS (P=0.0080). The actual values of symptom severity were, in general, low in the AEZ compared with the predicted values except for dry rot. A significant positive correlation was found between galls and Meloidogyne and between dry rot and Scutellonema. Pratylenchus was also recovered from a few yam tubers; however, no link with symptoms on yam tubers could be established. Vendors and farmers, based on the answers from a questionnaire, were very familiar with nematode symptoms on yam tubers, but awareness of nematodes was low. This study shows that Meloidogyne and Scutellonema are the major nematode constraints to yam production in the three AEZ of Nigeria and calls for effective yam nematode management in Nigeria and in other yam-producing countries

Distribution, prevalence, and severity of damages caused by nematodes on yam (Dioscorea Rotundata) in Nigeria

Open Access ArticleNigeria is the main yam-growing country of the world. In the country, various plant-parasitic nematodes have been reported constraining yam production and the storability of tubers. This study established the damage level of nematodes on white yam tubers (Dioscorea rotundata) across the major production areas in the country for management purposes. Incidence and severity of symptoms (cracking, dry rot, and galling) associated with nematodes were assessed on 1,114 yam heaps (181 vendors) from 23 markets and on 2,502 tubers from 26 farmer storage areas (yam barns) in the Humid Forest (HF), Derived Savanna (DS) and Southern Guinea Savanna (SGS) agro-ecological zones (AEZ). On yam heaps, the symptom incidence averaged 55%, 35%, and 6% for galls, dry rot, and for cracks, respectively. Only the incidence of dry rot was significantly different (P<0.0001) across the AEZ. On yam tubers, the incidence averaged 24%, 8%, and 2% for galls, dry rot, and for cracks, respectively. The incidence for galls was higher in the SGS than in the DS (P=0.0018) whereas the incidence of cracks was higher in the DS than in the SGS (P=0.0080). The actual values of symptom severity were, in general, low in the AEZ compared with the predicted values except for dry rot. A significant positive correlation was found between galls and Meloidogyne and between dry rot and Scutellonema. Pratylenchus was also recovered from a few yam tubers; however, no link with symptoms on yam tubers could be established. Vendors and farmers, based on the answers from a questionnaire, were very familiar with nematode symptoms on yam tubers, but awareness of nematodes was low. This study shows that Meloidogyne and Scutellonema are the major nematode constraints to yam production in the three AEZ of Nigeria and calls for effective yam nematode management in Nigeria and in other yam-producing countries. RESUMEN Nigeria es el principal país productor de ñame del mundo. En el país, se ha informado que varios nematodos fitoparásitos restringen la producción de ñame y la capacidad de almacenamiento de los tubérculos. Esta investigación se realizó para establecer el nivel de daño de nematodos en tubérculos de ñame blanco (Dioscorea rotundata) en las principales áreas de producción de ñame en el país para un propósito de gestión adecuado. La incidencia y severidad de los síntomas (grietas, pudrición seca y agallas) fueron evaluados en 1,114 pilas de ñame de 181 vendedores en 23 mercados; y de las 26 áreas de almacenamiento de ñame de los agricultores, la evaluación se realizó mediante la observación de 2502 tubérculos en tres zonas agro-ecológicas (ZAE): el bosque húmedo (BH), la sabana derivada (SD) y la sabana guinea del sur (SGS). La incidencia en las pilas de ñame fue en promedio de 55%, 35% y 6% para agallas, pudrición seca y grietas, respectivamente. Solo hubo diferencia significativa en la incidencia de la pudrición seca (P <0,0001) a lo largo de la ZAE. La incidencia de síntomas en los tubérculos en las áreas de almacenamiento fue de en promedio de 24%, 8% y 2% para agallas, pudrición seca y grietas, respectivamente. La incidencia de agallas fue significativamente alta en el SGS que en el DS (P = 0.0018), mientras que la incidencia de grietas fue significativamente alta en el DS que en el SGS (P = 0.0080). Los valores reales de la severidad de los fue en general baja en los tres ZAE en comparación con los valores predichos a excepción de la pudrición seca. Una correlación positiva significativa se encontró entre agallas y la densidad de Meloidogyne y entre la pudrición seca y la densidad Scutellonema. También se obtuvieron nematodos del género Pratylenchus en los tubérculos de ñame, sin embargo, no se pudo establecer una relación con los síntomas. Los vendedores y los agricultores, según las respuestas del cuestionario, estaban muy familiarizados con los síntomas de nematodos en los tubérculos de ñame, pero el conocimiento de nematodos fue escaso. Este estudio muestra claramente que los nematodos en el ñame plantean grandes limitaciones a la producción de ñame en las tres zonas agro-ecológicas de Nigeria. Esto requiere de un manejo efectivo de los nematodos del ñame en Nigeria y en otros países productores de ñame

Increasing cassava root yield on farmers’ fields in Nigeria through appropriate weed management

Open Access Article; Published online: 08 Sep 2021Weed competition is the major biological stress affecting cassava production in smallholder farms in West and Central Africa, where yields are low compared with those in Asia and Latin America. Options for improved weed management are crucial in increasing productivity. Selected pre- and post-emergence herbicides, integrated with appropriate tillage and plant spacing, were tested in 96 sites in four locations in Nigeria, 24 in 2016 and 72 in 2017. Trials were split plots with six pre-emergence herbicides and no post-emergence treatment as main plots. Subplot treatments were four post-emergence herbicides, weeding with a motorized rotary weeder, short- and long-handled hoes, and no post-emergence weed control, i.e., regardless of pre-emergence treatments. Indaziflam-based treatments, irrespective of post-emergence treatment, and flumioxazin + pyroxasulfone applied pre-emergence followed by one weeding with a long-handled hoe provided >80% control of major broadleaf and grass weeds. Compared with herbicide use, farmer control practices (53%) were not efficient in controlling weeds. The highest root yield was produced where (1) s-metolachlor was combined with atrazine, and one weeding with a long-handled hoe or clethodim with lactofen, and (2) indaziflam + isoxaflutole was combined with glyphosate. An increase in root yield from 3.41 to 14.2 t ha-1 and from 3.0 to 11.99 t ha-1 was obtained where herbicides were used compared with farmers’ practice and manual hoe weeding. Our results showed that integrating good agronomic practices with safe and effective use of appropriate herbicides can result in root yield >20 t ha−1. i.e., twice the national average root yield of 8–12 t ha−1, with >50% net profit. The use of appropriate herbicides can reduce the amount of manual labor required and improve livelihoods, specifically for women and children. Smallholder cassava farmers would require continuous training on the safe use and handling of herbicides to improve efficiency and prevent adverse effects on humans and the environment

Screening preemergence herbicides for weed control in cassava

Open Access ArticleWeed competition severely constrains cassava root yield in sub-Saharan Africa; thus, good weed control measures, including the use of herbicides, are increasingly important. Herbicide trials were conducted at five locations across eastern, western, and north-central Nigeria over two cropping seasons (2014 and 2015). Nineteen premixed PRE herbicides applied at different rates were evaluated for efficacy on weeds and selectivity on cassava. Manual hoe-weeding at 4, 8, and 12 wk after planting (WAP) and two S-metolachlor + atrazine treatments commonly used by cassava growers were included for comparison. Six of the 19 PRE herbicide treatments (indaziflam + isoxaflutole, indaziflam + metribuzin, flumioxazin + pyroxasulfone, isoxaflutole, acetochlor + atrazine + terbuthylazine, and terbuthylazine + S-metolachlor) consistently provided 80% to 98% broadleaf and grass weed control up to 8 wk after treatment. Overall, PRE herbicide treatments and cassava yield were significantly positively correlated. Herbicide treatments terbuthylazine + S-metolachlor, flumioxazin + pyroxasulfone, diflufenican + flufenacet + flurtamone (respectively, 60 + 60 + 60, 120 + 120 + 120, 90 + 360 + 120, and 135 + 360 + 180 g ha−1), acetochlor + atrazine + terbuthylazine (875 + 875 + 875 g ha−1), S-metolachlor + atrazine (870 + 1,110 g ha−1), oxyfluorfen (240 g ha−1), indaziflam + isoxaflutole (75 + 225 g ha−1), indaziflam + metribuzin (75 + 960 g ha−1), and aclonifen + isoxaflutole (500 + 75 g ha−1) contributed to yields exceeding twice the Nigerian national average of 8.76 tonnes ha−1. These treatments had root yields of 1.4 to 2 times higher than plots that had been hoe-weeded three times. There were some adverse herbicide treatment effects such as delayed cassava sprouting and temporary leaf bleaching observed in indaziflam and diflufenican + flufenacet + flurtamone treatments, whereas sulfentrazone caused prolonged leaf crinkling. The PRE applications alone at rates safe for cassava did not provide adequate season-long weed control; supplemental POST weed control is needed about 10 WAP for satisfactory season-long control

Metabolites identified during varied doses of aspergillus species in Zea mays grains, and their correlation with aflatoxin levels

Open Access Journal; Published online: 7 May 2018Aflatoxin contamination is associated with the development of aflatoxigenic fungi such as Aspergillus flavus and A. parasiticus on food grains. This study was aimed at investigating metabolites produced during fungal development on maize and their correlation with aflatoxin levels. Maize cobs were harvested at R3 (milk), R4 (dough), and R5 (dent) stages of maturity. Individual kernels were inoculated in petri dishes with four doses of fungal spores. Fungal colonisation, metabolite profile, and aflatoxin levels were examined. Grain colonisation decreased with kernel maturity: milk-, dough-, and dent-stage kernels by approximately 100%, 60%, and 30% respectively. Aflatoxin levels increased with dose at dough and dent stages. Polar metabolites including alanine, proline, serine, valine, inositol, iso-leucine, sucrose, fructose, trehalose, turanose, mannitol, glycerol, arabitol, inositol, myo-inositol, and some intermediates of the tricarboxylic acid cycle (TCA—also known as citric acid or Krebs cycle) were important for dose classification. Important non-polar metabolites included arachidic, palmitic, stearic, 3,4-xylylic, and margaric acids. Aflatoxin levels correlated with levels of several polar metabolites. The strongest positive and negative correlations were with arabitol (R = 0.48) and turanose and (R = 0.53), respectively. Several metabolites were interconnected with the TCA; interconnections of the metabolites with the TCA cycle varied depending upon the grain maturity

Aflatoxin contamination in Tanzania: quantifying the problem in maize and groundnuts from rural households

Published online: 28 Apr 2021Aflatoxins are toxic and carcinogenic secondary metabolites, produced by Aspergillus flavus and Aspergillus parasiticus, which contaminate food and feed and threaten human and animal health. To assess the prevalence of aflatoxins in Tanzania, 180 groundnut and 200 maize samples were collected from 9 and 10 districts, respectively. Aflatoxin contamination was quantified using high performance liquid chromatography. Aflatoxins were detected in samples collected from all districts and prevalence ranged from 92 to 100% for groundnuts and 10 to 80% for maize. The mean aflatoxin level for groundnuts was 6.37 μg/kg and the highly contaminated sample had 40.31 μg/kg. For maize, the mean aflatoxin level was 12.47 μg/kg and the highly contaminated sample had 162.40 μg/kg. The estimated average probable daily intake (APDI) of aflatoxin B1 (AFB1) from groundnuts consumption was 1.88 ng/kg body weight/day, while for maize, it ranged between 151.98-272.89 ng/kg body weight/day. The APDI for both groundnut and maize exceeded the provisional maximum tolerable daily intake (PMTDI) of AFB1 for adults (1 ng/kg body weight/day), bringing about health concerns for populations in Tanzania. Another alarming finding was that 75% of the farmers who provided samples for analysis were not aware of aflatoxins or the negative health impacts from consuming contaminated products. Results reported in this paper show that aflatoxin contaminated staple crops are widely distributed in Tanzania and that the risk of human exposure is high due to diet preferences. Awareness campaigns are required to inform and protect farmers and consumers

Illustrations and guidelines for selecting statistical methods for quantifying spatial pattern in ecological data

This paper aims to provide guidance to ecologists with limited experience in spatial analysis to help in their choice of techniques, It uses examples to compare methods of spatial analysis for ecological field data. A taxonomy of different data types is presented, including point- and area-referenced data, with and without attributes. Spatially and non-spatially explicit data are distinguished. The effects of sampling and other transformations that convert one data type to another are discussed; the possible loss of spatial information is considered. Techniques for analyzing spatial pattern, developed in plant ecology, animal ecology, landscape ecology, geostatistics and applied statistics are reviewed briefly and their overlap in methodology and philosophy noted. The techniques are categorized according to their output and the inferences that may be drawn from them, in a discursive style without formulae. Methods are compared for four case studies with field data covering a range of types. These are: 1) percentage cover of three shrubs along a line transect 2) locations and volume of a desert plant in a I ha area: 3) a remotely-sensed spectral index and elevation from 10(5) km(2) of a mountainous region; and 4) land cover from three rangeland types within 800 km2 of a coastal region. Initial approaches utilize mapping, frequency distributions and variance-mean indices. Analysis techniques we compare include: local quadrat variance, block, quadrat variance, correlograms, variograms, angular correlation, directional variograms, wavelets, SADIE, nearest neighbour methods, Ripley's L(t), and various landscape ecology metrics. Our advice to ecologists is to use simple visualization techniques for initial analysis, and subsequently to select methods that are appropriate for the data type and that answer their specific questions of interest, It is usually prudent to employ several different techniques

Analyses of on-farm and augmented trials with mixed model ANOVA

Mixed Model procedure is used in the modeling and estimation of treatment efforts and variance components. It extends the generalized linear model (ordinary ANOVA) by avoiding the restrictive assumption of the error terms in ANOVA through the incorporation of the variance-covariance structure of all random terms. The mixed model procedure uses generalized least squares rather than the ordinary least squares, and estimates from mixed procedure are always better than those from the generalized linear model. The implementation of mixed model in SAS provides a powerful and flexible tool for analysing a wide range of data, including - the analysis of repeated measures, the analysis of spatially correlated data, the analysis of non-orthogonal designed experiments, and analysis of multilevel or hierarchical data (e.g. as in. on-farm trials). This paper looks at the two most important designs used in on-farm trials, 1) nested (hierarchical) design, and 2) augmented block design, and presents SAS programs useful for analysing data resulting from these designs