Occurrence and distribution of damping-off in Vigna subterranea in Benin and identification of associated causal agents

Bambara groundnut (Vigna subterranea (L.) Verdc.), also called ground peas or Bambara groundnut, is a West African seed legume of the Fabaceae family, playing an important social and economic role. The objective of the current study was to determine the occurrence, distribution and incidence of this disease on Bambara groundnut in agroecological production zones in Benin and to identify the causal agents responsible for the damages caused to the crop. A survey was conducted from 2019 to 2020 in five agroecological zones (AEZs) of Benin (AEZ2, AEZ3, AEZ4, AEZ5 and AEZ6). A total of 30 fields of Bambara groundnut were surveyed from 10 municipalities located in the agroeclogical zones of production at the early vegetative stage of the crop. Fields’ size of 0.5 ha were selected and scouted alongside both diagonals to evaluate the damping-off disease incidence. The results showed that damping-off occurred in four out of the five AEZs surveyed. The incidence rates varied from 0.00 to 23.33% in the AEZs 5 and 6 in 2019, and from 0.00 to 18.33% in the AEZ 6 in 2020. The highest incidence rates were obtained in the West Zone of Atacora (AEZ 4) and in the Food crop region of South (AEZ 3). Results of the correlation test showed a relationship between incidence, distribution of damping-off and climatic factors. However, most of regression equations showed a strong relationship between chemical properties of soils and incidence of damping-off. Sclerotium rolfssi was identified in the laboratory as the causal agent of the damping-off disease and isolated from diseased plants in the fields and during greenhouse pathogenicity tests. To the best of our knowledge, this is the first report of identification of pathogenic fungus as the causal agent of damping-off on Bambara groundnut seedlings in Benin. &nbsp

Contribution of seven legumes residues incorporated into soil and NP fertilizer to maize yield, nitrogen use efficiency and harvest index in degraded soil in the center of Benin

A field experiment evaluated the impact of seven legumes cover crops residues incorporated into degraded soil (Aeschynomene histrix, Centrosema pubescens, Chamaecrista rotundifolia, Mucuna pruriens, Pueraria phaseoloides, Stylosanthes guianensis and S. Hamata) on maize yield, N uptake and harvest index in the center of Benin. In July 2003, the cover crops were planted and received two level of phosphorus (45 P and 0 P) applied in form of Super Phosphate Triple. In May 2004, two split of nitrogen were added on the residues of the legumes, 30 days after the planting of maize. Minerals fertilizers (N, P) enhanced maize yield, N uptake, harvest index and N use efficiency. Incorporation of legumes residues improved more maize productivity than minerals fertilizers. The best grain yield (1793.9 kg DM.ha-1) and grain N uptake (149.4 kg N ha-1) were obtained with Mucuna pruriens residues incorporated. The combination of N and P to the different residues didn't improve significantly the maize yields. The maize grain yield is explained to 90% by biomass, harvest index and nitrogen use efficiency. The proportion of explained grain N uptake in biomass, harvest index and nitrogen use efficiency is 74%. The results demonstrated that growing maize with Mucuna pruriens residue incorporation with NP fertilizers could be more beneficial in the legume-maize cropping system in the study area.  Keywords: Crop residues, mineral fertilizers, maize yield, NUE, degraded soi

Effet des pratiques de conservation du sol sur la croissance et les composantes du rendement du mais dans le bassin versant de Lokogba au Benin

Les pratiques d’une agriculture de conservation visant une couverture permanente du sol suivie de la réduction du travail du sol pourrait être une innovation dans les stratégies paysannes pour une agriculture durable. La présente étude a pour objectif d’évaluer l’effet du mode de travail du sol et du mulching sur les performances agronomiques du maïs semé sur le bassin versant de Lokogba, à Aplahoué. Un essai en Bloc Complètement Randomisé à quatre répétitions et 8 traitements (Semis direct, Minimum labour, Labour à plat, Billonnage, Semis direct + Mulch en surface, Minimum labour + Mulch en surface, Labour à plat + Mulch en surface, Billonnage + Mulch surface) a été installé. Les résultats indiquent que le travail du sol a affecté significativement les performances agronomiques du maïs au seuil de 5 %. Le semis direct a enregistré les valeurs les plus faibles des paramètres (2,66 cm/j de vitesse de croissance, 65,81 cm2 d’indice foliaire, 797,8 kg MS/ha de grains et 911,8 kg MS/ha de pailles de maïs) contre le billonnage qui a enregistré les meilleures performances (3,62 cm/j de vitesse de croissance, 120 cm2 d’indice foliaire, 2175,4 kg MS/ha de grains et 2475,4 kg MS/ha de pailles de maïs). L’indice de récolte et le diamètre au collet des plants les plus élevés 0,4 % et 1,37 cm, respectivement, ont été obtenus avec le labour à plat. Le mulching a amélioré le diamètre au collet des plants de 1,28 à 1,37 cm, l’indice foliaire de 73,05 à 114,02 cm2 (p < 0,0001) et la vitesse de croissance des plants de 2,91 à 3,75 cm/j (p < 0,0001). Le rendement en grains est passé de 1020,5 kg MS/ha sans couverture de mulch à 2138,1 kg MS/ha avec couverture de mulch et l’indice de récolte de 31,1 à 41,1 p.c. La combinaison des deux facteurs n’a toujours pas donné un effet significatif sur les performances agronomiques du maïs. Quels que soient le mode de travail du sol et la couverture ou non de mulch, le rendement en grains dépend significativement de l’indice de récolte, des spathes et des pailles du maïs (100r2 = 95,34).Mots clés: Semis direct, labour, mulching, maïs, bassin versantEnglish Title: Effect of soil conservation practices on maize productivity in Lokogba watershed in BeninEnglish AbstractConservation agriculture with permanent soil covering could be an innovation in farming practices dealing to sustainable agriculture. This study aims to evaluate the effect of tillage and mulching on the agronomic performance of maize, planted in the watershed of Lokogba in Aplahoué. A randomized completed bloc design with four replications was chosen. Eight treatments were concerned in the trial as followed: Direct sowing, Minimum tillage, Tillage, Conventional tillage, Direct sowing + Mulch on surface, Minimum tillage + Mulch on surface, Tillage + Mulch on surface, Conventional tillage + Mulch on surface. Results indicated that tillage significantly affected the agronomic performance of maize. Direct seeding recorded the lowest parameters (2.66 cm.day-1 of growth rate and 65.81 cm2 of leaf area index, 797.8 kg DM.ha-1 of grain and 911.8 kg DM.ha-1 of maize straw) against conventional tillage with the best performance (3.62 cm.day-1 of growth rate and 120 cm2 of leaf area index, 2175.4 kg DM.ha-1 of grain and 2475.4 kg DM.ha-1 of maize straw). The  highest harvest index and collar diameter of plants (0.4% and 1.37 cm, respectively) were obtained with the tillage. Mulching improved the collar diameter of plants from 1.28 to 1.37 cm (but no significantly), the leaf area index from 73.05 to 114.02 cm2 (p < 0.0001) and the growth rate from 2.91 to 3.75 cm.day-1 (p < 0.0001). The grain yield increased from 1020.5 kg DM.ha-1 without mulch to 2138.1 kg DM.ha-1 with mulch and harvest index from 31.1 to 41.1 %. The combination of both factors have not a significant effect on the agronomic performance of maize. Whatever the type of tillage and with or without mulch, the grain yield significantly depends on the harvest index, husk and maize straw (100r2 = 95.34).Keywords: Direct seeding, tillage, mulching, maize, watershe

Réponse à l’inoculation mycorhizienne de quatre variétés de niébé [Vigna unguiculata (L.) Walp.] cultivées au Burkina Faso et au Sénégal

La culture du Niébé [Vigna unguiculata (L.) Walp.] en Afrique de l’Ouest est marquée par l’instabilité de ses rendements et sa faible production liée à la pauvreté des sols, à la faiblesse de la pluviométrie et aux contraintes parasitaires. Dans cette étude, nous nous sommes intéressés à la réponse à l’inoculation mycorhizienne de quatre variétés de niébé dans une perspective de sélection de souches efficaces de champignons endomycorhiziens pour l’amélioration de sa productivité au champ. Quatre variétés de niébé dont deux du Burkina Faso [Gorom Local (GO) et KVX 396-4-5-2D (KVX)] et deux du Sénégal [Mélakh (Mel) et Yacine (Yac)] ont été inoculées en pépinière avec trois (3) inoculums mixtes du Burkina Faso [Yakouta (Ya), Talé Mossi (Ta) et Soumousso (Sou)] et trois inoculums monospécifiques de la collection du Laboratoire Commun de Microbiologie de Dakar (LCM) [Glomus mossea (Gm), Glomus fasciculatum (Gf) et Glomus intraradices (Gi)]. Les effets des différents inoculums sur la croissance des plants ont été évalués par la mesure de la hauteur des plants, des biomasses aérienne et racinaire et de la fréquence et intensité de mycorhization à la floraison et à la fructification. Les résultats obtenus montrent que l’inoculation n’a pas eu d’effets significatifs sur les différents paramètres mesurés pour les variétés du Sénégal malgré des taux demycorhization de 6% à 92% à la floraison et de 44% à 100% à la fructification. Pour les variétés du Burkina Faso, à la floraison, la croissance en hauteur et la production de biomasse aérienne de la variété KVX ont été améliorées par toutes les souches, exceptée Gm. Pour la variété GO, les inoculums mixtes indigènes Ya et Ta ont significativement amélioré la croissance en hauteur des plants. En général, les fréquences et les intensités de mycorhization sont élevées pour les souches monospécifiques, mais ceci ne se traduit pas par un effet significatif sur la croissance des plants inoculés. L’inoculum mixte indigène Ya apparaît plus performant pour la croissance en hauteur et la production de biomasse de la variété la plus sensible à l’inoculation (KVX). Cette étude a montré que l’inoculation endomycorhizienne a un effet bénéfique sur la croissance du Niébé, particulièrement la variété KVX ; et que l’utilisation de souches indigènes conviendrait mieux que les souches monospécifiques. Il s’avère donc intéressant de poursuivre la sélection de souches performantes pour la productivité du Niébé sur les souches indigènes.Mots clés: champignons mycorhiziens, croissance du Niébé, pépinière, Afrique de l’Oues

Biogeographical survey of soil microbiomes across sub-Saharan Africa:structure, drivers, and predicted climate-driven changes

BACKGROUND: Top-soil microbiomes make a vital contribution to the Earth’s ecology and harbor an extraordinarily high biodiversity. They are also key players in many ecosystem services, particularly in arid regions of the globe such as the African continent. While several recent studies have documented patterns in global soil microbial ecology, these are largely biased towards widely studied regions and rely on models to interpolate the microbial diversity of other regions where there is low data coverage. This is the case for sub-Saharan Africa, where the number of regional microbial studies is very low in comparison to other continents. RESULTS: The aim of this study was to conduct an extensive biogeographical survey of sub-Saharan Africa’s top-soil microbiomes, with a specific focus on investigating the environmental drivers of microbial ecology across the region. In this study, we sampled 810 sample sites across 9 sub-Saharan African countries and used taxonomic barcoding to profile the microbial ecology of these regions. Our results showed that the sub-Saharan nations included in the study harbor qualitatively distinguishable soil microbiomes. In addition, using soil chemistry and climatic data extracted from the same sites, we demonstrated that the top-soil microbiome is shaped by a broad range of environmental factors, most notably pH, precipitation, and temperature. Through the use of structural equation modeling, we also developed a model to predict how soil microbial biodiversity in sub-Saharan Africa might be affected by future climate change scenarios. This model predicted that the soil microbial biodiversity of countries such as Kenya will be negatively affected by increased temperatures and decreased precipitation, while the fungal biodiversity of Benin will benefit from the increase in annual precipitation. CONCLUSION: This study represents the most extensive biogeographical survey of sub-Saharan top-soil microbiomes to date. Importantly, this study has allowed us to identify countries in sub-Saharan Africa that might be particularly vulnerable to losses in soil microbial ecology and productivity due to climate change. Considering the reliance of many economies in the region on rain-fed agriculture, this study provides crucial information to support conservation efforts in the countries that will be most heavily impacted by climate change. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s40168-022-01297-w

Relation symbiotique entre Mucuna et Rhizobium, département du Mono au Bénin

Dans IDL-1387

Crop rotation based grain legumes as a soil fertility management strategy in lowland rice-based cropping systems in centre of Benin

peer reviewe

Effect of bradyrhizobial inoculation and n fertilization on promiscuous soybean and subsequent maize yield grown in degraded “terre de barre” in Benin

Poor adoption of green manure and agro forestry systems for sustainable intensification of agricultural production in the moist savannah of West-Africa, as well as the low contribution of traditional grain legumes such as groundnuts, cowpea and common bean have prompted the search for alternative socio-economic solutions for smallholders. One of them is the development of N2 fixation by promiscuous soybean to increase food production and to improve soil fertility, in particular on degraded lands. Fifteen farmers’ fields were selected for soybean trials in 2001 and 2002, and again in 2002 and 2003 for the maize trials. Each farmer’s field represented one replication. The 15N isotope dilution method was used to assess symbiotic N2 fixation of the International Institute for Tropical Agriculture (IITA) promiscuous soybean variety TGX 1448 2E and its response to inoculation and fertilization. In both 2001 and 2002, the application of 20 kg N did not affect nodulation, biomass production and N accumulation of soybean uninoculated in 2001, or inoculated in 2002. However, inoculation produced the highest soybean nodule number and nodule weight in 2002. The highest values of biomass production and N accumulation were found with soybean that received poultry manure in 2001 and 100 kg N ha-1 as urea in 2002. The highest biomass and N accumulation in 2001 was 1600 kg DM ha-1 and 41 kg N ha-1 with soybean amended with poultry manure. Shoot N content in 2002 averaged only 25 kg N ha- 1, while the average N accumulation in soybean seed was 64 kg N ha-1. The best percentage of N derived from atmosphere (Ndfa) (54 %), amounting to only 13 kg N ha-1, was obtained with soybean fertilized with 20 kg N ha-1 and inoculated. These values are very low indicating that soybean cultivated in the study area was far from satisfying its requirements through N fixation. The N balance calculated on the basis of the amount of N fixed removed in the grain is negative (-48 kg ha-1). Significant increase occurred only when plots were previously grown to soybean and fertilized with poultry manure being 5124 and 3211 kg DM ha-1 compared to the previous soybean plot without N, for maize shoot and grain, respectively. Total N yield in shoots was significantly higher in plots previously cropped to soybean than to maize. The contribution of soybean to maize yield was not significantly different from the contribution of maize-to-maize in 2003. Soybean growing in West-Africa is a promising technology that has multiple benefits.Keys words : Benin Republic ; promiscuous soybean ; symbiotic N fixation ; 15N isotope dilution; N accumulation ; N Balance ; % Ndfa