Opportunités et contraintes agroforestières de Ricinodendron heudelotii au Cameroun

Ricinodendron heudelotii est une essence endémique des forêts tropicales humides d’Afrique, très prisée pour ses graines comestibles. Sa régénération naturelle reste difficile à cause principalement de la dormance tégumentaire de ses graines. Elle possède de nombreuses vertus ethnobotaniques et d’opportunités agroforestières pour les peuples des forêts du bassin du Congo. Au nombre de ces vertus, on cite des propriétés médicinales, agroalimentaires, agronomiques, écologiques et industrielles. Des programmes de domestication de R. heudelotii sont en cours dans les stations du Centre Mondial de l’Agroforesterie (CMAF) au Cameroun. L’essentiel des travaux déjà réalisés sur cette essence a porté sur ses propriétés ethnobotaniques, l’analyse de la composition chimique de l’huile des graines et sa domestication. Les tentatives de domestication de R. heudelotii se heurtent par ailleurs à diverses contraintes phytosanitaires encore à identifier. Sur la base des observations réalisées en forêts, dans les pépinières et au laboratoire, les dégâts observés seraient d’origine fongique et entomologique. À ce jour, aucun programme de lutte ou d’amélioration génétique n’est envisagé. Pourtant, l’existence de deux sous-espèces (heudelotii et africanum) chez R. heudelotii et d’une espèce apparentée (R. rautanenii) constitue un atout exploitable pour d’éventuels travaux d’amélioration génétique. Cette étude suggère que R. heudelotii pourrait être considérée comme une essence modèle d’avenir pour l’agroforesterie au Cameroun, avec au premier plan un moyen de lutte prometteur contre la pauvreté, et propose quelques pistes de recherche en vue de contribuer au succès des programmes de  domestication de l’espèce. © 2013 International Formulae Group. All rights reserved.Mots clés : Ricinodendron heudelotii, intérêt agroécologique, contraintes agroforestières, amélioration génétique

Impact of fungicide applications for late blight management on huckleberry yields in Cameroon

The influence of late blight infections, caused by Phytophthora infestans, was evaluated on thirteen huckleberry (Solanum scabrum) varieties during the 2000 and 2001 cropping seasons in Dschang, Cameroon. A randomised split block design was used. Plants were sprayed four times with Ridomil Plus® (12% metalaxyl + 60% cuprous oxide) at 2.5 kg ha-1 on a 21-day schedule while control plots were not sprayed. Late blight intensity was recorded weekly and fresh shoot yields were evaluated six times at 14-day intervals. Fungicide applications significantly reduced late blight intensity and consequently increased huckleberry yields. Cumulative shoot yields varied with the variety and fungicide treatment, from 54.14 to 238.33 t ha-1. Yield losses due to late blight infection were estimated at up to 46%. Economic analyses indicated that fungicide sprays are necessary for a late blight protection programme in huckleberry. This spray regime based on fungicide application resulted in net profits of US$694 to$ 8,467 ha-1, depending on the variety used and the trial period. The results show that late blight infections if not controlled, decrease huckleberry yields, and consequently net farm incomes. High yielding resistant varieties or foliar applications of Ridomil Plus® may be incorporated in integrated pathogen management schemes against late blight in huckleberries with a view to minimise use of fungicides. Key Words: Integrated management, Phytophthora infestans, Solanum scabrum, yield loss Résumé L'influence du mildiou, causé par Phytophthora infestans, était évalué sur treize variétés de la morelle noire (Solanum scabrum) pendant les saisons culturalles de l'an 2000 et 2001 à Dschang, Cameroun. Les éssais étaient réalisés en split-blocs pris au hazard. Les plantes étaient traitées quatre fois avec Ridomil Plus (12% de métalaxyl + 60% oxyde cuivreux) à 21 jours d'intervalle à la dose de 2.5 kg ha-1. L'intensité du mildiou a été évalué hebdomadairement et les pousses fraiches ont été récoltées six fois à l'intervalle de 14 jours. Des traitements fongicides ont significativement réduit l'intensité du mildiou et par conséquent augmenté le rendement en pousses. Le rendement total en pousses fraiches a été variable. De 54, 14 à 238,33 t ha-1, selon la variété et le traitement fongicide. Des pertes en rendements associées aux attaques du mildiou ont atteint 46%. Des analyses économiques indiquent que quatre traitements au Ridomil plus"sont nécessaires dans un bon programme de protection de la morelle noire contre le mildiou. Ce régime de traitement a poduit des augmentations en revenu net de USS 694 à 8.467 ha-1, selon la variété utilisée et la période d'essai. Des résultats indiquent que le mildiou peut baisser le rendement de la morelle noire et par conséquent le bénéfice net des planteurs de la morelle noire si les actions appropriées ne sont pas menées pour rayer les effets néfastes de cette maladie. En outre, l'utilisation des variétés résistantes ou des traitements foliaires au Ridomil plus" peut etre incorporée dans des programmes de lutte intégrée contre le mildiou de la morelle noire. Mots Clés: Gestion intégrée, Phytophthora infestans, Solanum scabrum, perte de rendement (Af Crop Sci J 2003 Vol 11 No 3 pp163-170

Effect of Compost Quality and Microbial Population Density of Composts on the Suppressiveness of Pythium myriotylum, Causal Agent of Cocoyam (Xanthosoma sagittifolium) Root Rot Disease in Cameroon

The effect of eight compost types made from four different grass species mixed with poultry and pig manure and microbial population in compost were evaluated on the suppressiveness of the root rot disease on cocoyam. The experimental layout was a complete randomized design with five replicates conducted in a screen house in the Faculty of Agronomy and Agricultural Sciences, University of Dschang. Compost was used in the ratio of 1:1 by weight (2kg compost: 2kg soil/plant). It was inoculated 48 hours before planting to enable compost-pathogen interaction. Compost microbial populations were estimated using dilution plating with appropriate media (tryptic soil agar, TSA) for Heterotrophic bacteria and Actinomycetes isolation agar for Actinomycetes respectively. The physicochemical properties (pH-H2O, CEC, N, K, Na, Mg and Ca) of compost were determined and analysed. Disease incidence and severity was significantly (

Bioassay of Geniculosporium species for Phytophthora megakarya biological control on cacao pod husk pieces

Fungal endophytes (Geniculosporium sp.) isolated from cacao leaves were screened for biological control of Phytophthora megakarya the cacao black pod disease pathogen, using Cacao Pod Husk Pieces (CPHP). CPHP were pre-treated with spore suspensions of Geniculosporium sp. [BC13 (GJS 01- 196), BC108 (GJS 01-192), BC118 (GJS 01-197), BC177 (GJS 01-198)], and were infected with P. megakarya zoospore suspensions (105 zoospores/ml). Effects on P. megakarya were noticed at pod infection, mycelia growth inside infected tissues, and fungal sporulation, that are major stages of the black pod disease cycle on cacao pods. CPHP pre-treated with BC108 expressed the lowest early Infection Index (EII), but could not control disease progress into infected cacao pod husk tissues. On CPHP pre-treated with BC13, average growth rate of the necrosis was significantly reduced, but no control on P. megakarya sporulation was observed, while CPHP pre-treated with BC177 significantly reduced P. megakarya sporulation.Key words: Cacao, biological control, Geniculosporium sp, endophytes, Phytophthora megakarya, pod husks pieces

Influence of rate and frequency of Ridomil plus applications on late blight severity and potato yields in Cameroon

The impact of Ridomil Plus® (12% metalaxyl + 60% cuprous oxide) spray rate and frequency on the severity of potato late blight, caused by Phytophthora infestans, was evaluated during 1997 and 1999 in Dschang, Cameroon. A randomised complete block design was used in both experiments. In 1997, plots were sprayed with 0.6, 1.2, 2.4, or 4.8 kg a.i.ha-1 of Ridomil Plus®, while in 1999, they were treated once, twice or thrice with 2.4 kg a.i.ha-1 of the fungicide. In both trials control plots were not sprayed. Late blight intensity was recorded weekly and yields were obtained at harvest. Fungicide applications reduced late blight intensity and consequently increased potato tuber yields. Marketable yields were significantly higher in the resistant variety, Cipira (22.4 - 34.8 t ha-1), than in the susceptible variety, Tezelfeu (4.0 - 12.0 t ha-1). A significant quadratic relationship existed between the rate or number of fungicide applications and tuber yields. Economic analyses indicated that two sprays of the fungicide at 2.4 kg a.i. ha-1 are necessary for a good late blight protection programme in potato. This spray regime resulted to increases in net returns of US$ 1947 to 3327 ha-1. Results also suggest that high rates or frequencies of fungicide applications do not necessarily lead to better economic benefits. Key Words: Economic gains, fungicide application, Phytophthora infestans, Solanum tuberosum (African Crop Science Journal 2001 9(1): 235-244

Efficacy of herbicide formulations for weed control in maize in a humid tropical environment

Weeds are a serious constraint to maize production in the tropics. A field experiment was conducted in Cameroon, at the University of Buea Research farm in 2009 and 2010 to evaluate the efficacy of formulations of nicosulfuron (Nicomaïs 40SC), glyphosate (Roundup 360) and paraquat (Gramoxone 200g a.i./l) for weed control in maize. Treatments were nicosulfuron applied at 1 l/ha two weeks after planting maize, glyphosate applied at 6 l/ha before planting maize, paraquat applied at 6 l/ha with hoe weeded and unweeded control plots. Results showed that in both years, the weeded control and all herbicide treatments had lower weed density and dry matter, and higher grain yield than the unweeded control. The unweeded control had 1.3- 3.2 times more weeds than the herbicide treatments at crop harvest. Treatments with nicosulfuron gave the highest reduction in weed dry matter (92%). Treatments with glyphosate reduced weed dry matter by 59%, while those with paraquat gave a reduction of 49%. Maize grain yield in nicosulfuron treatments and the weeded control was similar and higher than that in treatments with glyphosate by 26%, those with paraquat by 51% and the unweeded control by 61%. The net gain of treatments with nicosulfuron was more than that with all other treatments. Nicosulfuron was more effective for weed control in maize than glyphosate and paraquat because it provided seasonal long control of the dominant weed species

The potential of kyllinga erecta Schumach and Cyperus rotundus Linn. to remediate soil contaminated with heavy metals from used engine oil in Cameroon

Contaminated soils are a serious environmental problem in developing countries. Poor disposal of used engine oil from vehicles is a source of soil contamination in Buea, Cameroon. This study was conducted in the University of Buea Teaching and Research Farm to determine the ability of two sedges (Kyllinga erecta Schumach and Cyperus rotundus Linn.) to remediate crop land contaminated with used engine oil. The experiment consisted of the two sedges and the following used oil levels (v/wt): 0, 5, 10, 20, 40 and 60 ml/kg of soil. Control treatments with 0 and 60 ml of used engine oil/kg of soil without the sedges were also included. The plant (roots and shoots) and soil samples were analyzed for heavy metal contents using the Inductively Coupled Plasma Optical Mass Spectrometry analytical package for ultra-low detection and high precision. The root and shoot dry biomass of both sedges decreased with an increase in soil contamination. Cyperus rotundus accumulated high concentrations of Cr (mean = 64.8 ± 19.5 ppm) and Cd (mean =1.2 ± 0.2 ppm) in its roots. Kyllinga erecta had the potential to extract Sn, Cd, Mn, Sr and Mo on soils contaminated with used oil at 60 ml/kg. Cyperus rotundus had phytostabilisation potential for Cd at concentrations of used oil ≤20 ml/kg and Rb at 20 ml/kg. The sedge also had phytoextraction potential for Cr and Rb on soils contaminated with used oil at concentrations up to 20 ml/kg. Therefore, the use of indigenous plants adapted to tropical environments could be a possible option for the sustainable remediation of soils contaminated with heavy metals from used engine oil

Seed coating herbicide tolerant maize hybrids with imazapyr for Striga hermonthica (Del.) Benth control in the West African savanna

Striga hermonthica is a serious threat to cereal production in the savannas of sub-Saharan Africa. Field trials were conducted in Nigeria at Abuja and Mokwa (southern Guinea savanna) in 2005 and 2006, and at Zaria (northern Guinea savanna) and Sabongari (Sudan savanna) in 2006, to evaluate the performance of imazapyr coated maize hybrids with the herbicide resistance (IR) gene under Striga infestation. Treatments were seven IR maize hybrids, and three checks without the IR gene (the commercial hybrid Oba Super 1, a Striga tolerant line 9022-13, and a Striga susceptible line 8338-1). The hybrids were either coated with imazapyr and sown under Striga infestation or uncoated and sown in Striga-free conditions. Across all locations, six of the IR maize hybrids were high-yielding under Striga infestation. Seed coating significantly reduced Striga emergence and damage to the maize plants at all locations. The Striga susceptible hybrid check, 8338-1, had a high level of Striga damage and sustained a yield loss of 99% when uncoated and sown under Striga infested conditions. In Striga-free plots, the checks had yields comparable to that of the seven IR maize hybrids. Significant negative correlations were detected between grain yield and Striga damage ratings (rp = -0.64) at Abuja and Mokwa. The findings indicate that seed coating IR maize hybrids with imazapyr was effective for Striga hermonthica control

Response of weeds and soil microorganisms to imazaquin and pendimethalin in cowpea and soybean

Published online 23 August 2014Herbicides applied to combat weeds and increase crop yields may also have undesired effects on beneficial soil microorganisms. Field studies were conducted in 2005 and 2006 in Zaria, Nigeria, to evaluate the response of weeds and soil microorganisms to imazaquin applied at 0.05, 0.10, 0.20 and 0.40 kg a.i./ha and pendimethalin applied at 1.0, 2.0, 4.0, and 8.0 kg a.i./ha in cowpea and soybean. Hoeweeded and unweeded (no herbicide) plots were controls. Both herbicides significantly reduced weed biomass in both crops, when compared to the unweeded control, which had the highest weed biomass at all sampling dates. Treatments with 0.40 kg a.i./ha of imazaquin, 2.0 and 4.0 kg a.i./ha of pendimethalin, and the hoe-weeded control, had the highest cowpea grain yield. The unweeded control had the lowest grain yield which was comparable to that in all other herbicide treatments. All treatments except 4.0 and 8.0 kg a.i./ha of pendimethalin had higher soybean grain yield than the unweeded control. Soybean yield was lowest in the unweeded control, and treatments that received 4.0 and 8.0 kg a.i./ha of pendimethalin. All rates of imazaquin gave similar soybean grain yields that were 29e41% higher than that from pendimethalin. The hoe-weeded control had the highest yield, which was 79% more than that in the unweeded control. Higher rates of imazaquin and pendimethalin reduced nodulation, nitrogen fixation, and vesicular arbuscular mycorrhizal (VAM) fungi colonisation in both crops. VAM fungi species diversity and species richness in cowpea rhizosphere soil and species diversity in soybean rhizosphere soil were reduced relative to the controls due to application of both herbicides with the rates of 0.10, 0.20, and 0.40 kg a.i./ha of imazaquin and 8.0 kg a.i./ha of pendimethalin being significantly effective