Amougou Akoa

Influence of phosphorus application and arbuscular mycorrhizal inoculation on growth, foliar nitrogen mobilization, and phosphorus partitioning in cowpea plants

The present study was undertaken to evaluate the effects of phosphorus (P) application and arbuscular mycorrhizal (AM) fungi (Funneliformis mosseae) on growth, foliar nitrogen mobilization, and phosphorus partitioning in cowpea (Vigna unguiculata cv. Vita-5) plants. The experiment was conducted in a greenhouse in pots containing a mixture of vermiculite and sterilized quartz sand. Mycorrhizal and non-mycorrhizal cowpea plants were supplied with three levels of soluble P (0.1 (low P), 0.5 (medium P), or 1.0xa0mM (high P)).Cowpea plants supplied with low P fertilization showed significantly (pu2009<u20090.05) higher root colonization than those with medium and high P fertilization at both the vegetative and pod-filling stages. P uptake and growth parameters of cowpea plants were positively influenced by mycorrhizal inoculation only in the medium P fertilization treatment at the vegetative stage. Lack of these effects in the other treatments may be linked to either a very low P supply (in the low P treatment at the vegetative stage) or the availability of optimal levels of freely diffusible P in the substrate towards the pod-filling stage due to accumulation with time. The N concentration in leaves of all cowpea plants were lower at the pod-filling stage than at the vegetative stage, presumably as a result of N mobilization from vegetative organs to the developing pods. This was however not influenced by AM fungal inoculation and may be a consequence of the lack of an improved plant P acquisition by the fungus at the pod-filling stage.

Artificial infestations of Tapinanthus ogowensis (Engler) Danser ( Loranthaceae ) on three host species in the Logbessou Plateau (Douala, Cameroon)

In Cameroon today, Loranthaceae has become a major pest against which a great “battle” must be launched if food production in the country has to be maintained at a self-sufficient level. However, an effective battle against pests can only be achieved through a better understanding of their geographical distribution and biology. Eight Loranthaceae species (Globimetula braunii, Globimetula dinklagei, Globimetula opaca, Helixanthera mannii, Phragmanthera capitata, Tapinanthus globiferus, Tapinanthus ogowensis, and Tapinanthus preussii) have been identified in the Douala area. Among these species, T. ogowensis is the only one limited to a surface area of about eight hectares in the Logbessou plateau located in a direction of North-East from Douala (Latitude 03°40 - 04°11 N, Longitude 09°16 - 09°52 E, and at an altitude of 13 m). In this zone, the hemi-parasite infests only one host tree (Dacryodes edulis) in the orchards, gardens and agricultural plantations. The hemiparasite is however common and adapted to all the different ecological regions in the southern part Cameroon where it infests several host trees. In order to study the stages involved in the germination, fixation, as well as the initial stages involved in the development of the seedlings of T. ogowensis, three of the most frequent host species (D. edulis, Mangifera indica and Persea americana) on the plateau were artificially infected. The results revealed that the host species are sensitive to the parasite, T. ogowensis, at least during their early stages of growth and development. D. edulis is the most sensitive host species with a 22% yield of young seedlings as against 5 and 4% for P. americana and M. indica, respectively. This sensitivity of the mango tree to T. ogowensis had never been demonstrated before. The percentages of seeds germinating on the different host species however remained high; 96% on both D. edulis and M. indica and 93% on P. americana. It was also revealed that the development of the young seedlings of T. ogowensis is greatly influenced by the availability of light, a plausible reason why Loranthaceae occupies mainly the uppermost branches of the oldest trees found here.

Biodiversity Conservation and Carbon Sequestration in Cocoa Agroforest in Southern Cameroon

The study is conducted in semi deciduous rain forest zone of southern Cameroon to appreciate the impact of cocoa agroforest on plant biodiversity conservation and carbon sequestration. Twenty-four transects of 1.5 km long and 10 m wide were established in eight villages to evaluate the cover percentage of cocoa compare to other land use system (LUS). Forty five plots of 625 m2 (25 m x 25 m) each were surveyed in these villages. In these plots, all the individuals with DBH (Diameter at the Breast Height) greater or equal to 4 cm were recorded. The destructive method was used to evaluate carbon sequestration in different LUS for herbaceous plants, small woody plants, litter and roots, while the allometric equation of Brown was used for all individuals with DBH ≥ 4 cm. Seven LUS were identified in the Yaounde region: 23 % of these were cultivated land, 36 % were fallows, 16 % were cocoa field and 5 % represented the secondary forest derived from the slash and burn practices. In the regions of Mbalmayo and Ebolowa, eight LUS were identified, of which six shared with the region of Yaounde and two different, the degraded forest and swampy forest. Species encountered in cocoa agroforest represent 33.78 % of the total flora of the area. Fruit trees were abundant in those villages which have access to market (Persea americana, Dacryodes edulis, Citrus spp), while in Ambam region, original forest species mostly timber species were encountered (Baillonella toxisperma, Guibourtia tessmannii, Terminalia superba, Milicia excels). This agroforest can accumulate about 251.14 t C/ha. Theobroma cacao hosted about 21.51 t C/ha. The root system of cover species stocks an important quantity of carbon.

Climatic niche of #Dacryodes edulis# (G. Don) H.J. Lam (Burseraceae), a semi-domesticated fruit tree native to Central Africa

Dacryodes edulis is a fruit tree growing naturally in the rainforests of Central Africa. To provide data to scientists and forest managers for the habitat of D. edulis in the wild, the study of ecological niche and environmental adaptation was carried out. The geographical coordinates of 168 collections of wild individuals and 19 climatic parameters were treatedunder Geographical Information System. Potential spatial richness, favourable climatic parameters and elevation of the species were described. The favourable climatic conditionsfor natural growth of D. edulis were mainly revealed in the forests of Gabon and Equatorial Guinea. In Cameroon, these conditions were well marked in the regions of Kribi and Bipindi(South), in the forest of Yingui and Yabassi (Littoral), in the Dja Forest (East) and South-West towards the border with Nigeria. The mean of favourable annual precipitation is 2205.26 ± 505.5 mm per year. The optimal annual mean temperatures stretch from 23.5 to 25.5°C. The favourable elevations stretch from 0 to 800 m. These values are smaller than ones for domesticated individuals which represent fundamental climatic niche. Prospect inforest areas with the best favourable climatic conditions and elevation for natural growth ofD. edulis should be encouraged to ensure in situ conservation of wild populations for maintaining genetic diversity. (Resume dauteur)

Evaluation of the sensitivity of two plantain varieties essong and big ebanga to the nematode Radopholus similis

Plantains are among the crops that enhance food security in Cameroon. However, plantain yields remain low because of several constraints of parasites such as Radopholus similis , a nematode that can cause losses up to 75% in fields when no protection measures are taken. In most cases, the sensitivity of local plantain varieties to R. similis is unknown; which generally results to low yields despite the control technique used. This limits their up scaling in the country. This work was undertaken to study the sensitivity of two varieties, Essong and Big Ebanga, to R. similis . To this effect, the parasitic activity of R. similis on the varieties Essong and Big Ebanga was assessed in vivo. The variety Grande naine known to be very sensitive to R. similis was used as the control. According to the results obtained, local varieties Essong and Big Ebanga were found to be sensitive to R. similis with the variety Essong being the most sensitive. Key words : Musa spp ., banana plantain, nematode, Radopholus similis, sensitivity.