Introduction. A previous paper showed that Al in the nutrient solution affected the growth, biomass production and chemical composition of bananas (Musa spp.). This paper aims at providing complementary results on the effect of Al on water and nutrient uptake by young banana plants. Materials and methods. Vitroplants of five cultivars (Grande Naine, Agbagba, Obino l'Ewaï, Igitsiri and Kayinja) were grown for 40 d in a phytotron with a temperature close to that of their cropping areas. Dilute nutrient solutions without Al and with 78.5 μM Al were supplied continuously with peristaltic pumps. Measurements of daily water and nutrient uptake were carried out twice a week. Rhizosphere acidification or alcalinisation were also monitored. Results and discussion. Aluminium reduced plant water uptake and cumulative detrimental effects were observed. After 40 d, water uptake was only 30-40% of the control. Without Al, nutrient uptake (Ca, Mg, K, P, NO3-N, NH4-N) increased with time, whereas Al inhibited the uptake of all elements, particularly Mg. As for water absorption, cumulative effects were observed: after 40 d, most nutrient uptake rates were reduced by more than 50% relatively to the control. The plantain bananas, Agbagba and Obino l'Ewaï, were more resistant to Al than the others. Changes of temperature are likely to modify Al sensitivity as one cultivar, Kayinja, showed greater Al sensitivity at 28/25°C than at 24/20°C.

Introduction. To compare the mineral nutrition of organically and normally grown banana plants, observations were made on growth and yield of organic banana plants, at the Canary Islands. The data were then discussed opposite the results previously reported for conventional plantations. Materials and methods. Growth parameters (plant height, leaf emission rate, pseudostem circumference) and yield parameters (bunch weight, number of hands, finger grade, etc.) were measured during ten months on an organically grown banana plantation of Dwarf Cavendish cv. Leaf N, P, K, Ca, Mg, Cu, Fe, Mn and Zn contents were also assessed. Results and discussion. Leaf emission rates showed higher values in late spring and early summer (0.099-0.109 leaf$\cdot$d-1), while pseudostem circumference grew more in late spring (0.238 cm$\cdot$d-1) than in summer. In August, pseudostem circumference decreased dramatically, probably because the plants with a larger circumference had flowered before that month and could not be measured. Bunches gave good yields for the zone (43.59 kg on average) and had a high mean number of hands (12.79). Number of fingers of the second upper hand (25.63), their grade (37.63 cm), length (23.50 cm) and weight (165.19 g) ranged from normal to high. Month of harvesting influenced yield and quality of the fruits. Leaf content of N, P, Mg, Cu, Fe, Mn and Zn fell within the normal range related to the conventionally grown banana plants. Potassium foliar content showed low levels but not deficiencies, whereas Ca leaf concentrations were high but not excessive. No relationship was found among leaf nutrient levels and growth, yield and fruit quality parameters.

Introduction. The fruit of `Encore' mandarin (Citrus deliciosa × Citrus nobilis) usually shows chlorotic spots in the epicarp from the first stages of development. This peel disorder triggers off, thereafter, the occurrence of a large quantity of dark stains (pre-harvest `peel pitting'). Materials and methods. A biochemical and ultra-structural study of the flavedo, using epicarp with and without stains, was carried out. Quality assays were assessed on the edible portion of the fruit or on juice. Results. The cell structure of pitted and unpitted epicarp analysed by electron microscopy revealed that dark spots were associated with the degradation of cellular membranes. The peroxidase system that shields the epicarp against photooxidative stress showed an inhibition of catalase activity and an increase of superoxide dismutase functioning. Moreover, the activities of ascorbate peroxidase and glutathione reductase remained unaffected in stained tissues. In sunshade trees, it was also found that the number of dark stains per fruit decreased but the internal quality of the endocarp was not significantly affected. The weight and the caliber of the fruit also slightly decreased. Discussion. High light intensities induce an oxidative stress in the epicarp, which is characterized by an increased peroxidation and degradation of biological membranes. On the other hand, protection against solar radiation alleviates the stress, but, although not affecting the internal quality of the fruit, slightly decreases the fruit weight and size.

Introduction. La culture des agrumes est très répandue en Guinée sous forme de vergers de case. La moyenne Guinée (Fouta Djalon), principale région productrice d'oranges, assure environ les deux tiers de la production nationale et la presque totalité des exportations régionales. Cependant, à la fin de 1993, la cercosporiose due à Phaeoramularia angolensis a envahi les zones d'altitude du pays à partir de foyers primaires situés en moyenne Guinée, entraînant une nette diminution de la production. Matériel et méthodes. Trois enquêtes par région naturelle et par an ont été effectuées dans plusieurs localités du pays pour établir les limites d'extension de la maladie. Des échantillons de feuilles et de fruits suspects, prélevés sur 25 arbres par localité, ont été identifiés en laboratoire. La vitesse moyenne de progression de la maladie a été estimée. Résultats et discussion. Les observations faites en champ et complétées par les travaux de laboratoire entre 1995 et 1998 ont confirmé la présence de la maladie. Les zones agrumicoles situées à plus de 400 m d'altitude ont été particulièrement touchées par le fléau. Les zones basses et chaudes de la Guinée maritime et de la haute Guinée sont épargnées. La maladie progresserait à une vitesse de 23 km$\cdot$an-1. Conclusion. La cercosporiose des agrumes continue sa progression en Guinée. La presque totalité des vergers du Fouta Djalon est atteinte. La reconversion des zones agrumicoles touchées par la maladie devrait être envisagée par diversification fruitière et délocalisation des nouvelles plantations vers des zones basses et écologiquement protégées.

Introduction. Two field experiments were conducted to investigate the effects of potassium (K) on plant growth, fruit yield and quality of pineapple cultivated on tropical peat soil. Materials and methods. Six levels of K: 0, 266, 532, 798, 1064 and 1330 kg$\cdot$ha-1 K2O were applied at each of two pineapple plantations located at two different sites. The experiments were conducted with the Gandul cv. in a randomized complete block design with three replications. Results and discussion. The application of K had not any significant effect on plant height and leaf number of pineapple at both sites. Potassium significantly influenced the fruit diameter at site 1, and fruit length and fruit weight at site 2. The application of 266 kg$\cdot$ha-1 K2O resulted in the highest fruit weight and, at site 2, further increase of K declined it. Potassium had no significant effect on fruit sugar and acidity. However, at site 2, acid content tended to increase with increased K applications. Conclusion. Potassium applications at high rates tended to depress most of the growth and yield attributes of cv. Gandul pineapple cultivated on peat soil in Malaysia.

Introduction. Tendral type muskmelon is a winter melon fruit having a dark green skin slightly netted and crisp and a white sweet flesh with a long storage life. Materials and methods. The senescence of the mesocarp of the winter melon Cucumis melo L. (Inodorus Group) Tendral, stored at 12 °C and ca. 75% relative humidity, was investigated during 100 d after harvest. Results. During storage, starch and sucrose become increasingly hydrolysed while the levels of reducing sugars increased. In this period the firmness and titratable acidity decreased, but an increase was found for protein and lipoperoxide concentrations. The colour parameters L, a and b were also affected, b showing the largest increase after harvest. Ethylene concentration remained minimal but the production of carbon dioxide varied significantly. The activities of catalase and glutathione reductase increased whereas ascorbate peroxidase and superoxide dismutase were inhibited. Discussion. The senescence of winter melon Tendral is coupled to starch and sucrose consumption and to the synthesis of organic acids required for the respiratory metabolism. Hydrogen peroxide and superoxide also seem to accumulate, triggering the lipoperoxidation of cellular membranes at a low rate.