Germination responses of Cola acuminata (Pal. De Beauv.) seeds to different substrates, photoperiods and dehydration

Cola acuminata (Pal. De Beauv.), one of the many forest tree species which are of socio-economic importance in Western and Central Africa, is still exploited in the wild by subsistence farmers because it has not been domesticated yet. As a contribution to its domestication, the present study aimed at determining germination requirements and desiccation tolerance of seeds. Three substrates (forest topsoil, river sand and mixture of forest top soil and river sand), two photoperiods (12 hours/day and continuous darkness) and dehydration were investigated for their effects on seeds germination percentage. To evaluate the seeds’ tolerance to desiccation, fresh seeds were dried at laboratory temperature for 16 days during which seeds moisture content, seeds germination percentage and electrical conductivity of seeds leachate were monitored at two-day intervals. Results showed that the mean germination percentage recorded on the mixture of forest top soil and river sand (97.2 ± 1.0%) was significantly higher than that recorded on forest topsoil (85.5 ± 4.0%), which was in turn higher than that obtained on river sand (70 ± 1.5%). The effect of photoperiod on germination percentage was not significant (p = 0.112). As response to seeds drying, the mean germination percentage slightly decreased as moisture got lost, then drastically dropped when moisture content was below 45.95 ± 4.2%. Seeds failed to germinate when their moisture content fell below 27.1 ± 2.1%. Electrical conductivity of seed leachate exhibited a highly significant negative correlation with both germination percentage (p ˂ 0.01, r = -0.926) and moisture content (p ˂ 0.01, r = -0.931). It is concluded that the best substrate for C. acuminata seeds’ germination is the mixture of forest top soil and river sand in a 1/1 (v/v) ratio. Cola acuminata seeds are desiccation-sensitive and their storage behavior is recalcitrant. This is a significant constraint for conservation that should be addressed in further researches.Keywords: Cola acuminate, seed germination, photoperiod, desiccation tolerance, moisture content, storage behavior

Germination of Cola anomala (K. Shum.) Shott and Endl seeds: effects of provenance, substrate and dehydration

As a step in the process of Cola anomala domestication, investigations were undertaken on germination requirements and desiccation tolerance of its seeds. Three seed provenances (Bamenda, Bayangam and Dschang), three substrates (forest top soil, river sand and a mixture of forest top soil and river sand) and two photoperiods (12 hours/day and, continuous darkness) were investigated for their effects on seed germination. To evaluate their desiccation tolerance, fresh seeds were dried at room temperature for 16 days during which seed moisture content, seed germination percentage and electrical conductivity of seed leachate were monitored at two-day intervals. Results showed that germination percentages were significantly (P < 0.05) higher both on forest top soil alone (86.04 ± 4.8%), and on a mixture of forest top soil and river sand (83.56 ± 4.5%), than on river sand alone (69.96 ± 4.7%). Seeds from Bamenda showed a higher germination percentage (91.4 ± 4.7%) than those from either Bayangam (77.36 ± 4.7%) or Dschang (70.8 ± 4.8%). The desiccation tolerance test revealed that as response to drying, the mean germination percentage was first slightly reduced as moisture was lost, then declined considerably at moisture content below 50.28%. Total germination failure was observed when seed moisture reached 32.24%. Electrical conductivity of seed leachate exhibited a strong correlation with loss of viability as well as with desiccation. It is concluded that there is a provenance-related variation in C. anomala seed germination. The best substrate for germination is forest top soil supplemented or not with river sand in a 1/1 (v/v) ratio. C. anomala seeds are desiccation-sensitive and their storage behaviour is recalcitrant.Keywords: Desiccation tolerance, critical moisture, lethal moisture, electrical conductivity, electrolyte leakage, storage behaviour

Nutrient flows in smallholder production systems in the humid forest zone of southern Cameroon

The flows and balances of N, P and K were studied in 20 farms in the Campo Ma'an area in Cameroon between March and August 2002 to assess the nutrient dynamics in smallholder farms. Data were collected through farmer interviews, field measurements and estimates from transfer functions. Nutrient input from mineral (IN1), animal feed (IN2a) and inorganic amendments (IN2b) was absent. Major outputs were through crop (OUT1a) and animal (OUT1b) products sold. Partial budgets for farmer managed flows were negative: -65 kg N, -5.5 kg P and -30.8 kg K ha-1 year-1. For inflows not managed by farmers, deep capture (IN6) was the major source: 16.6, 1.4 and 6.6 kg ha -1 year-1 of N, P and K, respectively. Atmospheric deposition (IN3) was estimated at 4.3 kg N, 1.0 kg P and 3.9 kg K ha -1 year-1, and biological nitrogen fixation (IN4) at 6.9 kg N ha-1 year-1. Major losses were leaching (OUT 3a): 26.4 kg N, and 0.88 kg K ha-1 year-1. Gaseous losses from the soil (OUT 4a) were estimated at 6.34 kg N, and human faeces (OUT 6) were estimated at 4 kg N, 0.64 kg P and 4.8 kg K ha-1 year-1. The highest losses were from burning (OUT 4c), i.e. 47.8 kg N, 1.8 kg P and 14.3 kg K ha-1 year-1. Partial budgets of environmentally controlled flows were negative only for N -4.8 kg N, +2.4 kg P and +9.6 kg K ha-1 year-1. The overall farm budgets were negative, with annual losses of 69 kg N, 3 kg P and 21 kg K ha-1. Only cocoa had a positive nutrient balance: +9.3 kg N, +1.4 kg P and +7.6 kg K ha-1 year-1. Nutrients reaching the household waste (1.9 kg N, 2.8 kg P and 18.8 kg K ha-1 year-1), animal manure (4.9 kg N, 0.4 kg P and 1.6 kg K), and human faeces (4 kg N, 0.64 kg P and 4.8 kg K ha -1 year-1) were not recycled. Five alternative management scenarios were envisaged to improve the nutrient balances. Recycling animal manure, household waste and human faeces will bring the balance at -62.6 kg N, 0 kg P and +1 kg K ha-1 year-1. If, additionally, burning could be avoided, positive nutrient balances could be expecte

Établissement de typologies de retenues par traitement de séries temporelles d’images Sentinel

Les retenues d’eau peuvent jouer plusieurs rôles et peuvent être de plusieurs utilités en fonction des besoins. Elles existent depuis plusieurs siècles et ont servi pour le stockage de l’eau dans le but d’alimenter des moulins à eau, pour la production électrique, l’irrigation des cultures, etc. Au fil du temps, ces dernières n’ont pas vraiment eu des rôles différents et leur principal usage reste l’irrigation. Ces dernières années dans le monde et plus précisément dans les pays chauds comme la Tunisie et dans les zones où il fait chaud à certains moments de l’année (Sud de la France par exemple), on fait face à un phénomène climatique (aridification) qui met en péril plusieurs secteurs notamment l’agriculture. Pour adapter leurs pratiques agricoles, les agriculteurs ont opté pour la construction des réservoirs d’eau communément appelés « retenues d’eau ». Pour soutenir les différents acteurs face à ces changements climatiques, le gouvernement français a également décidé de mettre sur pied des projets de territoire pour la gestion de l’eau (PTGE) afin de mieux partager les ressources en eau entre les différents acteurs. .../..

Germination of

 Introduction. Despite its socio-economic importance, cultivation of Garcinia kola Heckel is very limited due to poor seed germination. The literature gives contradictory information concerning this fact. Our study therefore aimed at (1) evaluating the variability in germination traits among seeds collected from different areas of Cameroon; and (2) testing the efficiency of some hormone treatments in improving the seed germination rate, which would promote cultivation of G. kola by rural farmers. Materials and methods. Six collections of seeds originating from six locations in Cameroon were subjected to pre-sowing treatments; soaking for 3 days at room temperature in cool distilled water (control), or in cool distilled water supplemented with either 10-4 M gibberellic acid (GA3), 10-4 M naphthalene acetic acid (NAA), 10-4 M 2,4-dichlorophenoxyacetic acid (2,4-D), 10-4 M benzylaminopurine (BAP) or 10-4 M kinetin; they were then placed to germinate in laboratory conditions. Cumulative seed germination data were recorded for 30 weeks. Results. The pre-germination treatments had profound effects on the phenology of G. kola seed germination. Multiple shoots, multiple roots and callus formation were induced from seeds soaked in BAP, NAA and 2,4-D solutions, respectively. Analysis of variance showed a significant effect (p < 0.01) of seed collection on the germination velocity. Although the rate of germination was higher and the complete dormancy period lower in seeds treated with NAA than in seeds with other treatments, none of these seed treatments significantly enhanced germination. Conclusion. Variations in phenology responses of G. kola seeds to hormone treatments indicate that the tissues of this plant may be responsive in in vitro culture. Variations in seed germination velocity among collections may explain the current controversy over G. kola seed germination, and could help in further selection and domestication processes of this species