Alien chromosome transmission and somatic elimination in monosomic addition lines of Gossypium australe F. Muell in G. hirsutum L.

The efficiency of using monosomic alien addition lines (MAALs) to introgress agronomical traits of interest carried by wild diploid Gossypium species into the main cultivated cotton species G. hirsutum depends on the opportunities of confronting the alien chromosome with the recipient background genome at each generation and on the occurrence of translocations and homoeologous recombinations. The selfed-progeny of five MAALs of G. australe in G. hirsutum was screened with SSR markers to determine the transmission frequency of the alien chromosome and monitor its integrity. Three MAALs revealed a transmission frequency significantly lower than the expected ratio and one MAAL presented an exclusive transmission of the additional chromosome. In these four MAAL the alien chromosome was transmitted almost unaltered. With the fifth MAAL the alien chromosome was normally transmitted but was altered in half of the plants carrying it. In one MAAL, normally carrying brown fiber, the emergence of some plants carrying white and brown fiber revealed the somatic elimination of the additional chromosome. The loss of this chromosome seems to be triggered by its deletion.     

西非Sudanian热带林地11个树种地上生物量异速生长预测

Allometric models are necessary for estimating biomass in terrestrial ecosystems. Generalized allometric relationship exists for many tropical trees, but species- and region-specific models are often lacking. We developed species-specific allometric models to predict aboveground biomass for 11 native tree species of the Sudanian savanna-woodlands. Diameters at the base and at breast height, with species means ranging respectively from 11 to 28 cm and 9 to 19 cm, and the height of the trees were used as predictor variables. Sampled trees spanned a wide range of sizes including the largest sizes these species can reach. As a response variable, the biomass of the trees was obtained through destructive sampling of 4 754 trees during wood harvesting. We used a stepwise multiple regression analysis with backward elimination procedure to develop models separately predicting, total biomass of the trees, stem biomass, and biomass of branches and twigs. All species-specific regression models relating biomass with measured tree dimensions were highly significant (p < 0.001). The biomass of branches and twigs was less predictable compared to stem biomass and total biomass, although their models required fewer predictors and predictor interactions. The best-fit equations for total above-ground biomass and stem biomass had R ² > 0.70, except for the Acacia species; for branches including twig biomass, R²-values varied from 0.749 for Anogeissus leiocarpa to 0.183 for Acacia macrostachya. The use of these equations in estimating available biomass will avoid destructive sampling, and aid in planning for sustainable use of these species.     

西非Sudanian稀树草原森林在旱季火烧温度、持续时间及对种子萌发的影响

Prescribed fire is used in the Sudanian savanna-woodland of West Africa as a forest management tool. An experiment was carried out to assess the effects of season of burning, and different vertical probe positions on maximum fire temperature and temperature residence time above 60°C which is considered lethal for plant tissues. Seasons of burning considered were: an early season fire set at the beginning of the dry season (beginning of December), mid-season fire set at the peak of the dry season (mid-January), and a late season fire at the end of the dry season (end of March). The effects of these fires on the germination of buried seeds of three socio-economically valuable tree species were also examined. Results indicated significant differences in maximum fire temperature and residence time with respect to season of burning and vertical probe position (p < 0.001). The highest and longest lasting temperatures were observed at 20 cm above ground during early fire and at the soil surface during mid-season and late fires. This, in turn, affected germination responses of seeds buried at different soil depths. Implications of these findings in the current management practices are discussed.     

Dominant species’ resprout biomass dynamics after cutting in the Sudanian savanna-woodlands of West Africa: long term effects of annual early fire and grazing

Background   

The potential of forest to regenerate after harvesting is a key element for sustainability of the ecosystem. For semi-arid tropical savanna environments, managing resprouts after tree cutting is ideally suited because of the natural ability of many indigenous species to regenerate vegetatively. Regeneration in this ecosystem is, however, prone to many disturbance factors such as fire and grazing by livestock.     

Seed germination of herbaceous and woody species of the Sudanian savanna-woodland in response to heat shock and smoke

Fire-related cues (smoke and heat) contribute largely to changes in vegetation communities in fire prone habitats. The germination responses of seeds of species from Combretaceae, Leguminosae and Poaceae to smoke, heat or their interaction were examined. Half of the seed batch was first exposed to cold aerosol smoke for 60 min. Untreated and smoked seed batches were then subjected to heat treatment by incubating them at 40 °C, 80 °C or 120 °C for 2.5 min. The results showed that the seed germination of fire-adapted species, Terminalia avicennioides (p < 0.01) and Pteleopsis suberosa (p < 0.05), was stimulated by smoke, while the germination of fire-sensitive species, Anogeissus leiocarpus (p < 0.001) and Andropogon gayanus (p < 0.05) was inhibited by heat and smoke, respectively. Seeds of fire-tolerant species (Combretum glutinosum and Combretum nigricans) germinated favorably in response to heat and smoke treatments. The germination response of leguminous species was not significant with respect to the smoke and heat levels applied. In conclusion, there was no persistent pattern across all species that can easily explain their responses to fire-related cues, which can be related to species-specific requirements for a given dosage–response level, which in turn is attributed to the levels of heat shock and smoke treatments adopted in the present study. Testing different exposure times to heat shock and varying doses of smoke on large number of species is needed before generalization about community level response to fire could be drawn.     

Influence of long-term organic and mineral fertilization on soil nematofauna when growing Sorghum bicolor in Burkina Faso

Soil degradation has led crop yield to decline in many Sahelian countries and is a fundamental agricultural and economical threat for local populations. In Saria, Burkina Faso, long-term experiments are being performed to find efficient soil management practices that could improve soil fertility. A randomized block experiment comprising organic amendment (unamended control, straw at 8.3 t ha⁻¹, manure at 10 t ha⁻¹) coupled with mineral fertilization (no urea, urea at 60 kg ha⁻¹) was started in 1980 with a continuous sorghum (Sorghum bicolor) cropping system. Twenty-six years after the settlement of the treatments, we compared their effects on nematode populations, community structure, and ecological indices, as well as soil physical and chemical properties at three stages of sorghum’s cropping cycle.     

Soil carbon and nitrogen dynamics linked to Piliostigma species in ferugino-tropical soils in the Sudano-Sahelian zone of Burkina Faso, West Africa

In the Sudano-Sahelian zone of Burkina Faso, Piliostigma reticulatum (DC) Hochst and Piliostigma thonningii (Schumach) are precursor species of fallow land colonization and they are used by rural villagers. The present study aimed to assess the contribution of Piliostigma species to soil quality improvement. We quantified organic carbon, total nitrogen, soil microbial biomass, soil basal respiration and metabolic quotient from soil samples taken under and outside Piliostigma canopies. We used one-way ANOVA to test for differences in the above parameters between locations (beneath and outside Piliostigma canopies). We recorded increased total organic carbon under Piliostigma from 31%-105% and in total nitrogen from 23%-66%. Microbial biomass was13%-266% higher beneath canopies as compared to outside canopies. Basal respiration was also higher beneath canopies. The chemical elements varied by class of soil texture. Metabolic quotient (qCO2 ) was significantly correlated to clay (r=0.80) and silt (r=0.79) content. Piliostigma stands produced abundant litter due to their leaf biomass. Thus, they contribute to improved total organic carbon and total nitrogen content in the different phytogeographic zones and improve soil fertility