Contribution of corticular photosynthesis to bud development in African baobab (Adansonia digitata L.) and Castor bean (Ricinus communis L.) seedlings

The African baobab (Adansonia digitata L.) and castor bean (Ricinus communis L.) are drought resistant green-stemmed succulent plants which grow in the arid and semi-arid regions of Africa. Photosynthesis in the stems of green-stemmed plants is known to contribute to plant carbon gain especially during leafless periods. To study the contribution of stem photosynthesis in stem succulent plants, the height and stem diameter of baobab and castor bean plants grown in the greenhouse were measured. The plants were completely defoliated and subjected to different treatments: Watered with open stems (WO), watered and stems covered with aluminium foil (WC) to achieve 100% light exclusion, drought and open (DO) and drought and covered (DC). Stem coverage with aluminium foil resulted in a higher stem height and diameter during drought for baobab with similar trends seen in castor bean. Light exclusion resulted in a significantly lower bud DW production and enrichment in ¹³C in bud dry matter of castor bean and in stem dry matter of baobab. These show that corticular photosynthesis contributes in carbon gain in these species.     

Ethnic differences in use value and use patterns of baobab (Adansonia digitata L.) in northern Benin

The aim of this study was to combine qualitative and quantitative tools to evidence ethnic differences in use value and use patterns of baobab for the rural populations of northern Benin. The study was carried out in the municipalities of Boukoumbé and Karimama, focusing on Ottamari and Dendi ethnic groups, respectively, who have good knowledge on baobab uses. Ethnobotanical data were gathered through semi-structured individual interviews and processed by quantitative (multiple use curve, use value and fidelity level) and qualitative (flow chart) analytical and ethnobotanical methods. Leaves, fruit pulp and seeds of baobab were shown to be well-known for several food uses and were often the main ingredient in sauces, pastes, porridges and beverages. Medicinal uses were especially well-known for the bark, which was also used for making ropes. In both communities, a total of 38 different uses were mentioned for baobab products. There were significantly more uses known by the Ottamari than by the Dendi, with use values of 8 and 5, respectively. There were no differences detected in knowledge between sexes and age classes. As a result of its nutritional and high potential market value, preservation of ethnobotanical knowledge on baobab and exchange between communities is critical.     

Climate change and the African baobab (Adansonia digitata L.): the need for better conservation strategies

The baobab tree, with more than 300 uses and commercial value in EU and United States, has been identified as one of the most important trees to be conserved and domesticated in Africa. A decline in baobab populations because of changes in climate could have a negative effect on African livelihoods. Therefore, it is important to study the potential future distribution of this species and determine strategies for conservation. We used Maxent, 480 geo‐referenced records, present and future climatic and soil layers. Different general circulation models and scenarios were selected. Models were simulated for (i) All records, (ii) East Africa and (iii) West Africa species records. For each combination, the proportion of the present habitat that might remain suitable in the future was determined. These habitat proportions were compared with the Protected Areas in Africa. Although potential future distributions were different depending on model, scenario and records used, in all cases only a percentage of the present distribution was predicted to remain suitable in the future. Some countries were found to have no suitable habitat in the future. Recommendations for different conservation strategies include in situ conservation in Protected Areas; ex situ conservation in seed banks; and conservation through ‘sustainable utilization’.     

An optimized method for in vitro propagation of African baobab (Adansonia digitata L.) using two-node segments

Adansonia digitata L. (African baobab), is an important multi-purpose tree, whose distribution is at present limited to wild or semi-domesticated individuals widespread in Africa. Its distribution is threatened by seedling clearance for other land use and potentially by overharvesting induced by growing commercial use of baobab fruit. Recently, efforts have been made to establish baobab domestication and conservation strategies, with mixed results due to the low germinability of baobab seeds, a factor that hinders the possibility of developing commercial A. digitata plantations. Here, micropropagation was tested as a method for clonal propagation of explants from in vivo-grown seedlings. In vitro shoot multiplication was achieved by enhanced axillary bud proliferation of sterilized two-node segments. Bud break was dependent on cytokinin supply, but the combination of 1.0 or 10.0 μM zeatin riboside and 10.0 μM indole-3-butyric acid (IBA) increased the formation of microshoots after 8 weeks of culture. Regenerated microshoots rooted successfully in in vitro nutrient medium containing 10.0 μM IBA and normally grew in a greenhouse after acclimatization.     

Breeding for high production of leaves of baobab (Adansonia digitata L) in an irrigated hedge system

This study presents an evaluation of an irrigated “market garden” trial established with 3-month-old seedlings of baobab. The trial included offspring from 59 open-pollinated family lots from ten provenances and four bulked provenance sample lots. Leaf productivity and seedling growth were evaluated monthly from the third month after establishment. We found lowered leaf productivity during the dry season despite the plants being irrigated. We provide the first estimates of heritability for leaf production and growth of the species. We assumed that the families of seed from open-pollinated single trees consist of true half-sibs but also provided adjusted estimates assuming a high level of selfing. Differences among provenances and families within provenances were highly significant (p?<?0.01) with respect to leaf productivity. Heritability estimates (adjusted and non-adjusted) for leaf productivity were moderate to low, predicting moderate genetic gain from selection. Strong genetic and phenotypic correlations were estimated between diameter and leaf production, indicating that simple selection for diameter can efficiently increase leaf production. The dry weight/fresh weight ratio was not significantly different among provenances or families within provenances. Based on the findings, we discuss how breeding can increase the total leaf production and its seasonal distribution.     

Chloroplast DNA phylogeography suggests a West African centre of origin for the baobab, Adansonia digitata L. (Bombacoideae, Malvaceae)

The African baobab ( Adansonia digitata L.) is an emblematic, culturally important, and physically huge tropical tree species whose natural geographical distribution comprises most of tropical Africa, but also small patches of southern Arabia, and several Atlantic and Indian Ocean islands surrounding the African continent, notably including Madagascar. We analysed the polymerase chain reaction–restriction fragment length polymorphism of five chloroplast DNA fragments obtained from 344 individuals of A. digitata collected from 74 populations covering the entire extant distribution range of the species. Our goal was to reconstruct the phylogeographical history of the species and, if possible, to identify its centre of origin, which has been a subject of controversy for many decades. We identified five haplotypes whose distribution is clearly geographically structured. Using several species of Adansonia and of closely related genera as outgroups, the haplotypes showed a clear phylogeographical pattern of three groups. Two are phylogenetically related to the outgroup taxa, and are distributed in West Africa. The third group is substantially more differentiated genetically from outgroup species, and it corresponds to southern and eastern Africa, Arabia and the Indian Ocean islands, including Madagascar. According to our results, the tetraploid A. digitata , or its diploid progenitor, probably originated in West Africa and migrated subsequently throughout the tropical parts of that continent, and beyond, by natural and human-mediated terrestrial and overseas dispersal.     

A 1000-Year Carbon Isotope Rainfall Proxy Record from South African Baobab Trees (Adansonia digitata L.)

A proxy rainfall record for northeastern South Africa based on carbon isotope analysis of four baobab (Adansonia digitata L.) trees shows centennial and decadal scale variability over the last 1,000 years. The record is in good agreement with a 200-year tree ring record from Zimbabwe, and it indicates the existence of a rainfall dipole between the summer and winter rainfall areas of South Africa. The wettest period was c. AD 1075 in the Medieval Warm Period, and the driest periods were c. AD 1635, c. AD 1695 and c. AD1805 during the Little Ice Age. Decadal-scale variability suggests that the rainfall forcing mechanisms are a complex interaction between proximal and distal factors. Periods of higher rainfall are significantly associated with lower sea-surface temperatures in the Agulhas Current core region and a negative Dipole Moment Index in the Indian Ocean. The correlation between rainfall and the El Niño/Southern Oscillation Index is non-static. Wetter conditions are associated with predominantly El Niño conditions over most of the record, but since about AD 1970 this relationship inverted and wet conditions are currently associated with la Nina conditions. The effect of both proximal and distal oceanic influences are insufficient to explain the rainfall regime shift between the Medieval Warm Period and the Little Ice Age, and the evidence suggests that this was the result of a northward shift of the subtropical westerlies rather than a southward shift of the Intertropical Convergence Zone.     

Evaluation of oxidative stress tolerance in maize (Zea mays L.) seedlings in response to drought

Seedlings of selected six genotypes of maize (Zea mays L.) differing in their drought sensitivity (LM5 and Parkash drought-tolerant and PMH2, JH3459, Paras and LM14 as drought-sensitive) were exposed to 72 h drought stress at two leaf stage. Alterations in their antioxidant pools combined with activities of enzymes involved in defense against oxidative stress were investigated in leaves. Activities of some reactive oxygen species (ROS)-scavenging enzymes, catalase (CAT) and ascorbate peroxidase (APX) were enhanced in tolerant genotypes in response to drought stress. Superoxide dismutase (SOD) activity was significantly decreased in sensitive genotypes, but remained unchanged in tolerant genotypes under stress. Peroxidase (POX) activity was significantly induced in tolerant, as well as sensitive genotypes. Imposition of stress led to increase in H2O2 and malondialdehyde (MDA, a marker for lipid peroxidation) content in sensitive genotypes, while in tolerant genotypes no change was observed. Significant increase in glutathione content was observed in sensitive genotypes. Ascorbic acid pool was induced in both tolerant and sensitive genotypes, but induction was more pronounced in tolerant genotypes. Significant activation of antioxidative defence mechanisms correlated with drought-induced oxidative stress tolerance was the characteristic of the drought tolerant genotypes. These studies provide a mechanism for drought tolerance in maize seedlings.     

Pinpointing baobab (Adansonia digitata [Linn. 1759]) population hotspots in the semi-arid areas of Tanzania

The impact of unsustainable land-use conversions, changes in climate and anthropogenic activities on abundance and distribution of baobab populations was assessed in semi-arid regions of Tanzania. Baobabs were sampled in plots of 1 km long and a 50 m wide, which were carried out in 337 grids located in different land-use types. Transects for each land-use type were located using a stratified random sampling technique to compare baobab population variations and occurrences in semi-arid areas of Tanzania. Baobab density was found to be highest in strictly protected areas and the lowest density in unprotected areas, suggesting that anthropogenic activities coupled with local management practices within land-uses may be influencing its viability in semi-arid areas. In species like this, with less and slow recruitment rate, it takes a long time to bring the population to recovery when substantial disturbance and overutilisation have reduced the populations to certain levels. Thus, increased human and climate change pressures on land are likely to drive the species to extinction in these fragmented populations.     

The Use of Baobab Leaves (Adansonia digitata L.) for Food in Africa: A Review

Economic Botany - The Use of Baobab Leaves (Adansonia digitata) for Food in Africa: A Review. The massive long-lived African baobab (Adansonia digitata L.) is a celebrated member of a small...     

The response of carrot (Daucus carota L.) and onion (Allium cepa L.) seedlings to mechanical impedance and water stress at sub-optimal temperatures

The response of pre-emergent shoots of carrot and onion to mechanical impedance, water stress and suboptimal temperature was studied. We used model laboratory systems in which mechanical impedance and water stress could be varied independently of each other and independently of other complicating factors (e.g. aeration and hydraulic conductivity). Our results showed that mechanical impedance reduced the rate and extent of shoot development in both carrot and onion. Roots of both carrot and onion were less sensitive to mechanical impedance than shoots. The recovery of shoot length following the removal of impedance was studied. The data were used to develop a new model of shoot elongation as a function of mechanical stress, water stress, temperature, shoot length and time. Our results also provide a new insight into the physiology of shoot development in strong soils. We contrast the effect of mechanical impedance on pre-emergent seedling development in carrot and onion.     

Patterns of genetic and morphometric diversity in baobab (Adansonia digitata) populations across different climatic zones of Benin (West Africa)

BACKGROUND AND AIMS: Baobab (Adansonia digitata) is a multi-purpose tree used daily by rural African communities. The present study aimed at investigating the level of morphometric and genetic variation and spatial genetic structure within and between threatened baobab populations from the three climatic zones of Benin. METHODS: A total of 137 individuals from six populations were analysed using morphometric data as well as molecular marker data generated using the AFLP technique. KEY RESULTS: Five primer pairs resulted in a total of 217 scored bands with 78.34 % of them being polymorphic. A two-level AMOVA of 137 individuals from six baobab populations revealed 82.37 % of the total variation within populations and 17.63 % among populations (P < 0.001). Analysis of population structure with allele-frequency based F-statistics revealed a global F(ST) of 0.127 +/- 0.072 (P < 0.001). The mean gene diversity within populations (H(S)) and the average gene diversity between populations (D(ST)) were estimated at 0.309 +/- 0.000 and 0.045 +/- 0.072, respectively. Baobabs in the Sudanian and Sudan-Guinean zones of Benin were short and produced the highest yields of pulp, seeds and kernels, in contrast to the ones in the Guinean zone, which were tall and produced only a small number of fruits with a low pulp, seed and kernel productivity. A statistically significant correlation with the observed patterns of genetic diversity was observed for three morphological characteristics: height of the trees, number of branches and thickness of the capsules. CONCLUSIONS: The results indicate some degree of physical isolation of the populations collected in the different climatic zones and suggest a substantial amount of genetic structuring between the analysed populations of baobab. Sampling options of the natural populations are suggested for in or ex situ conservation.     

Spatial genetic structuring of baobab (Adansonia digitata, Malvaceae) in the traditional agroforestry systems of West Africa

This study evaluates the spatial genetic structure of baobab (Adansonia digitata) populations from West African agroforestry systems at different geographical scales using AFLP fingerprints. Eleven populations from four countries (Benin, Ghana, Burkina Faso, and Senegal) had comparable levels of genetic diversity, although the two populations in the extreme west (Senegal) had less diversity. Pairwise F(ST) ranged from 0.02 to 0.28 and increased with geographic distance, even at a regional scale. Gene pools detected by Bayesian clustering seem to be a byproduct of the isolation-by-distance pattern rather than representing actual discrete entities. The organization of genetic diversity appears to result essentially from spatially restricted gene flow, with some influences of human seed exchange. Despite the potential for relatively long-distance pollen and seed dispersal by bats within populations, statistically significant spatial genetic structuring within populations (SGS) was detected and gave a mean indirect estimate of neighborhood size of ca. 45. This study demonstrated that relatively high levels of genetic structuring are present in baobab at both large and within-population level, which was unexpected in regard to its dispersal by bats and the influence of human exchange of seeds. Implications of these results for the conservation of baobab populations are discussed.     

Assessment of grain yield indices in response to drought stress in wheat (Triticum aestivum L.)

Drought stress constricts crop production in the world. Increasing human population and predicted temperature increase owing to global warming will lead ruthless problems for agricultural production in near future. Hence, use of high yielding genotypes having drought tolerance and scrutinize of drought sensitive local cultivars for making them tolerant may be the proficient approaches to cope its detrimental outcomes. The current study was executed during 20015–2016 and 2016–2017 in field using randomized complete block design under factorial arrangements on 50 wheat genotypes for exploring their sensitivity and tolerance against drought. Some of the attributes of grain yield and drought tolerance indices were recorded. Grain yield showed negative correlations with tolerance index (TOL), drought index (DI) and stress susceptibility index (SSI) while positive correlation with mean productivity (MP) and geometric mean productivity (GMP) under drought condition. These findings depicted that tolerant genotypes could be chosen by high MP and GMP values and low SSI and TOL values. Based on the results, genotypes GA-02, Faisalabad-83, 9444, Sehar-06, Pirsabak-04 and Kohistan-97 were more tolerant and recognized as suitable for both normal and drought conditions. Genotypes of Chenab-00, Kohsar-95, Parwaz-94 and Kohenoor-83 confirmed more sensitive due to high grain yield loss under drought stress.     

The response of European beech (Fagus sylvatica L.) seedlings from two Italian populations to drought and recovery

The response of gas exchange, leaf chlorophyll content, relative fluorescence to decreasing water potential and recovery was followed in European beech seedlings from two Italian populations, differing in their native precipitation amounts. A population from Sicily (southern Italy) was selected as representative of a xeric population while a population from central Italy, Abetone, represented a mesic one. Dry-matter partitioning, leaf area, hydraulic sufficiency and xylem embolism were evaluated in both well-watered control plants as well as in plants subjected to drought. With the onset of water stress, values of water potential, leaf relative water content, net photosynthesis, leaf conductance and leaf chlorophyll concentration decreased concurrently while relative fluorescence remained unchanged. The population from Sicily showed a delay in effects of the imposed drought. Within 5 days of rewatering, leaf conductance was not fully recovered while all of the other parameters recovered to control levels, in both populations. Total, shoot, stem and root dry weight tended to be higher in seedlings from Abetone, even though both populations had similar photosynthetic rates. The population from Sicily exhibited about 3% greater (even if not significant) allocation to roots than the population from Abetone. Seedlings from Abetone had higher, but not significant, leaf specific conductivity and per cent loss in hydraulic conductivity than seedlings from Sicily. Drought resulted in a reduction of hydraulic conductivity and hydraulic sufficiency in seedlings from both populations. Photosynthesis of water stressed plants from both populations appeared to be reduced primarily by carbon dioxide diffusion through stomata and perhaps secondarily by changes in chlorophyll concentration rather than by efficiency of photosystem II. The effect of hydraulic factors on gas exchange during drought and recovery was not clearly evident.     

Ammonium nutrition increases water absorption in rice seedlings (Oryza sativa L.) under water stress

Water stress is a primary limitation on plant growth. In previous studies, it has been found that ammonium enhances the tolerance of rice plants to water stress, but how water is related to nitrogen form and water stress remains unknown. To study the effects of nitrogen form (NH ₄ ⁺ , NO ₃ ^? , and a mixture of NH ₄ ⁺ and NO ₃ ^? ) on the growth and water absorption of rice (Oryza sativa L.) seedlings, a hydroponic experiment with water stress, simulated by the addition of polyethylene glycol (PEG, 10% w/v, MW 6000), was conducted in a greenhouse. The results showed that, compared with non-water stress, under water stress, the fresh weight of rice seedlings increased by 14% with NH ₄ ⁺ nutrition, whereas it had decreased by about 20% with either NO ₃ ^? or mixed nitrogen nutrition. No significant difference was found in the transpiration rate of excised shoots or in xylem exudation of excised roots in NH ₄ ⁺ supply between the two water situations, whereas xylem flow decreased by 57% and 24% under water stress in NO ₃ ^? and mixed nutrition, and root hydraulic conductivity decreased by 29% and 54% in plants in NH ₄ ⁺ and NO ₃ ^? nutrition conditions, respectively. Although water absorption ability decreased in both NH ₄ ⁺ and NO ₃ ^? nutrition, aquaporin activity was higher in NH ₄ ⁺ than in NO ₃ ^? nutrition, regardless of water stress. We conclude that NH ₄ ⁺ nutrition can improve water handling in rice seedlings and subsequently enhance their resistance to drought.     

Epigenetic responses to drought stress in rice (Oryza sativa L.)

Cytosine methylation polymorphism plays a key role in gene regulation, mainly in expression of genes in crop plants. The differential expression of cytosine methylation over drought stress response was analyzed in rice using drought susceptible but agronomically superior lines IR 20 and CO 43, and drought tolerant genotypes PL and PMK 3 and their F₁ hybrids. The parents and hybrids were subjected to two moisture regimes viz., one under drought condition and another under control condition. The cytosine methylation polymorphism in genomic DNA was quantified under both the conditions at the reproductive stage of the plant using the Methylation Sensitive Amplified Polymorphism (MSAP) technique devised by Xiong et al. (261:439–446, 1999). The results depicted that under drought condition, hyper-methylation was predominant in the drought susceptible genotypes while drought tolerant genotypes presented hypo-methylation behavior. While imposing drought, spikelet sterility per cent was positively correlated to percentage of methylation whereas, panicle length, number of seed per panicle, panicle weight, 100 seed weight, and yield/plant were negatively correlated indicating the role of epigenetic regulation in yield attributing traits in response to drought. Thus, methylation can be considered as an important epigenetic regulatory mechanism in rice plants to adapt drought situation. From this study, we speculate that the hyper- methylation may be an indicator of drought susceptibility and the hypo-methylation for drought tolerance and this methylation polymorphism can be effectively used in drought screening program.     

Genotypic variation between maize (Zea mays L.) single cross hybrids in response to drought stress

Effects of soil drought on growth and productivity of 16 single cross maize hybrids were investigated under field and greenhouse experiments. The Drought Susceptibility Index (DSI) was evaluated in a three year field experiment by the determination of grain loss in conditions of two soil moisture levels (drought and irrigated) and in a pot experiment by the effects of periodical soil drought on seedling dry matter. In the greenhouse experiment response to drought in maize genotypes was also evaluated by root to shoot dry mater ratio, transpiration productivity index, indexes of kernel germination and index of leaf injury by drought and heat temperature. The obtained values of DSI enabled the ranking of the tested genotypes with respect to their drought tolerance. The values of DSI obtained in the field experiment allow to divide the examined genotypes into three, and in the greenhouse experiment into two groups of drought susceptibility. The correlation coefficients between the DSI of maize hybrids in the field and the greenhouse experiments was high and statistically significant, being equal to 0.876. The ranking of hybrids drought tolerance, identified on the basis of field experiments was generally in agreement with the ranking established on the basis of the greenhouse experiment. In the greenhouse experiment statistically significant coefficients of correlation with DSI values in hybrids were obtained for the ratio of dry matter of overground parts to dry matter of roots, both for control and drought treatments, whereas in the estimation of the transpiration productivity coefficient and total dry matter the correlation coefficients were not statistically significant. In this study several laboratory tests were carried out for the drought tolerance of plants (kernel germination, leaf injury) on 4 drought resistant and 4 drought sensitive maize hybrids. Statistically significant correlation coefficients between DSI and the examined parameter of grain germination and leaf injury were obtained for the determination of promptness index (PI), seedling survival index (SS) and leaf injuries indexes (IDS, ITS) as a result of exposure to 14 days of soil drought, osmotic drought −0.9 MPa and exposure to high temperature 45 ° or 50 °C. The results of laboratory tests show that in maize the genetic variation in the degree of drought tolerance is better manifested under severe conditions of water deficit in the soil.