Cowpea seed quality in response to production site and water stress.

Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.Cowpea (Vigna unguiculata. L) is an important African crop. However, it is also an underutilized grain legume. Consequently, there is not enough research data on cowpea seed physiology. Whereas there is evidence of cowpea being a drought tolerant crop, there is no evidence to associate plant drought tolerance with seed quality in response to water stress. This study sought to understand the effect of production site and water stress on cowpea seed quality development with respect to germination capacity and vigour. Patterns of raffinose family of oligosaccharides (RFO) during seed development to mature dry stage were used to physiologically relate seed performance to water stress. The effect of water stress and exogenous ABA on the accumulation of stress LEA proteins (dehydrins) in relation to seed quality development and germination was investigated. RFOs are known for their roles in desiccation sensitivity but no studies have shown their significance in cowpeas. Seeds of six cowpea cultivars were produced at two distinct growth sites characterised by irrigated and dry land conditions. The seeds were assessed during six developmental stages, for water content, dry matter accumulation, and performance. Harvested seeds were then planted in a pot experiment under controlled conditions to examine the effect of water stress on seed quality development and data collected during three developmental stages. Harvested seeds from the pot experiment were subsequently analyzed for changes in RFO accumulation during development using gas chromatography. The seeds were also used to investigate the effect of water stress and ABA on the accumulation of stress LEA proteins (dehydrins) in relation to seed quality development in cowpea. In addition, this study evaluated the use of image analysis as a method that can be used to objectively determine seed coat colour variation in cowpea. Statistical variation in individual seed’s solute leakage for cowpea cultivars differing in seed coat colour and produced under different environmental conditions was explored and correlations were done between seed conductivity test with other aspects of seed performance during germination. Furthermore the results of the conductivity test were compared with accelerated aging test, in relation to seed performance. The study provided evidence that cowpea seed lots produced under different environmental, and possibly management conditions may not differ with respect to seed quality as determined by germination capacity and vigour. However, significant differences between sites with respect to seed maturation patterns determined by water content and dry matter accumulation were observed. Adverse maternal environmental effects on the subsequent performance of seeds in a drought tolerant crop may not necessarily lead to poor performance. Cultivar differences in response to simulated drought conditions at the whole plant and tissue level can be considerable and highly variable; however, these differences may not have adverse effects on the germination and vigour of the seeds. Drought avoidance mechanisms at the whole plant level in cowpea are quite efficient in allowing the species to adapt to simulated drought conditions. These mechanisms may allow the cowpea cultivars to maintain metabolism and restore conditions for their continued growth under water stress; and produce few seeds of high germination capacity and vigour. Stachyose was found to be the predominant member of the raffinose family of oligosaccharides in cowpea. It is suggested that stachyose accumulation could be used as an indicator of stress tolerance in cowpea. However, the relationship between RFO concentration and the acquisition of desiccation remained as a matter of speculation in the present study and is still generally inconclusive. There was no evidence to suggest the acquisition of maximum desiccation tolerance is associated with maximum seed vigour. It is suggested in cowpea, which is drought tolerant, that maximum vigour does not necessarily imply the acquisition of maximum desiccation tolerance; rather there is a minimum level of desiccation tolerance that is required for the development of optimal seed vigour. The use of an in vivo approach in the study of LEA function in cowpea enabled the accurate comparison of two different groups of LEA proteins in developing cowpea seeds under conditions of water stress and in relation to germination and vigour. Both group 1 LEA and group 2 LEA (dehydrin) were shown to increase in concentration in response to water stress. In addition group 1 LEA protein was observed to be relatively abundant in cowpea seeds. A maternal influence on LEA protein gene expression under conditions of water stress, which may induce dehydrin accumulation vii during the earlier stages of seed development, was implied by the observation that dehydrin-like proteins were induced after two weeks of development in cowpea plants subjected to stress during the vegetative phase. In addition, the exogenous application of ABA delayed radicle protrusion; this was associated with a delay in the disappearance of LEA proteins and is suggestive of a relationship between LEA protein accumulation and the acquisition of desiccation tolerance. The study has demonstrated that image analysis can objectively discriminate seed coat colour variation in cowpea. Dark coloured seeds in general performed better than light coloured seeds; however seed coat colour was not always associated with better performance. A newly developed Aging Stress Differential Index (ASDI) has been used in this study to demonstrate a link between seed coat colour and sensitivity to water stress. The ASDI correlated well with the observations relating stress tolerance to stachyose accumulation. The skewed distribution patterns in individual electrical conductivity and the presence of extreme values may have implications with respect to the suitability of using standard statistical analyses which compare mean values to evaluate such data. In addition variation in individual electrical conductivity may also be influenced by cultivar differences and the chemical composition of the seed coat. Therefore associations between seed coat colour and electrical conductivity as a measure of performance should be treated with caution. The AA test does reflect changes in seed vigour, however ranked electrical conductivity values after AA did not consistently reflect differences in seed performance between cultivars and sites, and they did not correlate well with other aspects of performance

Citron Watermelon Potential to Improve Crop Diversification and Reduce Negative Impacts of Climate Change

Citron watermelon (Citrullus lanatus var. citroides (L.H. Bailey) Mansf. ex Greb.) is an underexploited and under-researched crop species with the potential to contribute to crop diversification in Sub-Saharan Africa. The species is cultivated in the drier parts of Southern Africa, mainly by smallholder farmers who maintain a wide range of landrace varieties. Understanding the molecular and morpho-physiological basis for drought adaptation in citron watermelon under these dry environments can aid in the identification of suitable traits for drought-tolerance breeding and improve food system resilience among smallholder farmers, thus adding to crop diversification. This paper reviews the literature on drought adaptation of Citrullus lanatus spp. (C3 xerophytes), using the systematic review approach. The review discusses the potential role of citron watermelon in adding to crop diversification, alternative food uses, and potential by-products that can be processed from the crop, and it analyzes the role of Sub-Saharan African farmers play as key actors in conserving citron watermelon germplasm and biodiversity. Finally, the review provides a summary of significant findings and identifies critical knowledge gaps for further research

Integrated soil fertility management practices for improved crop production in smallholder farming systems of semi-arid areas: A synthetic review

AbstractSoil fertility degradation is one of the major constraints in smallholder farming environments especially in the semi-arid region of Sub-Saharan Africa. This has been worsened by poor farming methods, lack of technical knowledge and inadequate application of nutrient sources by farmers. The use of mineral fertiliser alone has been cost ineffective and causes land degradation. Although several soil fertility management (SFM) practices have been put forward, knowledge about their benefits, access and adoption by smallholder farmers is still limited. Synthetic review of published articles obtained from Web of Science, Google Scholar and Scopus which cover semi-arid regions across Africa were retrieved and synthesied. Farmers have been applying low organic manure (<5 t ha−1) against the recommended rate of 20–40 t ha−1 depending on soil texture and this caused low crop yields. This call for farmers to adopt integrated soil fertility management (ISFM) practices to improve nutrient availability and crop yields. The use of ISFM has been reported to increase maize yields by 15–145% in semi-arid areas. Maize yields varies from 4200 to 5500 kg ha−1 and sorghum from 690 to 3500 kg ha−1 under ISFM. Yield increment for various crops with the use of cattle manure integrated with other nutrient sources was reported but there are still few studies where effects compost, farmyard manure and poultry manure were combined with inorganic fertiliser were evaluated. Therefore, this review paper seeks to synthesise the effects of ISFM practices available for smallholder farming systems in semi-arid areas of sub-Saharan Africa to improve crop production

Selected micronutrients effect on growth, development, and yield of black nightshade (Solanum nigrum)

Abstract Black nightshade (Solanum nigrum) is an important indigenous leafy vegetable consumed in sub‐Saharan Africa. The species is an important source of micronutrients for medicinal purposes. A controlled experiment was conducted at the University of KwaZulu‐Natal, Pietermaritzburg, South Africa, to investigate the effect of zinc and boron applications on the growth, development, and yield of black nightshade. Each micronutrient (zinc and boron) was applied at five different concentrations, namely, 100 (T1), 200 (T2), 300 (T3), 400 (T4), and 500 (T5) ppm, including a control (T0) (distilled/high pressure liquid chromatography water spray), giving a total of six treatments. Treatments were arranged in a complete randomized design (CRD) with three replications, giving a total of 18 experimental units (pots). After 14 days of transplanting, the treatments were applied through foliar spraying three times over 24 h with an 8‐h interval between each spraying event. Data collection started 14 days after transplanting, and thereafter, measurements were taken fortnightly. At harvest (70 days after transplanting), fruit number, fresh shoot weight, dry shoot weight, root fresh mass, and root dry mass were determined. The results showed significant growth and yield differences with respect to the different concentrations of zinc and boron (p < 0.05). The application of 500 ppm of boron performed significantly better than all other treatments, viz., zinc, and control across the measured variables (p < 0.05). Therefore, it is concluded that the application of boron at 500 ppm was found to be effective in enhancing plant growth and higher fruit yield (45 fruits) of black nightshade

Screening Bambara Groundnut (Vigna subterranea L. Verdc) Genotypes for Drought Tolerance at the Germination Stage under Simulated Drought Conditions

Bambara groundnut (Vigna subterranean L. Verdc) is grown by smallholders and subsistence farmers in the marginal parts of sub-Saharan Africa. This legume is native to Africa and is cultivated throughout semi-arid sub-Saharan Africa. It is hardy and has been recognized as a nutritious food source in times of scarcity. Drought can negatively affect the germination or establishment of seedlings in the early stages of crop growth. Drought can limit the growing season of certain crops and create conditions that encourage the invasion of insects and diseases. Drought can also lead to a lack of crop yield, leading to rising food prices, shortages, and possibly malnutrition in vulnerable populations. A drought-tolerant genotype can be identified at the germination stage of Bambara groundnut by screening for drought-tolerance traits, and this knowledge can be applied to Bambara crop improvement programs to identify drought-tolerant traits during early growth phases. As an osmolyte, polyethylene glycol (PEG 6000) reduced water potential and simulated drought stress in Bambara groundnut seeds of different genotypes. Osmolytes are low-molecular-weight organic compounds that influence biological fluid properties. In this study, 24 Bambara groundnut genotypes were used. Data were collected on seed germination percentage (G%), germination velocity index (GVI), mean germination time (MGT), root dry mass (RDM), root fresh mass (RFM), and seven drought tolerance indices: mean productivity (MP), tolerance index (TOL), geometric mean productivity (GMP), stress susceptibility index (SSI), yield index (YI), yield stability index (YSI), stress tolerance index (STI) as well as seed coat color measurements. The data were applied to the mean observation of genotypes under simulated drought conditions (Ys) and the mean observation of genotypes under controlled conditions (Yp). Germination%, germination velocity index (GVI), mass germination time (MGT), and root fresh mass (RFM) differed significantly (p &lt; 0.001) between the two stress conditions. Bambara genotypes Acc 82 and Acc 96 were found to be the most drought-tolerant

Phenotypic Variability of Root System Architecture Traits for Drought Tolerance among Accessions of Citron Watermelon (Citrullus lanatus var. citroides (L.H. Bailey)

Citron watermelon (Citrullus lanatus var. citroides) is a drought-tolerant cucurbit crop widely grown in sub-Saharan Africa in arid and semi-arid environments. The species is a C3 xerophyte used for multiple purposes, including intercropping with maize, and has a deep taproot system. The deep taproot system plays a key role in the species&rsquo; adaptation to dry conditions. Understanding the root system development of this crop could be useful to identify traits for breeding water-use efficient and drought-tolerant varieties. This study compared the root system architecture of citron watermelon accessions under water-stress conditions. Nine selected and drought-tolerant citron watermelon accessions were grown under non-stress (NS) and water stress (WS) conditions using the root rhizotron procedure in a glasshouse. The following root system architecture (RSA) traits were measured: root system width (RSW), root system depth (RSD), convex hull area (CHA), total root length (TRL), root branch count (RBC), total root volume (TRV), leaf area (LA), leaf number (LN), first seminal root length (FSRL), seminal root angle (SRA), root dry mass (RDM), shoot dry mass (SDM), root&ndash;shoot mass ratio (RSM), root mass ratio (RMR), shoot mass ratio (SMR) and root tissue density (RTD). The data collected on RSA traits were subjected to an analysis of variance (ANOVA), correlation and principal component analyses. ANOVA revealed a significant (p &lt; 0.05) accession &times; water stress interaction effect for studied RSA traits. Under WS, RDM exhibited significant and positive correlations with RSM (r = 0.65), RMR (r = 0.66), RSD (r = 0.66), TRL (r = 0.60), RBC (r = 0.72), FSRL (r = 0.73) and LN (r = 0.70). The principal component analysis revealed high loading scores for the following RSA traits: RSW (0.89), RSD (0.97), TRL (0.99), TRV (0.90), TRL (0.99), RMR (0.96) and RDM (0.76). In conclusion, the study has shown that the identified RSA traits could be useful in crop improvement programmes for citron watermelon genotypes with enhanced drought adaptation for improved yield performance under drought-prone environments

Use Patterns, Knowledge Diversity and Drivers for the Cultivation of the Miracle Plant [<i>Synsepalum dulcificum</i> (Schumach & Thonn.) Daniell] in Benin and Ghana

Despite the growing interest in the miracle plant worldwide due to its numerous applications, the threats and the wild harvest of the species hamper its sustainable utilisation. Moreover, traditional knowledge so far documented on the species is limited to a narrow geographical coverage of its natural distribution range, which is West and Central Africa. This study analysed the use variation and knowledge acquisition pattern of the miracle plant among West African sociolinguistic groups and deciphered the drivers of populations’ willingness and readiness to engage in cultivating the species. Semi-structured interviews were conducted with 510 respondents purposively selected from nine sociolinguistic groups in Benin and Ghana using the snowball sampling approach. Information was collected on respondents’ socio-demographic profile, miracle plant ownership, plant parts used and preparation methods, knowledge of the species bioecology, perceived threats on the species, willingness to cultivate, maximum acreage to allocate to the species and maximum price to pay for a seedling. Descriptive statistics, generalized linear models, classification and regression tree models were used for data analysis. The miracle plant ownership mode depended on the age category. Sociolinguistic affiliation, level of schooling, migratory status and religion significantly affected the number of trees owned. We recorded 76 uses belonging to six use categories. The overall use-value of the miracle plant significantly varied according to the respondent sociolinguistic affiliation, main activity and religion. Men were the main source of knowledge and knowledge is mainly acquired along the family line. Knowledge related to food and social uses was mostly acquired from parents and people of the same generation, while magico-therapeutic and medicinal use-related knowledge were inherited from parents and grandparents. Sociolinguistic affiliation, awareness of taboos and market availability were the most important drivers of respondent willingness to cultivate the miracle plant. While the respondent’s level of schooling and perception of plant growth rate determined the maximum acreage they were willing to allocate to the species in cultivation schemes, their main activity, sociolinguistic affiliation and knowledge of the species time to fruiting drove the maximum purchase price they were willing to offer for a seedling of the species. Our findings provide key information for the promotion of miracle plant cultivation in the study area