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Cultivated sorghum [Sorghum bicolor (L.) Moench] is an important food security crop in the semi-arid regions of the world including Asia and Africa. Its genetic diversity is contained mostly in traditional varieties and modern cultivars used by farmers. In this study, agro-morphological traits and molecular markers were used to assess genetic diversity in 22 accessions of cultivated sorghum from five countries (Botswana, Namibia, Swaziland, Zambia and Zimbabwe) in the Southern African Development Community (SADC) region. The study revealed a significant variation among 22 accessions in both qualitative and quantitative morphological traits, indicating the accessions’ promising potential as breeding material. For molecular analysis, 11 microsatellite primer-pairs were used, and generated a total of 70 alleles across 20 accessions. Analysis of molecular variance revealed a high level of genetic variation; 67 % among the accessions and 10 % among the five countries. The patterns of genetic diversity and the relationships observed in this study should provide insights for genetic resource conservation and utilization of sorghum germplasm in the SADC region.

We report here the development of 75 SSR markers for Bambara groundnut through various sequencing approaches and the subsequent utilization of these SSR markers and other marker types (DArT Arrays) for the analysis of genetic diversity, population structure and the selection of pure lines from landraces. To assess the level of genetic diversity in Bambara groundnut landrace collections, 68 and 201 polymorphic SSR and DArT markers, respectively, were assayed against 24 single individual seed from a core collection of landraces. Polymorphic information content (PIC) ranged from 0.08 to 0.89 with an average of 0.42 across all SSR polymorphic markers, with observed (Ho) and expected (He) heterozygosity of 0.01 and 0.5 respectively. For the population structure analysis, 12 SSR markers selected as highly polymorphic from the initial screen were assayed against 123 landrace accessions. The average PIC across the 12 SSR was 0.66 with an average Ho of 0.02 and an inbreeding coefficient (f) of 0.98, suggesting that seed derived from a single plant essentially represents an unselected variety. Based on the low level of Ho and high f observed in the landrace samples, a subset of 35 genotypes derived from the landraces were advanced for field trials in Botswana and scored for 37 phenotypic traits. These 35 individual genotypes were ranked for agronomic performance based on yield component factors and other qualitative traits after field evaluation. Five genotypes with good yield potential and adaptability were recommended as potential varieties for Botswanan agro-ecology.

Sorghum is an economically important and a staple food crop for over half a billion people in developing countries, mostly in arid and semi-arid regions where drought stress is a major limiting factor. Although sorghum is generally considered tolerant, drought stress still signifcantly hampers its productivity and nutritional quality across its major cultivation areas. Hence, understanding both the efects of the stress and plant response is indispensable for improving drought tolerance of the crop. This review aimed at enhancing our understanding and provide more insights on drought tolerance in sorghum as a contribution to the development of climate resilient sorghum cultivars. We summarized fndings on the efects of drought on the growth and development of sorghum including osmotic potential that impedes germination process and embryonic structures, photosynthetic rates, and imbalance in source-sink relations that in turn afect seed flling often manifested in the form of substantial reduction in grain yield and quality. Mechanisms of sorghum response to drought-stress involving morphological, physiological, and molecular alterations are presented. We highlighted the current understanding about the genetic basis of drought tolerance in sorghum, which is important for maximizing utilization of its germplasm for development of improved cultivars. Furthermore, we discussed interactions of drought with other abiotic stresses and biotic factors, which may increase the vulnerability of the crop or enhance its tolerance to drought stress. Based on the research reviewed in this article, it appears possible to develop locally adapted cultivars of sorghum that are drought tolerant and nutrient rich using modern plant breeding techniques.

Purpose This field study evaluated the interactive effects of biochar (BC) and sewage sludge (SS) on P bioavailability and spinach yields for two seasons.

Method Treatments were combinations of biochar (0, 2.5 and 5 Mg ha-1 ) and sewage sludge (0, 6 and 12 Mg ha-1 ), or mineral fertilizer (200, 28, and 18.9 kg ha-1 ), amended in a randomized complete block design to Luvisol and Cambisol.

Results Significant (p < 0.05) yield increase of 53 and 65%, respectively occurred with increasing sole biochar doses on the Luvisol. Both applied alone and in combination with BC, the high rate of SS increased (p < 0.05) yields on the Luvisol over two seasons. Complimentary effects of 6SS+5BC on the Luvisol showed the highest yield increase for the study period. Co-application of amendments on the Cambisol decreased (p > 0.05) yields compared to sole amendments. Mehlich – 3 extractable P (M3-P) in control plots (CONT) increased between seasons, presumably due to P inputs from the irrigation water. Co-amendments on the Cambisol resulted in higher M3-P increase over mineral fertilizer than on the Luvisol in both seasons. Accumulation of M3-P in control plots confounded correlations between crop yields and available P. Higher P under BC compared to SS amended soils emphasize biochar capacity to capture P from irrigation water.

Conclusion The results suggest that combined low rates of SS and BC can have significant effects on P availability and crop yields. Biochar enhanced plant P uptake, but decrease in yields with simultaneous increase in M3-P between seasons warrants further research.

The article presents results of a survey conducted in the northern part of Botswana. The study was designed to assess the quantity of vegetable produced, production trend and constraints faced by farmers. The survey was done at Ditladi and Gulushabe in the farmer’s fields in May 2019 using a pre-tested survey questionnaire. Farmers were interviewed individually in their farms. Vegetable production and importation data was sourced from Horticultural sector and department of agricultural business promotion. Farmers (41.18%) perceived an upward production trend but data from agricultural offices indicate that production is fluctuating while generally low in all crops except cabbage. Farmers are faced with constraints such as gullies that limit the cultivable area, lack of implements, and lack of transport. The small size of fields is a bottleneck to most farmers. Prevalence of crop pests and diseases results in heavy application of synthetic chemicals. Cropping plan is neglected by more than half of the farmers interviewed. Farmers do not utilize available programs and financiers satisfactorily. They interact with government extension agents mostly on quarterly basis and are aware of climate change at the same time experiencing its consequences. There is a need for a joint effort for on-farm trials and information dissemination by the relevant stakeholders.

A total of 170 bambara groundnut (Vigna subterranea) accessions were evaluated using both simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers generated using genotyping-by-sequencing (GbS), of which 56 accessions were collected from West and East Java. Principal coordinate analysis (PCoA), population structure, and cluster analysis suggest that the East Java accessions could be a result of the introduction of selected West Java accessions. In addition, the current Indonesian accessions were likely introduced from Southern Africa, which would have produced a very marked founding effect such that these accessions present only a fraction of the genetic variability that exists within this species.

Crop resilience and yield stability are complex traits essential for food security. Sorghum bicolor is an important grain crop that shows promise for its natural resilience to drought and potential for marginal land production. We have developed sorghum lines in the Tx430 genetic background suppressed for MSH1 expression as a means of inducing de novo epigenetic variation, and have used these materials to evaluate changes in plant growth vigor. Plant crossing and selection in two distinct environments revealed features of phenotypic plasticity derived from MSH1 manipulation. Introduction of an epigenetic variation to an isogenic sorghum population, in the absence of selection, resulted in 10% yield increase under ideal field conditions and 20% increase under extreme low nitrogen conditions. However, incorporation of early-stage selection amplified these outcomes to 36% yield increase under ideal conditions and 64% increase under marginal field conditions. Interestingly, the best outcomes were derived by selecting mid-range performance early-generation lines rather than highest performing. Data also suggested that phenotypic plasticity derived from the epigenetic variation was nonuniform in its response to environmental variability but served to reduce genotype × environment interaction. The MSH1-derived growth vigor appeared to be associated with enhanced seedling root growth and altered expression of auxin response pathways, and plants showed evidence of cold tolerance, features consistent with observations made previously in Arabidopsis. These data imply that the MSH1 system is conserved across plant species, pointing to the value of parallel model plant studies to help devise effective plant selection strategies for epigenetic breeding in multiple crops.

The effects of biochar and sewage sludge application on spinach (Spinacia oleracea L.) yield and soil NO3 - content were investigated in typical soils of Botswana (Luvisol, Cambisol) under field conditions. Ten treatments with 3 levels of biochar (0, 2.5, 5 tons ha-1 ) and sewage sludge (0, 6, 12 ton ha-1 ) were applied in 2 subsequent seasons. Significant (p < 0.05) yield increase on the Luvisol occurred if sewage sludge was added at 12 Mg ha-1 with or without biochar. A combination of 6 Mg ha-1 sludge and 5 Mg ha-1 biochar application resulted in the highest crop yield over 2 seasons. On the Cambisol, only marginal yield increase occurred upon high rates of sole organic amendments and chemical fertilizer, while coapplications decreased yields. Decrease in soil NO3 - content caused yield declines in the second season, while P uptake increased significantly (p < 0.05). Correlations between yields, soil NO3 - and leaf N contents were insignificant (p > 0.05). On the Cambisol, a significant regression model for sludge and soil NO3 - was determined. Therefore, one – time combined application of 6 Mg ha-1 sewage sludge and 5 Mg ha-1 on the Luvisol, and 12 Mg ha-1 sewage sludge are recommended for spinach production on the Luvisol and Cambisol, respectively. In subsequent seasons, crop productivity could be maintained by application of mineral N in order to mitigate over-application of P.

Biochar can influence bioavailability of micronutrients and crop yields in sewage sludge-treated soils, but the mechanisms of its effects remain poorly understood. Therefore, this field experiment was conducted on a Luvisol and Cambisol to investigate the bioavailability and uptake of some micronutrients and spinach (Spinacia oleracea L.) yields grown in soil amended with biochar and sewage sludge. Ten treatments arranged in randomized complete block design with three levels of biochar (0, 2.5, 5 t/ha) and sewage sludge (0, 6, 12 t/ha) and combinations thereof were applied. High rate of sole sewage sludge, and its combination with biochar significantly (p < 0.05) increased yield on the Luvisol. On the Cambisol, only marginal yield increase resulted from high rates of sole organic amendments and chemical fertilizer, while co-applications decreased yields. Co-amendments generally increased bioavailability of micronutrients relative to sole amendments in the order Fe > Cu = Zn, with greater increase on the Cambisol, but uptake of micronutrients decreased with co-application rates of amendments. Contents of micronutrients in plant leaves were within the normal range, except for a combination of highest dosage of co-amendments on the Cambisol (Fe; 560 mg/kg), which resulted in leaf necrosis and 7% yield depression. The results showed greater yield response of spinach to co-application of amendments on the Luvisol.

Common bean (Phaseolus vulgaris L.) is a vital source of nutrients worldwide. It is one of the most consumed grain legume in Botswana. Fourteen Andean common bean genotypes were evaluated in four environments (two seasons and two diverse agro-ecologies) to determine the effect of genotype and environment interaction and yield stability. The genotypes were grown in a randomized complete block design with three replications. Grain yield data was analyzed on additive main effects and multiplicative interaction (AMMI), cultivar superiority index, Wricke’s ecovalence and Finlay and Wilkinson regression. There was a lack of variation among the selected genotypes, while environment and genotype × environment interaction (GEI) was significant (P <0.01), which is an opportunity to select stable genotypes across environments. AMMI model for total variation revealed that the environment effect was dominant at 36.83%, genotype × environment interaction at 19.82%, while genotype alone was 3.38%. The cumulative sum of squares of the first two interaction principal component axes (IPCAs) accounted for 76.13% of interaction. Stability coefficients consistently identified genotypes DAB494, CAL96 and DAB541 as the most stable and well adapted, besides the low yield realized. These genotypes are useful for stability breeding purposes and for introduction to the semi-arid environment of Botswana.