Paper I – A blueprint for applying circular economy principles to the sisal supply chain in Tanzania Page 82 The purpose of this research was to develop a blueprint for applying circular economy principles to agribusiness supply chains, using life cycle assessment (LCA) as a screening tool to assess a wide range of environmental impacts. A nutrient balance of sisal production was undertaken to quantify the extent of depletion of the nutrients calcium, potassium, nitrogen, magnesium and phosphorus in the soil in current industry practice. Potential savings in land area required for sisal production of 25-47% were calculated using yield differences reported in literature. A circular economy assessment within Tanzania identified the national waste streams with the most potential to address the nutrient depletion issue. The authors modelled the anaerobic digestion process of these streams as cosubstrates with sisal processing waste, subsequent biogas production and its use for electricity production substituting electricity consumption from the Tanzanian grid, using Life cycle assessment (LCA) to assess and compare the scenarios. Results indicated that if the cosubstrates have no current beneficial use, then the beef manure and marine fish processing wastes were the best cosubstrates, whereas if the cosubstrates have a beneficial reuse as fertiliser, then the marine fish processing wastes and human urine are the best cosubstrates. The processes with the largest contributions to environmental impact in the modelled systems were offset national electricity production and the onsite waste management (anaerobic digestion and biogas combustion). The authors concluded that there is significant potential to improve the sustainability of Tanzanian sisal production, using waste recycling from within the Tanzanian economy.

/pdf/global-integration-model-for-life-cycle-assessment-in-small-3t56pnx1ja.pdf

Global integration model for Life Cycle Assessment in Small and Medium Sized Enterprises (SME)

Nutrient depletion in Tanzanian sisal production has led to yield decreases over time. We use nutrient mass balances embedded within a life cycle assessment to quantify the extent of nutrient depletion for different production systems, and then used circular economy principles to identify potential cosubstrates from within the Tanzanian economy to anaerobically digest with sisal wastes. The biogas produced was then used to generate bioelectricity and the digestate residual can be used as a fertilizer to address the nutrient depletion. Life cycle assessment was used in a gate-to-gate assessment of the anaerobic digestion options with different cosubstrates. If no current beneficial use of the cosubstrate was assumed, then beef manure and marine fish processing waste were the best cosubstrates. If agricultural wastes were assumed to have a current beneficial use as fertilizer, then marine fish processing waste and human urine were the best cosubstrates. The largest reduction in environmental impacts resulted from bioelectricity replacing electricity from fossil fuels in the national electricity grid and improved onsite waste management practices. There is significant potential to revitalize Tanzanian sisal production by applying circular economy principles to sisal waste management to address soil nutrient depletion and co-produce bioenergy.

/pdf/addressing-nutrient-depletion-in-tanzanian-sisal-fiber-mtepnvnxi9.pdf

Addressing Nutrient Depletion in Tanzanian Sisal Fiber Production Using Life Cycle Assessment and Circular Economy Principles, with Bioenergy Co-Production

Sisal purple leafroll disease (SPLD) is aÂ destructive disease affecting sisal inÂ China, however, its etiology remains unknown. This disease is characterized byÂ purple margins and rolling and yellowing ofÂ the leaves. Recently, phytoplasma was found toÂ be present inÂ SPLD-affected sisal according toÂ PCR assay. ToÂ further verify the presence ofÂ phytoplasma, determine its association with SPLD and identify the possible pathogenic phytoplasma infecting sisal, 80 symptomatic and 65 asymptomatic sisal samples were collected from the main sisal farms inÂ three Chinese provinces, including Hainan, Guangdong and Guangxi provinces, from 2018 toÂ 2021. PCR assays and transmission electron microscopy further revealed the presence ofÂ phytoplasma. Nested PCR using the universal primer R16mF2/R16mR1 followed byÂ R16F2n/R16R2 was confirmed asÂ the most effective molecular method for the detection ofÂ phytoplasma inÂ sisal. AÂ comparison ofÂ the detection rate ofÂ phytoplasma inÂ symptomatic (83%) versus asymptomatic (17%) sisal populations showed some association between phytoplasma and SPLD. Sequencing analyses, phylogenetic analyses, and virtual restriction fragment length polymorphism analyses confirmed the presence ofÂ phytoplasma inÂ sisal belonging toÂ 16SrI-B. This is the first report ofÂ 16SrI-B phytoplasma infecting sisal inÂ China. 

/pdf/detection-and-molecular-identification-of-a-16sri-group-30mi5pw7.pdf

Detection and molecular identification of a 16SrI group phytoplasma associated with sisal purple leafroll disease

Sisal purple leafroll disease (SPLD) is currently the most destructive disease affecting sisal in China, yet its aetiology remains unclear. In our previous research, it was verified to be associated with phytoplasmas, and nested PCR based on the 16S rRNA gene using universal primers R16mF2/R16mR1 followed by R16F2n/R16R2 was confirmed as the most effective molecular method for the detection of phytoplasmas associated with SPLD (SPLDaP). However, the method has a shortcoming of inaccuracy, for it could produce false positive results. To further manage the disease, accurate detection is needed. In this study, we developed a specific nested PCR assay using universal primers R16F2n/R16R2, followed by a set of primers designed on 16Sr gene sequences amplified from SPLDaP, nontarget bacteria from sisal plants, and other phytoplasma subgroups or groups. This established method is accurate, specific, and effective for detection of 16SrI group phytoplasma in sisal, and its sensitivity is up to 10 fg/μL of total DNA. It also minimized the false positive problem of nested PCR using universal primers R16mF2/R16mR1 followed by R16F2n/R16R2. This method was further used to verify the presence of phytoplasma in Dysmicoccus neobrevipes, and the results showed that D. neobrevipes could be infected by SPLDaP and thus could be a candidate for vector transmission assays.

/pdf/development-of-a-specific-nested-pcr-assay-for-the-detection-j1qmhas0.pdf

Development of a Specific Nested PCR Assay for the Detection of 16SrI Group Phytoplasmas Associated with Sisal Purple Leafroll Disease in Sisal Plants and Mealybugs

Leaf samples from healthy and diseased sisal plants and the corresponding topsoil samples were analysed. The results show that K deficiency is the main cause of ‘banding disease’, whereas manganese is probably involved in ‘purple leaf tip roll’.



For healthy growth, the important factors are good content of organic matter, pH 6–7 and a well balanced uptake of nutrients with no excess of one or more elements.

A. Muller

Papers

Health status of sisal plants (Agave sisalana) as related to soils and the mineral composition of their leaves