Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Studying photosynthetic antenna complexes in vivo and in vitro using time-resolved fluorescence spectroscopy
Ranjbar Choubeh, Reza - \ 2018
Wageningen University. Promotor(en): Herbert van Amerongen; Paul Struik. - Wageningen : Wageningen University - ISBN 9789463434959 - 182
Nodal farmers' motivations for exchanging sorghum seeds in northwestern Ethiopia
Rodier, Christophe ; Struik, Paul C. - \ 2018
Sustainability 10 (2018)10. - ISSN 2071-1050
Human capital - Motivations - Nodal farmers - Seed social network analysis - Social capital - Sorghum seeds

One of the main challenges of Ethiopian agriculture is the shortage of certified seeds of improved varieties, which results in uneven dispersal of quality seed amongst farmers. In a context where 80% to 90% of the seed requirement is covered by the informal seed sector, understanding how and why seeds are exchanged through informal channels is crucial. This study aims to describe why nodal farmers disseminate seeds at a higher rate than other farmers in their network. Following a social network analysis, in-depth surveys were conducted with identified nodal and connector sorghum farmers in order to determine the main social characteristics that differentiate them from other farmers in a western lowlands community of the Tigray Region of Ethiopia. We examined empirically the main factors that motivate them, the main drawbacks they experience, and the behavioral decisions that could potentially speed up or slow down the adoption of newly released improved varieties of sorghum. The study showed that, in this district, few significant socio-demographic differences exist between nodal and non-nodal farmers. The seed exchange network was hyper localized, as the majority of exchanges took place within village boundaries. Focus group discussions showed that a nodal position should not be taken for granted, as the network is dynamic and in constant evolution. In-depth interviews revealed that it was unlikely for accessing farmers to be consistently denied seeds due to a deeply rooted social norm insisting that one should not, under any circumstances, be turned down when asking for seeds. However, in practice, chronic seed insecure farmers suffering from poor performances may find themselves unable to access quality seeds, as automatic support should not be assumed. In terms of motivation, nodal farmers ranked maintaining friendships and relationships as the two most important. Thus, beyond the risk-sharing mechanism underlying much of the seed exchange, it is a mix of personal and community interests that motivates nodal farmers to have more exchange partners and thus disseminate more seeds on average than other farmers in the seed networks. This indicates that their social capital is the major driver to exchange seeds.

Embracing 3D Complexity in Leaf Carbon–Water Exchange
Earles, J.M. ; Buckley, Thomas N. ; Brodersen, Craig R. ; Busch, Florian A. ; Cano, F.J. ; Choat, Brendan ; Evans, John R. ; Farquhar, Graham D. ; Harwood, Richard ; Huynh, Minh ; John, Grace P. ; Miller, Megan L. ; Rockwell, Fulton E. ; Sack, Lawren ; Scoffoni, Christine ; Struik, Paul C. ; Wu, Alex ; Yin, Xinyou ; Barbour, Margaret M. - \ 2018
Trends in Plant Science (2018). - ISSN 1360-1385 - 10 p.
3D - leaf anatomy - leaf hydraulic conductance - mesophyll conductance - photosynthesis

Leaves are a nexus for the exchange of water, carbon, and energy between terrestrial plants and the atmosphere. Research in recent decades has highlighted the critical importance of the underlying biophysical and anatomical determinants of CO2 and H2O transport, but a quantitative understanding of how detailed 3D leaf anatomy mediates within-leaf transport has been hindered by the lack of a consensus framework for analyzing or simulating transport and its spatial and temporal dynamics realistically, and by the difficulty of measuring within-leaf transport at the appropriate scales. We discuss how recent technological advancements now make a spatially explicit 3D leaf analysis possible, through new imaging and modeling tools that will allow us to address long-standing questions related to plant carbon–water exchange.

Observational characterization of the Synoptic and Mesoscale circulations in Relation to Crop Dynamics: Belg 2017 in the Gamo Highlands, Ethiopia
Minda, T.T. ; Molen, M.K. van der; Heusinkveld, B.G. ; Struik, P.C. ; Vilà-Guerau de Arellano, J. - \ 2018
Atmosphere 9 (2018)10. - ISSN 2073-4433 - 24 p.
The Gamo Highlands in Ethiopia are characterized by complex topography and lakes. These modulate the mesoscale and synoptic scale weather systems. In this study, we analyzed the temporal and spatial variations in weather as function of topography and season and their impact on potato crop growth. To determine how crop growth varies with elevation, we installed a network of six automatic weather stations along two transects. It covers a 30-km radius and 1800-m elevation difference. We conducted a potato field experiment near the weather stations. We used the weather observations as input for a crop model, GECROS. Data analysis showed large differences between weather in February and May. February is more dominated by mesoscale circulations. The averaged February diurnal patter shows a strong east to southeast lake breezes and, at night, weak localized flows driven by mountain density flows. In contrast, in May, the synoptic flow dominates, interacting with the mesoscale flows. The GECROS model satisfactorily predicted the elevational gradient in crop yield. Model sensitivity experiments showed that belg-averaged precipitation distribution gave the highest yield, followed by exchanging May weather observations with April.
Impact of Positive Selection on Incidence of Different Viruses During Multiple Generations of Potato Seed Tubers in Uganda
Priegnitz, Uta ; Lommen, Willemien J.M. ; Vlugt, René A.A. van der; Struik, Paul C. - \ 2018
Potato Research (2018). - ISSN 0014-3065 - 30 p.
Multi-seasonal trials - Positive selection - Seed degeneration - Seed potatoes - Seed regeneration - Uganda - Viruses

Smallholder farmers in Uganda commonly use seed potato tubers from the informal sector, especially by seed recycling over several generations. Therefore, seed tubers are highly degenerated with viruses and other pathogens, resulting in poor yield and quality of the produce. Over one cycle of multiplication, degeneration management by positive seed selection was found to be efficient in reducing virus diseases compared with the farmers’ method of selection. The objective of this study was to assess to what extent positive selection over several seasons can reduce six different virus incidences in seed lots of different starting quality in southwestern Uganda. Multi-seasonal trials were carried out in three locations, with five seed lots from four sources and three cultivars. Detection of viruses was based on DAS-ELISA and Luminex xMAP technology. Analysis was carried out with analysis of variance (ANOVA) on angular-transformed percentages of virus incidence. Results showed fluctuations in some viruses over seasons with lower Potato leafroll virus (PLRV) and Potato virus X (PVX) incidences in lots from positive selection compared with lots from farmers’ selection. In contrast, some seed lots were initially highly infected with Potato virus S (PVS) and Potato virus M (PVM) and showed no reduction in virus incidence through positive selection. In general, little infection with Potato virus Y (PVY) and Potato virus A (PVA) was found. Based on these results, it is recommended that smallholder farmers are trained in positive selection to opt for less virus-infected plants and tubers, thus increasing potato production.

Traditional leafy vegetables in Zimbabwe: agronomic and market studies
Dube, Praxedis - \ 2018
University. Promotor(en): Wim Heijman; Paul Struik, co-promotor(en): Rico Ihle. - Wageningen : Wageningen University - ISBN 9789463435000 - 220
Reflections on the potential of virtual citizen science platforms to address collective action challenges : Lessons and implications for future research
Leeuwis, Cees ; Cieslik, K.J. ; Aarts, M.N.C. ; Dewulf, A.R.P.J. ; Ludwig, F. ; Werners, S.E. ; Struik, P.C. - \ 2018
NJAS Wageningen Journal of Life Sciences 86-87 (2018). - ISSN 1573-5214 - p. 146 - 157.
Action research - Agricultural development - Citizen science - Collective action - Connective action - Environmental observatories - ICT - Public goods

Rural communities in Africa are facing numerous challenges related to human health, agricultural production, water scarcity and service delivery. Addressing such challenges requires effective collective action and coordination among stakeholders, which often prove difficult to achieve. Against the background of the increased availability of information and communication technologies (ICTs), this article synthesizes the lessons from six case-studies reported in this Special Issue. The cases investigate the possible role of digital citizen science platforms (labelled EVOCAs: Environmental Virtual Observatories for Connective Action) in overcoming the challenges of integrating heterogeneous actors in collective management of common resources and/or the provision of public goods. Inspired by the seminal work of Elinor Ostrom, our expectation was that such platforms could help operationalize communication and information-related design principles and community conditions that are known to enhance the capacity to address environmental challenges. This article presents some cross-cutting insights and reflections regarding the nature of the challenges identified by the diagnostic studies, and on the relevance and significance of Ostrom's framework and analysis. It also reflects on the plausibility of our original ideas and assumptions by assessing what the various studies tell us about the significance and potential of key components of an EVOCA-type intervention: i.e. environmental monitoring, ICT, connective action, citizen science and responsible design. At the same time, we draw lessons for follow-up research and action in our research program and beyond by identifying several issues and themes that merit further investigation. Based on the case-studies, we conclude that many collective action challenges are of a more complex nature than originally anticipated, and often cannot be resolved within clearly demarcated communities. While this complicates the realization of Ostrom's communication and information-related design principles and community features, there may still be a meaningful role for digital citizen science platforms. To help address complex challenges, they must be oriented towards fostering adaptive and systemic learning across interdependent stakeholder communities, rather than focusing on the self-betterment of the communities alone. Such digital platforms need to be developed in a responsible manner that ensures complementarity with already existing patterns of communication and ICT-use, that anticipates dynamics of trust and distrust among interdependent stakeholders, and that prevents typical problems associated with the sharing of information such as privacy infringement and undesirable control over information by outsiders.

Towards resilience through systems-based plant breeding. A review
Lammerts van Bueren, Edith T. ; Struik, Paul C. ; Eekeren, Nick van; Nuijten, Edwin - \ 2018
Agronomy for Sustainable Development 38 (2018)5. - ISSN 1774-0746
Agrobiodiversity - Breeding strategies - Common good - Ecological resilience - Entrepreneurial models - Resource use efficiency - Seed systems - Social justice - Societal resilience - Sustainability

How the growing world population can feed itself is a crucial, multi-dimensional problem that goes beyond sustainable development. Crop production will be affected by many changes in its climatic, agronomic, economic, and societal contexts. Therefore, breeders are challenged to produce cultivars that strengthen both ecological and societal resilience by striving for six international sustainability targets: food security, safety and quality; food and seed sovereignty; social justice; agrobiodiversity; ecosystem services; and climate robustness. Against this background, we review the state of the art in plant breeding by distinguishing four paradigmatic orientations that currently co-exist: community-based breeding, ecosystem-based breeding, trait-based breeding, and corporate-based breeding, analyzing differences among these orientations. Our main findings are: (1) all four orientations have significant value but none alone will achieve all six sustainability targets; (2) therefore, an overarching approach is needed: “systems-based breeding,” an orientation with the potential to synergize the strengths of the ways of thinking in the current paradigmatic orientations; (3) achieving that requires specific knowledge development and integration, a multitude of suitable breeding strategies and tools, and entrepreneurship, but also a change in attitude based on corporate responsibility, circular economy and true-cost accounting, and fair and green policies. We conclude that systems-based breeding can create strong interactions between all system components. While seeds are part of the common good and the basis of agrobiodiversity, a diversity in breeding approaches, based on different entrepreneurial approaches, can also be considered part of the required agrobiodiversity. To enable systems-based breeding to play a major role in creating sustainable agriculture, a shared sense of urgency is needed to realize the required changes in breeding approaches, institutions, regulations and protocols. Based on this concept of systems-based breeding, there are opportunities for breeders to play an active role in the development of an ecologically and societally resilient, sustainable agriculture.

Addressing socio-ecological development challenges in the digital age : Exploring the potential of Environmental Virtual Observatories for Connective Action (EVOCA)
Cieslik, K.J. ; Leeuwis, C. ; Dewulf, A.R.P.J. ; Lie, R. ; Werners, S.E. ; Wessel, M. van; Feindt, P. ; Struik, P.C. - \ 2018
NJAS Wageningen Journal of Life Sciences 86-87 (2018). - ISSN 1573-5214 - p. 2 - 11.
Citizen science - Collective action - Connective action - EVOs - ICT4D - Participatory environmental monitoring

Climate change, (a) biotic stresses and environmental degradation are adversely affecting the sustenance of farming communities in Africa. Addressing such challenges requires effective collective action and coordination among stakeholders, which often prove difficult to achieve. Timely and context-specific information on relevant environmental dynamics holds considerable promise to overcome these problems. This paper investigates the role of citizen science in facilitating knowledge co-creation and sharing between academia, development actors and users in developing country contexts. In our approach, we focus on information sharing platforms (known as Environmental Virtual Observatories, EVOs) and their potential to facilitate adaptive decision-making in six rural case-study areas in Africa. We complement the existing theory on EVOs with a focused exploration of the connective function of ICT-enabled multi-stakeholder exchange. We propose that increased connectivity may enable new forms of collective action (labelled ‘connective action’), relevant to addressing socio-ecological challenges. Along these lines, this paper presents the theoretical and conceptual grounding of a research program that aspires to develop Environmental Virtual Observatories for Connective Action (EVOCAs) and to explore their potential for improved crop, water, livestock and disease management in rural Africa.

Potatoes and livelihoods in Chencha, southern Ethiopia
Tadesse, Yenenesh ; Almekinders, Conny J.M. ; Schulte, Rogier P.O. ; Struik, Paul C. - \ 2018
NJAS Wageningen Journal of Life Sciences (2018). - ISSN 1573-5214
Agronomy - Asset - Consumption pattern - Food security - Log-linear analysis - Potato - Production - Wealth category

Potato is highly productive crop and can provide a cheap and nutritionally-rich staple food. Its potential as a cash generator and source of food is much under-utilized in many emerging economies. In this paper we study the impact of an intervention that introduced improved potato technologies in Chencha, Ethiopia on the livelihoods of smallholder farmers. We collected information through in-depth interviews in order to explore possible pathways of impact on farmers’ livelihoods; and used this information as the basis for designing a household survey. The results show changes in agronomic practices and consumption; these changes were most pronounced among wealthy farmers who participated in the intervention. Farmers used the additional income from potato in different ways: wealthier farmers improved their houses and increased their livestock, whereas poor farmers mainly invested in furniture, cooking utensils, tools and in developing small businesses like selling and buying cereals, milk and weaving products in the local markets. Some wealthy farmers, who did not participate in the project, also derived some indirect benefits from the intervention. This underscores: i) interventions that promote uniform farming technologies in themselves are not always sufficient to improve the livelihoods of poor farmers, and ii) the need to broaden the scope of interventions so as to take into account the resources available to farmers in different wealth categories, and the diversity of strategies that they employ for improving their livelihoods. Our approach allows to understand and describe the different developmental effects of a single technological intervention on the different aspects of farmers’ livelihoods.

State transitions in the cyanobacterium Synechococcus elongatus 7942 involve reversible quenching of the photosystem II core
Ranjbar Choubeh, Reza ; Wientjes, Emilie ; Struik, Paul C. ; Kirilovsky, Diana ; Amerongen, Herbert van - \ 2018
Biochimica et Biophysica Acta. B, Bioenergetics 1859 (2018)10. - ISSN 0005-2728 - p. 1059 - 1066.
Cyanobacteria - Photosystem II - State transitions - Time-resolved fluorescence spectroscopy

Cyanobacteria use chlorophyll and phycobiliproteins to harvest light. The resulting excitation energy is delivered to reaction centers (RCs), where photochemistry starts. The relative amounts of excitation energy arriving at the RCs of photosystem I (PSI) and II (PSII) depend on the spectral composition of the light. To balance the excitations in both photosystems, cyanobacteria perform state transitions to equilibrate the excitation energy. They go to state I if PSI is preferentially excited, for example after illumination with blue light (light I), and to state II after illumination with green-orange light (light II) or after dark adaptation. In this study, we performed 77-K time-resolved fluorescence spectroscopy on wild-type Synechococcus elongatus 7942 cells to measure how state transitions affect excitation energy transfer to PSI and PSII in different light conditions and to test the various models that have been proposed in literature. The time-resolved spectra show that the PSII core is quenched in state II and that this is not due to a change in excitation energy transfer from PSII to PSI (spill-over), either direct or indirect via phycobilisomes.

Genome-wide association reveals novel genomic loci controlling rice grain yield and its component traits under water-deficit stress during the reproductive stage
Kadam, Niteen N. ; Struik, Paul C. ; Rebolledo, Maria C. ; Yin, Xinyou ; Jagadish, S.V.K. - \ 2018
Journal of Experimental Botany 69 (2018)16. - ISSN 0022-0957 - p. 4017 - 4032.
A priori candidate genes - multi-locus analysis - Oryza sativa - reproductive-stage water-deficit stress - single-locus analysis - synchronized phenology

A diversity panel comprising of 296 indica rice genotypes was phenotyped under non-stress and water-deficit stress conditions during the reproductive stage in the 2013 and 2014 dry seasons (DSs) at IRRI, Philippines. We investigated the genotypic variability for grain yield, yield components, and related traits, and conducted genome-wide association studies (GWAS) using high-density 45K single nucleotide polymorphisms. We detected 38 loci in 2013 and 64 loci in 2014 for non-stress conditions and 69 loci in 2013 and 55 loci in 2014 for water-deficit stress. Desynchronized flowering time confounded grain yield and its components under water-deficit stress in the 2013 experiment. Statistically corrected grain yield and yield component values using days to flowering helped to detect 31 additional genetic loci for grain yield, its components, and the harvest index in 2013. There were few overlaps in the detected loci between years and treatments, and when compared with previous studies using the same panel, indicating the complexity of yield formation under stress. Nevertheless, our analyses provided important insights into the potential links between grain yield with seed set and assimilate partitioning. Our findings demonstrate the complex genetic architecture of yield formation and we propose exploring the genetic basis of less complex component traits as an alternative route for further yield enhancement.

Water-and nitrogen-use efficiencies of hemp (Cannabis sativa L.) based on whole-canopy measurements and modeling
Tang, Kailei ; Fracasso, Alessandra ; Struik, Paul C. ; Yin, Xinyou ; Amaducci, Stefano - \ 2018
Frontiers in Plant Science 9 (2018). - ISSN 1664-462X
Cannabis sativa L. - Canopy gas exchange - Hemp - Nitrogen use efficiency - Water use efficiency

Interest in hemp (Cannabis sativa L.) as a crop for the biobased economy is growing worldwide because hemp produces a high and valuable biomass while requiring low inputs. To understand the physiological basis of hemp’s resource-use efficiency, canopy gas exchange was assessed using a chamber technique on canopies exposed to a range of nitrogen (N) and water levels. Since canopy transpiration and carbon assimilation were very sensitive to variations in microclimate among canopy chambers, observations were adjusted for microclimatic differences using a physiological canopy model, with leaf-level parameters estimated for hemp from our previous study. Canopy photosynthetic water-use efficiency (PWUEc), defined as the ratio of gross canopy photosynthesis to canopy transpiration, ranged from 4.0 mmol CO2 (mol H2 O)−1 to 7.5 mmol CO2 (mol H2 O)−1. Canopy photosynthetic nitrogen-use efficiency (PNUEc), the ratio of the gross canopy photosynthesis to canopy leaf-N content, ranged from 0.3mol CO2 d−1 (g N)−1 to 0.7mol CO2 d−1 (g N)−1. The effect of N-input levels on PWUEc and PNUEc was largely determined by the N effect on canopy size or leaf area index (LAI), whereas the effect of water-input levels differed between short-and long-term stresses. The effect of short-term water stress was reflected by stomatal regulation. The long-term stress increased leaf senescence, decreased LAI but retained total canopy N content; however, the increased average leaf-N could not compensate for the lost LAI, leading to a decreased PNUEc. Although hemp is known as a resource-use efficient crop, its final biomass yield and nitrogen use efficiency may be restricted by water limitation during growth. Our results also suggest that crop models should take stress-induced senescence into account in addition to stomatal effects if crops experience a prolonged water stress during growth.

Nutritional water productivity of selected leafy vegetables
Nyathi, M.K. ; Halsema, G.E. Van; Beletse, Y.G. ; Annandale, J.G. ; Struik, P.C. - \ 2018
Agricultural Water Management 209 (2018). - ISSN 0378-3774 - p. 111 - 122.
African leafy vegetables - Deficit irrigation - Hidden hunger - Indigenous leafy vegetables - Irrigation regimes - Micronutrient deficiency

The major challenge affecting rural resource-poor households (RRPHs) in South Africa is deficiencies in micronutrients (iron and zinc) and vitamin A. Traditional leafy vegetables (TLVs) are dense in iron, zinc, and β-carotene concentrations. Therefore, they are deemed suitable to improve the dietary diversity of RRPHs. The main objective of this study was to assess the effect of irrigation regimes on nutritional water productivity (NWP) of selected leafy vegetables [Amaranthus cruentus (Amaranth) and Cleome gynandra (Spider flower), both TLVs, and Beta vulgaris (Swiss chard)]. Experiments were conducted under a rain shelter at the ARC-VOP, Pretoria, South Africa, during two consecutive seasons (2013/14 and 2014/15). Leafy vegetables were subjected to three irrigation regimes [well-watered (I30), moderate water stress (I50), and severe water stress (I80)]. Data collected [(aboveground biomass (AGB), aboveground edible biomass (AGEB), actual evapotranspiration, and nutrient concentrations (iron, zinc and β-carotene)] were used to calculate NWP of leafy vegetables. Swiss chard exhibited a higher portion of AGEB compared to TLVs due to its larger harvest index (0.57-0.92). Selected TLVs displayed superiority in terms of nutrient richness compared to Swiss chard, under I50. Results indicated that TLVs could provide more than the daily-recommended nutrient intake (DRNI) for vitamin A to all age groups. For iron, Spider flower could supply more than the DRNI to infants between 1 and 3 years of age, whereas for zinc, it could supply approximately 11% to this age group. However, higher micronutrient and β-carotene concentrations did not translate to superior nutritional yield (NY). Swiss chard showed higher Fe-NY and Zn-NY, whereas TLVs were rich in β-carotene-NY. Similarly, Swiss chard demonstrated the highest Fe-NWP (1090 mg m−3) and Zn-NWP (125 mg m−3), whereas Amaranth was larger in β-carotene-NWP (1799 mg m−3), under moderate water stress. These results show that there may be an opportunity to improve NWP under drought conditions. There is a need for future studies that will assess NWP for a wider range of leafy vegetables. These studies should be conducted in different locations and explore the effect of management factors (fertiliser, water stress, planting density and planting date), and soil type on NWP of micronutrients and β-carotene.

The combined effect of elevation and meteorology on potato crop dynamics : A 10-year study in the Gamo Highlands, Ethiopia
Minda, Thomas T. ; Molen, M.K. van der; Struik, Paul C. ; Combe, Marie ; Jiménez, Pedro A. ; Khan, Muhammad S. ; Arellano, Jordi Vilà Guerau de - \ 2018
Agricultural and Forest Meteorology 262 (2018). - ISSN 0168-1923 - p. 166 - 177.
Complex terrain - High-resolution agrometeorological model - Inter-annual variability

Potato (Solanum tuberosum L.) is an important crop in the Gamo Highlands in Ethiopia. The region is characterised by a complex topography with large inter-annual weather variations, where potatoes grow in a range of altitudes between 1,600 and 3,200 m above sea level (a.s.l.). Traditional large-scale crop modelling studies only crudely represent the effect of complex topography, misrepresenting spatial variability in meteorology and potato growth in the region. Here, we investigate how weather influenced by topography affects crop growth. We used the Weather Research and Forecasting (WRF) model to simulate weather in relation to topography in coarse (54 km × 54 km) and fine (2 km × 2 km) resolution domains. The first has a resolution similar to those used by large-scale crop modelling studies that only crudely resolve the horizontal and vertical spatial effects of topography. The second realistically represents the most important topographical variations. The weather variables modelled in both the coarse and fine resolution domains are given as input to the GECROS model (Genotype-by-Environment interaction on CROp growth Simulator) to simulate the potato growth. We modelled potato growth from 2001 to 2010 and studied its inter-annual variability. This enabled us to determine for the first time in Ethiopia how variations in weather are linked to crop dynamics as a function of elevation at a fine resolution. We found that due to its finer representation of topography, weather and crop growth spatio-temporal variations were better represented in the fine than in the coarse resolution domain. The magnitude of crop growth variables such as Leaf Area Index (LAI) and Length of the Growing Season (LGS) obtained with weather from the coarse resolution domain were unrealistically low, hence unacceptable. Nevertheless, the resulting potato yields in the coarse resolution domain were comparable with the yields from the fine resolution domain. We explain this paradoxical finding in terms of a compensating effect, as the opposite effects of temperature and precipitation on yield compensated for each other along the major potato growing transect in the Gamo Highlands. These offsetting effects were also dependent on the correct estimations of the LGS, LAI. We conclude that a well-resolved representation of complex topography is crucial to realistically model meteorology and crop physiology in tropical mountainous areas.

Perspectives of children orphaned by HIV/AIDS on ecology and gathering of wild orchids in Tanzania
Challe, Joyce F.X. ; Struik, Paul C. ; Price, Lisa L. - \ 2018
Journal of Ethnobiology 38 (2018)2. - ISSN 0278-0771 - p. 223 - 243.
children orphaned by HIV/AIDS - edible orchids - gathering knowledge acquisition - local ecological knowledge - orchid conservation

Orchid gathering in the Southern Highlands of Tanzania became an income generating strategy for HIV/AIDS-affected households, particularly for children orphaned by HIV/AIDS. Being orphaned might have implications for children's local ecological knowledge leading to indiscriminate harvesting of both preferred and non-preferred orchids. Using qualitative and quantitative mixed methods, we assessed the knowledge of wild orchid species among gatherers in four categories: Children orphaned by HIV/AIDS, children not affected by HIV/AIDS, HIV/AIDS-affected adults, and non-HIV/AIDS-affected adults. Data collection took place from February 2006 until February 2007. More than 70% of the children orphaned by HIV/AIDS relied on tuber taste and texture to distinguish preferred and non-preferred species. HIV/AIDS-affected adults were competent at using orchid morphology to distinguish preferred from non-preferred orchid species. Gatherers stated preferred orchid species were primarily found in restricted areas, and non-preferred species were widespread. Cramer's V analysis revealed an association between the HIV/AIDS status of a gatherer and the gatherer's views on the conservation status of preferred and non-preferred species. Gatherers perceived non-preferred species as having higher natural regeneration potential than preferred species. Cramer's V analysis also showed a difference in gathering knowledge acquisition between HIV/AIDS-affected double orphans who emigrated from urban settings, and those residing in their natal rural village under guardian care. Both types of orphans relied primarily on other children for gathering knowledge, but those with guardians also gleaned knowledge from guardians. Across categories, children also gained knowledge from middlemen, who buy and resell the preferred orchids.

Reducing damping-off problems in eggplant (Solanum melongena L.) : A participatory testing of nursery management in Bangladesh
Nahar, Naznin ; Islam, Md Rashidul ; Uddin, Mohammad Mahir ; Jong, Peter de; Struik, Paul C. ; Stomph, Tjeerd Jan - \ 2018
Crop Protection 112 (2018). - ISSN 0261-2194 - p. 177 - 186.
Damping-off - Healthy seedlings - Integrated pest management - Seed treatment - Soil treatment - Source of pathogens

Eggplant seedling production in homestead nurseries of farmers in Jamalpur (Bangladesh) is greatly compromised by damping-off. Therefore, farmers often do not have enough seedlings to transplant. Effective treatments of soil and seed to reduce disease pressure in the nurseries are available but little is known on the relative contributions of soil-borne and seed-borne pathogens to damping-off and on how nursery management can integrate management options under farmers’ conditions. A 2-year nursery study was conducted in consecutive seasons, jointly with farmers and using farmers’ preserved seed and farmers’ nurseries subject to damping-off problems. Year 1 involved a single nursery, Year 2 nine nurseries. The following treatments were tested: Trichoderma harzianum as soil amendment combined with seed treatment using either hot water or Carbendazim and farmers’ conventional practice: curative spraying after appearance of damping-off. In Year 1, a control (no intervention) treatment was also included. Emergence of seedlings, incidence of damping-off, seedling performance variables and farmers’ appreciation of seedling vigour were recorded. Soil treatment with T. harzianum combined with seed treatment with hot water increased seedling emergence and produced 25–64 percentage points more healthy seedlings than farmers’ conventional practice. This combined treatment also improved seedling performance (height, root length, lateral root development), and reduced stem girdling, a symptom associated with disease infection of transplants. To determine the contributions of nursery soil and farmers’ seed to damping-off, blotter and in vitro studies in the laboratory and tray studies in a screen house were performed. Soil proved to be the major pathogen source and treating nursery soil with T. harzianum had the largest positive effect on seedling performance, both reducing damping-off and enhancing seedling growth.

Roles of nitrogen and cytokinin signals in root and shoot communications in maximizing of plant productivity and their agronomic applications
Gu, Junfei ; Li, Zhikang ; Mao, Yiqi ; Struik, Paul C. ; Zhang, Hao ; Liu, Lijun ; Wang, Zhiqin ; Yang, Jianchang - \ 2018
Plant Science 274 (2018). - ISSN 0168-9452 - p. 320 - 331.
Cytokinin transport - Long-distance signaling - Nitrogen status - Root - shoot relationship - Source-sink relationship

Nitrogen is an essential, often limiting, factor in plant growth and development. To regulate growth under limited nitrogen supply, plants sense the internal and external nitrogen status, and coordinate various metabolic processes and developmental programs accordingly. This coordination requires the transmission of various signaling molecules that move across the entire plant. Cytokinins, phytohormones derived from adenine and synthesized in various parts of the plant, are considered major local and long-distance messengers. Cytokinin metabolism and signaling are closely associated with nitrogen availability. They are systemically transported via the vasculature from plant roots to shoots, and vice versa, thereby coordinating shoot and root development. Tight linkage exists between the nitrogen signaling network and cytokinins during diverse developmental and physiological processes. However, the cytokinin-nitrogen interactions and the communication systems involved in sensing rhizospheric nitrogen status and in regulating canopy development remain obscure. We review current knowledge on cytokinin biosynthesis, transport and signaling, nitrogen acquisition, metabolism and signaling, and their interactive roles in regulating root-shoot morphological and physiological characteristics. We also discuss the role of spatio-temporal regulation of cytokinins in enhancing beneficial crop traits of yield and nitrogen use efficiency.

Calibration and validation of the AquaCrop model for repeatedly harvested leafy vegetables grown under different irrigation regimes
Nyathi, M.K. ; Halsema, G.E. van; Annandale, J.G. ; Struik, P.C. - \ 2018
Agricultural Water Management 208 (2018). - ISSN 0378-3774 - p. 107 - 119.
Biomass - Crop modelling - Evapotranspiration, indigenous leafy vegetables - Water productivity

Traditional leafy vegetables (TLVs’) are vegetables that were introduced in an area a long time ago, where they adapted to local conditions and became part of the local culture. In Sub-Saharan Africa, the use of TLVs’ as a nutrient dense alternative food source to combat micronutrient deficiency of rural resource-poor households (RRPHs), has gained attention in debates on food and nutrition security. However, TLVs’ are underutilised because of lack of information on their yield response to water and fertiliser. To better assess TLVs’ yield response to water stress, the AquaCrop model was calibrated (using 2013/14 data) and validated (using 2014/15 data) for three repeatedly harvested leafy vegetables [Amaranthus cruentus (Amaranth), Cleome gynandra (Spider flower), and Beta vulgaris (Swiss chard)] in Pretoria, South Africa. Experiments were conducted during two consecutive seasons, in which the selected leafy vegetables were subjected to two irrigation regimes; well-watered (I30) and severe water stress (I80). Measured parameters were canopy cover (CC), soil water content (SWC), aboveground biomass (AGB), actual evapotranspiration (ETa), and water productivity (WP). Statistical indicators [root mean square error (RMSE), RMSE-standard deviation ratio (RSR), R2, and relative deviation] showed good fit between measured and simulated (0.60 < R2 < 0.99, 0.94 < RMSE < 5.44, and 0.04 < RSR < 0.79) values for the well-watered treatment. However, the fit was not as good for the water-stressed treatment for CC, SWC, ETa and WP. Nevertheless, the model simulated the selected parameters satisfactorily. These results revealed that there was a clear difference between transpiration water productivity (WPTr) for C4 crops (Amaranth and Spider flower) and a C3 crop (Swiss chard); WPTr for the C4 crops ranged from 4.61 to 6.86 kg m−3, whereas for the C3 crop, WPTr ranged from 3.11 to 4.43 kg m−3. It is a challenge to simulate yield response of repeatedly harvested leafy vegetables because the model cannot run sequential harvests at one time; therefore, each harvest needs to be simulated separately, making it cumbersome. To design sustainable food production systems that are health-driven and inclusive of RRPHs, we recommend that more vegetables (including traditional vegetables) should be included in the model database, and that sequential harvesting be facilitated.

Plant responses to elevated CO2 and the need to go deeper
Struik, Paul - \ 2018
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