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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Making interventions work on the farm : Unravelling the gap between technology-oriented potato interventions and livelihood building in Southern Ethiopia
Tadesse, Yenenesh - \ 2017
Wageningen University. Promotor(en): P.C.. Struik, co-promotor(en): C.J.M. Almekinders; R.P.O. Schulte. - Wageningen : Wageningen University - ISBN 9789463436847 - 120
potatoes - crop production - crop physiology - technology - intervention - livelihood strategies - livelihoods - ethiopia - east africa - aardappelen - gewasproductie - gewasfysiologie - technologie - interventie - strategieën voor levensonderhoud - middelen van bestaan - ethiopië - oost-afrika

Poor adoption of modern technologies in sub-Saharan Africa is one of the major factors that limit food production and thereby threaten food security of smallholder farmers. This is despite the potential and emerging success stories of new technologies in increasing productivity of smallholder agriculture. Explanations for low uptake of technologies are diverse. Some studies associated it with characteristics of the farmers and their farm; others attributed it to poor access to information about a particular technology, while some others recognize the importance of technology attributes. Farmers’ adoption decision is shaped socially and the farming practices are changing, not only because of the technical changes introduced, but also because of changes in social circumstances among smallholders. All these possible reasons did, however, miss largely important insights on how local complexities influence adoption. The research presented in this thesis analyses the social dynamics of technology-oriented interventions. More specifically, the study assessed the influence of technology introduction strategies, social networks and social differentiation on the adoption, dissemination and effects of potato technologies. As a case, it used interventions introducing improved potato technologies in Chencha, Southern Ethiopia. The field work combined individual and group in-depth interviews, household surveys and field observation for data collection.

Results show that the efforts to introduce technologies for improved potato production to progressive farmers with the assumption that farmers will eventually adopt, once they become familiar with the technology is a distant prospect. Some of the production practices - agronomic field and storage practices - failed to spread to poor farmers as expected, while the majority of agronomic practices fitted well with wealthy farmers. This resulted in diverse outcomes and strategies for livelihood improvement at household level. Access to the technologies and the necessary resources and diverse needs for technology were important factors in explaining variation in adoption and effects of technology across wealth categories. Tracing the seed diffusion through farmers’ networks showed that not all households had equal access to improved seed potatoes, mainly because of social barriers formed by differences in wealth, gender and religion, and because the type of personal relationship (relatives, neighbours, friends and acquaintance) between seed providers and seed recipients affected farmer to farmer seed sharing. In addition, the set-up of farmer-group based seed production demands resources and faces contextual challenges, which could be addressed through a long-term approach that engages continually in diagnosis and responding to the emerging social as well as material challenges. Development practitioners, however, took organizing group initiatives as a one-time process of design and start-up activity. Thus, clean seed potato production and dissemination through farmers’ organizations could not be sustainable. In conclusion, the present study has indicated that through providing special attention to the social dynamics researchers can arrive at better understanding of constraints affecting technology adoption. This implies effective interventions for a range of farm contexts involve not only finding technical solutions but also integrated understanding of farmers’ production conditions and existing social dynamics.

Dynamic photosynthesis under a fluctuating environment: a modelling-based analysis
Morales Sierra, Alejandro - \ 2017
Wageningen University. Promotor(en): Paul Struik; Jaap Molenaar, co-promotor(en): Xinyou Yin; Jeremy Harbinson. - Wageningen : Wageningen University - ISBN 9789463430456 - 282
photosynthesis - modeling - analysis - environmental factors - light - canopy - leaves - crop physiology - metabolism - fotosynthese - modelleren - analyse - milieufactoren - licht - kroondak - bladeren - gewasfysiologie - metabolisme

In their natural environment, leaves are exposed to rapid fluctuations of irradiance. Research on CO2 assimilation under fluctuating irradiance often relies on measurements of gas exchange during transients where irradiance is rapidly increased or decreased, after the leaf has adapted to a particular set of environmental conditions. In the field, such increases and decreases occur mostly because of sunflecks (rapid increases in irradiance on a low irradiance background) created by gaps in the canopy and plant movement by wind, and cloudflecks (rapid decreases in irradiance on a high irradiance background) generated by clouds that transiently block the sun.

In this dissertation, the metabolic regulation of photosynthesis and how this may limit dynamic CO2 assimilation is studied in silico with the development and application of simulation models. In order to support the development of the models, a review of the literature was performed as well as an experiment designed to generate data on dynamic CO2 assimilation for different photosynthetic mutants of Arabidopsis thaliana. In addition to providing these models to the research community, this dissertation also identifies multiple targets that may be used for improving dynamic CO2 assimilation in plants. It further demonstrates that the dynamic responses of CO2 assimilation to changes in irradiance has a significant effect on canopy CO2 assimilation, even for dense canopies exposed to open skies, resembling the conditions of commercial crops.

In Chapter 1, the context of this dissertation is presented. The societal relevance of this research is argued, making reference to the role that photosynthesis could play in addressing global problems such as food and energy security. The necessary background on the physiology of photosynthesis is provided, with special emphasis on the terminology and concepts required to understand the rest of the dissertation, with the aim of making the contents more accessible to a wider audience. Then, prior literature on the specific topics of this dissertation (i.e., photosynthesis in a dynamic environment and its mathematical modelling) is presented, with a chronological approach that analyses the evolution of ideas and methodologies up to the present.

In Chapter 2, the current literature on dynamic CO2 assimilation is reviewed, with an emphasis on the effects of environmental conditions ([CO2], temperature, and air humidity) on the rates of photosynthetic induction and loss of induction. This review reveals major knowledge gaps, especially on the loss of induction. The little data available indicates that rates of photosynthetic induction increase with [CO2], which could be explained by a weak effect on Rubisco activation and a strong effect on stomatal opening. Increases in temperature also increase the rates of photosynthetic induction, up to an optimum, beyond which a strong negative effect can be observed, which could be attributed to deactivation of Rubisco activase.

In Chapter 3, an experiment is presented that makes use of several photosynthetic mutants of A. thaliana. Downregulating non-photochemical quenching and sucrose synthesis did not have any significant effect on dynamic CO2 assimilation, whereas CO2 diffusion and Rubisco activation exerted stronger limitations. Further analysis reveals that whether stomatal opening limits CO2 assimilation after an increase in irradiance depends on the stomatal conductance prior to the change in irradiance. A threshold value of 0.12 mol m−2 s−1 (defined for fluxes of water vapour) could be defined, above which stomata did not affect the rates of photosynthetic induction. The comparison of measurements across irradiance levels also indicated that the apparent rate constant of Rubisco activation is irradiance-dependent, at least for irradiance levels below 150 μmol m−2 s−1.

In Chapter 4, a phenomenological model of leaf-level CO2 assimilation is presented. The model is described in detail and all the parameters are first estimated with published data, and later refined by fitting the model to the data from Chapter 3. Additional data from the experiment in Chapter 3 is used to validate predictions of CO2 assimilation under lightflecks for the different photosynthetic mutants. The model predicts accurately dynamic CO2 assimilation for the different photosynthetic mutants by only modifying those parameters that are affected by the mutation. This demonstrates that the model has a high predictive power and that the equations, although phenomenological in nature, have a solid physiological basis.

The model is further used to analyse, in silico, the limitations imposed by different photosynthetic processes on dynamic CO2 assimilation at the leaf and canopy level, allowing a more in depth analysis than in Chapter 3. The analysis demonstrates that results obtained at the leaf level should not be extrapolated directly to the canopy level, as the spatial and temporal distribution of irradiance within a canopy is more complex than what is achieved in experimental protocols. Both at the leaf and canopy level, CO2 diffusion is strongly limiting, followed by photoinhibition, chloroplast movements and Rubisco activation.

In Chapter 5, a mechanistic model of the dynamic, metabolic regulation of the electron transport chain is presented. The model is described in detail and all the parameters are estimated from published literature, using measurements on A. thaliana when available. Predictions of the model are tested with steady-state and dynamic measurements of gas exchange, chlorophyll fluorescence and absorbance spectroscopy on A. thaliana, with success.

The analysis in silico indicates that a significant amount of alternative electron transport is required to couple ATP and NADPH production and demand, and most of it is associated with nitrogen assimilation and export of redox power through the malate shuttle. The analysis also reveals that the relationship between ATP synthesis and the proton motive force is highly regulated by the concentrations of substrates (ADP, ATP and inorganic phosphate), and this regulation facilitates an increase in non-photochemical quenching under conditions of low metabolic activity in the stroma.

In Chapter 6, the findings of Chapters 2–5 are summarised and employed to answer in detail the four research questions formulated in Chapter 1. Of great interest is the identification of six potential targets that may be used to improve dynamic CO2 assimilation. These targets are: (i) regulation of Rubisco activity through changes in the amount or regulation of Rubisco activase, (ii) acceleration of stomatal opening and closure, (iii) a lower /ATP for ATP synthesis, (iv) faster relaxation of non-photochemical quenching, (v) reduced chloroplast movements, and (vi) reduced photoinhibition by increased rates of repair of Photosystem II.

Nitrogen use efficiency in potato : an integrated agronomic, physiological and genetic approach
Ospina Nieto, C.A. - \ 2016
Wageningen University. Promotor(en): P.C. Struik; E. Lammerts Van Bueren, co-promotor(en): C.G. van der Linden. - Wageningen : Wageningen University - ISBN 9789462576469 - 177
solanum tuberosum - potatoes - nitrogen - nutrient use efficiency - plant breeding - crop physiology - plant physiology - quantitative trait loci - cultivars - solanum tuberosum - aardappelen - stikstof - nutriëntengebruiksefficiëntie - plantenveredeling - gewasfysiologie - plantenfysiologie - loci voor kwantitatief kenmerk - cultivars

Nitrogen (N) fertilizers increased food production over the last 60 years, but also contributed significantly to the use of fossil energy and the total amount of reactive N in the environment. Agriculture needs to reduce N input and increase nitrogen use efficiency (NUE). Legislation like the Nitrate Directive (91/767/EEC) and the Water Framework Directive (2000/60/EC) forces a reduction in N supply in crop production. The effects of this constraint on yield and quality of potato are expected to be significant since N plays an important role in the vegetative development and production of potato. Considerable amounts of N are needed as N recovery is notoriously low due to the small and shallow roots. The overall aim of this thesis is to improve the nitrogen use efficiency of potato under low nitrogen supply. Specific aims are i) to understand the N effects on potato performance, especially under low N input, ii) to quantify the genotypic variation under contrasting N inputs, iii) to identify quantitative trait loci associated with the crop’s response to nitrogen. We used ecophysiological models to dissect the canopy development into biological meaningful parameters as phenotyping tools. Two potato populations (a set of tetraploid cultivars and a biparental diploid population) were phenotyped in the field under two contrasting N levels. Additionally, a set of 6 cultivars from three maturity groups (early, middle and late) were phenotyped in more detail under 5 nitrogen conditions combining two input levels and two fertilizers types plus a control without nitrogen fertilisation. The curve-fit parameters were, together with other agronomical traits, used in the agronomic and genetic analysis. Our approach using the ecophysiological models captured the phenotypic response to N, enhancing the interpretation of the nitrogen effects and of the differences among maturity types. The nitrogen effects on canopy development resulted in large differences in light interception, tuber yield, tuber size distribution and nitrogen uptake. There were differences in the response to nitrogen between the diploid biparental population and the set of tetraploid cultivars. In general, in the diploid population, having less vigour and therefore less potential to respond to the extra nitrogen, the time required to complete each phase of the canopy development was longer than in the set of tetraploids. In the set of cultivars the rate of early vegetative growth was higher, the onset of the phase with maximum canopy cover was earlier, and the duration of maximum canopy was longer than for the diploid population. However, in both the diploid and the tetraploid population maturity was the major factor accounting for genetic variation in canopy development and tuber development traits. The genotypic differences were reflected in quantitative trait loci that were either N dependent or N independent, with pleiotropic regions affecting most of the maturity-related traits. Few traits showed quantitative trait loci on common regions that were not maturity related like those on chromosomes 2 and 6 (association mapping) or linkage groups ma_VI, pa_VIII pa_XI. Maturity obscures other genotype-dependent physiological traits; therefore it is imperative to find traits that are responsible for genotypic variation, but not related to maturity type. Moreover the results showed that nitrogen use efficiency under low nitrogen input is higher than under high nitrogen input, and higher for late cultivars than for early cultivars. Therefore, breeding for nitrogen use efficiency under low input requires direct selection combined with good response to extra nitrogen and should be done within each maturity group. Finally in a broader context we discussed the need of high-throughput phenotyping in breeding for complex traits, like those involving efficiency, to make the most of the large amount of genetic data, all possible based on advances in technology in remote sensing and images analysis.

Keywords: Association mapping, Breeding for low input, Canopy development, Maturity type, Nitrogen use efficiency, Potato, Solanum tuberosum, Quantitative trait loci.

Stuurlicht in de Glastuinbouw : 1. Kansen voor energiebesparing?
Dueck, T.A. ; Hogewoning, S. ; Pot, S. ; Meinen, E. ; Trouwborst, G. ; Kempkes, F.L.K. - \ 2015
Bleiswijk : Wageningen UR Glastuinbouw (Rapport GTB 1349) - 56
teelt onder bescherming - gewasproductie - gewasopbrengst - gewaskwaliteit - gewasfysiologie - kunstlicht - kunstmatige verlichting - plantenfysiologie - aanvullend licht - blauw licht - verrood licht - rood licht - phalaenopsis - kalanchoe - chrysanten - protected cultivation - crop production - crop yield - crop quality - crop physiology - artificial light - artificial lighting - plant physiology - supplementary light - blue light - far red light - red light - chrysanthemums
This report focusses on energy efficient steering light applications by energy efficient lighting systems, but especially with new possibilities to influence crop growth and production with the light spectrum. After an introduction of the physiological background and application of steering light, new applications for steering light in the future are described with respect to energy saving opportunities. Possible scenario’s for steering light are presented for phalaenopsis, chrysanthemum and kalanchoë.
Improving radiation use efficiency in greenhouse production systems
Li, Tao - \ 2015
Wageningen University. Promotor(en): Leo Marcelis, co-promotor(en): Ep Heuvelink. - Wageningen : Wageningen University - ISBN 9789462572577 - 156
glastuinbouw - kassen - gewasfysiologie - agrarische productiesystemen - gewasproductie - stralingsbenuttigingsefficiëntie - straling - fotosynthese - licht - gebruiksefficiëntie - greenhouse horticulture - greenhouses - crop physiology - agricultural production systems - crop production - radiation use efficiency - radiation - photosynthesis - light - use efficiency


A large increase in agricultural production is needed to feed the increasing world population with their increasing demand per capita. However, growing competition for arable land, water, energy, and the degradation of the environment impose challenges to improve crop production. Hence agricultural production efficiency needs to increase. Greenhouses provide the possibility to create optimal growth conditions for crops, thereby improving production and product quality. Light is the driving force for plant photosynthesis and in greenhouse horticulture, light is often the most limiting factor for plant growth. Therefore, improving radiation use efficiency (RUE) in greenhouse production systems is imperative in order to improve plant growth and production. The objective of this thesis is to obtain insight in improving RUE in greenhouse production systems through better understanding of crop physiology. Three aspects related to RUE have been studied in this thesis, 1) improving light distribution in the crop canopy; 2) allowing more light in the greenhouse during summer; and 3) balancing the source and sink strength during plant growth.

Light is heterogeneously distributed in the crop canopy. Due to the saturating response of leaf photosynthesis rate to light, a more homogeneous light distribution in the canopy will result in a higher crop photosynthesis. In Chapter 2, the effect of diffuse glass on spatial light distribution in a fully developed tomato canopy and its direct and indirect effects on crop photosynthesis were explored. Diffuse glass, which transforms a portion of direct solar light into diffuse light without influencing the light transmissivity of the glass, was applied as greenhouse cover. Under diffuse glass cover, light was more evenly distributed (in both horizontal and vertical direction) within the canopy compared with plants grown under conventional clear glass cover. Besides a more uniform light distribution, diffuse glass also resulted in higher leaf photosynthetic capacity in the middle of the crop canopy and in a higher leaf area index (LAI). The higher leaf photosynthetic capacity was positively correlated with a higher leaf total nitrogen and chlorophyll content. Moreover, lower leaf temperature and less photo-inhibition of top canopy leaves were observed under diffuse glass cover when global radiation was high. Total crop photosynthesis between 1st April and 1st October was enhanced by 7.2 % under diffuse glass. This enhancement mainly resulted from four factors (in order of decreasing importance): a more homogeneous horizontal light distribution, a higher leaf photosynthetic capacity, a more uniform vertical light distribution and a higher LAI.

In summer growers of shade tolerant pot-plants often apply shading screens in the greenhouse or white wash on the greenhouse cover in order to avoid leaf or flower damage caused by high light. Shading carries a penalty on potential crop growth which is positively related to the amount of light that can be captured. Considering the advantageous properties of diffuse glass cover, i.e. a more homogeneous light distribution, a lower leaf temperature and less photo-inhibition when global radiation is high, in Chapter 3 we tested the feasibility of allowing more light (i.e. less shading) via diffuse glass cover for cultivation of shade tolerant pot-plants during summer. Two Anthurium andreanum cultivars (Pink Champion and Royal Champion) were grown in 3 greenhouse compartments. Under similar DLI [7.5 mol m-2 d-1 PAR (photosynthetic active radiation)], diffuse glass cover resulted in 8 % higher crop RUE (i.e. dry mass production per unit intercepted light) in ‘Royal Champion’ compared with clear glass cover treatment, which consequently resulted in higher total biomass production. This effect was not observed in ‘Pink Champion’. Under diffuse glass cover, high DLI (10 mol m-2 d-1 PAR) resulted in 20-23 % higher total biomass production in both cultivars compared with low DLI (7.5 mol m-2 d-1 PAR), this mainly resulted from the higher cumulative intercepted light. No flower or leaf damage was observed in these treatments. High DLI even resulted in more compact plants as indicated by a higher ratio of aboveground fresh mass to plant height.

In Chapter 4, we addressed a question resulting from Chapter 3, i.e. why the stimulating effect of diffuse light on crop RUE in anthurium pot-plants is cultivar specific? We excluded the fraction of canopy light interception and steady-state leaf photosynthesis as potential explanations, and explained it from instantaneous leaf photosynthesis which closely correlates with the temporal light distribution. Diffuse glass cover smoothed the variation of temporal light distribution at a given point on a leaf during a clear day, which consequently resulted in less temporal variation of stomatal conductance in ‘Royal Champion’ which had stomata showing a fast-response to the variation in light intensity. As stomata are the gateway for CO2 uptake, less variation in stomatal conductance imposed less limitation for leaf photosynthesis under diffuse glass cover, thereby resulting in a higher crop RUE. For ‘Pink Champion’, however, stomata were less responding to variations in light intensity. Therefore, stomata imposed only a marginal limitation on leaf photosynthesis even under clear glass cover where the temporal incident light intensity varied substantially due to the shadow cast by the greenhouse construction parts and equipment.

Application of supplementary assimilation light in greenhouses is rapidly increasing. The beneficial effect of supplementary assimilation light is determined by the balance between assimilate production in source leaves and the overall capacity of the plant to use these assimilates. Therefore, it is important to identify the source-sink balance during plant growth. In Chapter 5, three tomato cultivars with different potential fruit size [‘Komeett’ (large size); ‘Capricia’ (medium size); ‘Sunstream’ (small size, cherry tomato)] were grown under commercial crop management. We estimated the source-sink ratio from the early growth stage to fully fruiting stage through experimentation and model simulation. Carbohydrate content of leaves and stems were periodically determined. Tomato plants showed a period of sink limitation (‘Komeett’ and ‘Capricia’) or came close to sink limitation (‘Sunstream’) during the early growth stage under ample natural irradiance (early September) as indicated by a source-sink ratio higher than or close to 1. Fruiting tomato plants were source-limited as indicated by an extremely low source-sink ratio (average source-sink ratio from 50 days after planting onwards was 0.17, 0.22 and 0.33 for ‘Komeett’, ‘Capricia’ and ‘Sunstream’, respectively). During the fully fruiting stage, the source-sink ratio was negatively correlated with the potential fruit size when commercial fruit load was maintained. Carbohydrate content in tomato stems and leaves increased linearly with plant source-sink ratio.

The experiments and results described in this thesis provide insights for improving RUE in greenhouse production systems. The main achievements and limitations as well as practical applications are discussed in Chapter 6.

Modelling concept of lettuce breeding for nutrient efficiency
Kerbiriou, P.J. ; Stomph, T.J. ; Lammerts Van Bueren, E. ; Struik, P.C. - \ 2014
Euphytica 199 (2014)1-2. - ISSN 0014-2336 - p. 167 - 181.
nitrate concentration - root architecture - systems biology - crop physiology - water - nitrogen - growth - plants - availability - experiences
Modern lettuce cultivars are bred for use under high levels of input of water and nutrients, and therefore less adapted to low-input or organic conditions in which nitrate availability varies over time and within the soil profile. To create robust cultivars it is necessary to assess which traits contribute to optimal resource capture and maximum resource use efficiency. We therefore revisited earlier published results on root growth, resource capture and resource use efficiency of lettuce exposed to localized drought and nitrate shortage in a pot experiment. Root growth in a soil profile with localized resource shortage depended on the resource that was in short supply. We conceptualized a model describing nitrogen uptake and use efficiency. We also investigated the genetic variation among 148 cultivars in resource capture over time and soil depth and in resource use efficiency in four (two locations × two planting dates) field experiments. Cultivars proved to be highly diverse in their ability to capture and use resources. This ability, however, was strongly affected by other sources of variance, stressing the need for an eco-physiological model capable of reducing the residual variance and improving the expression and evaluation of cultivar differences in relation to both resource capture and use efficiency in lettuce. We showed that genetic variation was best expressed under limiting conditions. To improve the conceptualized model further we identified issues requiring further analysis, e.g., the physiological reasons why certain cultivars are capable of quickly responding to changes in the environment to maintain optimal resource capture
Using agronomic tools to improve pineapple quality and its uniformity in Benin
Fassinou Hotegni, V.N. - \ 2014
Wageningen University. Promotor(en): Paul Struik; Jack van der Vorst, co-promotor(en): Willemien Lommen. - Wageningen : Wageningen University - ISBN 9789462570382 - 302
ananas comosus - ananassen - fruitteelt - gewaskwaliteit - plantmateriaal - heterogeniteit - verbetering - gewasfysiologie - benin - ananas comosus - pineapples - fruit growing - crop quality - planting stock - heterogeneity - improvement - crop physiology - benin

Keywords: Ananas comosus; Benin; cultural practices; fruit quality; hapas; heterogeneity; planting material; slips; suckers; supply chain; variation in quality; variation within crop; vigour.

Poor average quality and uniformity in quality have become major issues in agri-food chains. This is also the case in the pineapple sector in Benin where less than 2% of the fresh pineapple is exported to international markets. The average quality of pineapple delivered to other markets, local and regional, is poor. The present thesis studied the improvement options in the pineapple sector which will help pineapple producers to produce higher pineapple quality for different markets, including international ones. This thesis aimed at (1) understanding how fresh pineapple supply chains are organised in Benin and identifying the bottlenecks for delivering the right pineapple to the right market; (2) increasing our knowledge on the agronomic tools used by pineapple producers to produce pineapple fruits; (3) understanding how agronomic factors affect pineapple quality and harvesting time, and (4) proposing and discussing the trade-offs between cultural practices. Research included analysis of supply chains and cropping systems and field experimentation.

To understand how fresh pineapple supply chains are organised, 54 semi-structured interviews were held with key informants and 173 structured interviews with actor groups. Results indicated six main actor groups in the fresh pineapple chains: primary producers, exporters, wholesalers (those selling at local markets and those selling at regional markets), processors, retailers, and middlemen. Two pineapple cultivars were grown: Sugarloaf and Smooth Cayenne, with Sugarloaf being dominant in local and regional markets and Smooth Cayenne in European markets. The main constraints hampering the effectivity of the chains were: the non-controlled conditions under which the pineapple was transported from one actor group to another, the lack of appropriate storage facilities at wholesaler’s and processor’s levels, the unavailability of boxes for export and the non-concordance between actor groups in which quality attributes and criteria they valued most. In addition, most respondents interviewed affirmed that the pineapple quality was highly heterogeneous, emphasising the need to understand how pineapple is grown in Benin and what the constraints for producing high pineapple quality are.

To find out the agronomic tools in use by pineapple producers in Benin, interviews were held with 100 producers in the pineapple production areas. Pineapple production practices proved diverse for both cultivars in planting density, flowering induction practice and fertiliser application. The production systems of the two pineapple cultivars differed in planting material used (slips in cv. Sugarloaf; hapas plus suckers in cv. Smooth Cayenne); the use of K2SO4 (not commonly used in cv. Sugarloaf and commonly used in cv. Smooth Cayenne); the number of fertiliser applications (lower in cv. Sugarloaf than in cv. Smooth Cayenne) and in the maturity synchronisation practice by means of Ethephon (not commonly used in cv. Sugarloaf and commonly used in cv. Smooth Cayenne). Constraints for high quality production were the unavailability of planting material, unavailability and high costs of fertilisers and the heterogeneity in planting material weight.

To understand how agronomic factors affect pineapple quality and harvesting time, four on-farm experiments were conducted in commercial pineapple fields. Results first indicated that the heterogeneity in fruit weight was a consequence of the heterogeneity in plant vigour at artificial flowering induction time. The plant vigour at flowering induction was mainly related with the infructescence weight and less or not with crown weight. Second, results indicated that artificial flowering induction gave fruits with lower infructescence weight and heavier crown than natural flowering induction. Artificial maturity induction reduced the total soluble solids (TSS) concentration in the fruits. Finally, results showed that the reason why a high proportion of fruits in cv. Sugarloaf was not exportable to Europe was the high value in the ratio crown: infructescence height (above 1.5); in cv. Smooth Cayenne, reasons were a ratio crown: infructescence height as well as a TSS below 12 ºBrix.

To come up with improvement options for high pineapple quality production with low heterogeneity in quality, the possibility of pruning slips on selective plants as means to improve uniformity in fruit quality was evaluated through two on-farm experiments on commercial fields with cv. Sugarloaf. Results revealed that pruning of slips did not significantly improve average fruit quality attributes and was not successful in achieving more uniform fruit quality at harvesting time. Through one experiment per pineapple cultivar, we investigated how fruit quality and its variation were affected by weight (in both pineapple cultivars) and type (in cv. Smooth Cayenne only) of planting material. Results showed that fruits from heavy planting material had heavier infructescence and fruit weights, longer infructescence height, but shorter crown height and smaller ratio crown: infructescence height than those from light planting material. In cv. Sugarloaf fruits from heavy planting material had higher variation in crown weight and lower variation in infructescence height than fruits from light and mixed (light plus heavy) planting materials. In cv. Smooth Cayenne, fruits from heavy planting material had a lower variation in fruit height than fruits from other classes of planting material. The type of planting material (in cv. Smooth Cayenne) had no effect on the average fruit quality attributes except on the crown height where fruits from hapas had shorter crowns than those from suckers. The type of planting material had in overall no significant effect on the variation in the fruit quality attributes.

The present study is a step towards the improvement of the whole pineapple sector in Benin. It identified constraints for high pineapple quality production but also tested and proposed improvement options for high pineapple quality production.

Grain filling, starch degradation and feeding value of maize for ruminants
Ali, M. - \ 2013
Wageningen University. Promotor(en): Paul Struik; Wouter Hendriks, co-promotor(en): John Cone. - Wageningen : Wageningen UR - ISBN 9789461738196 - 177
maïs - zea mays - groeifasen, rijp - genotypen - zetmeelvertering - pensvertering - voedingswaarde - herkauwersvoeding - korrels (granen) - maïskuilvoer - kuilvoerbereiding - gewasfysiologie - voedingsfysiologie - maize - zea mays - maturity stage - genotypes - starch digestion - rumen digestion - nutritive value - ruminant feeding - kernels - maize silage - silage making - crop physiology - nutrition physiology

Keywords; Maize (Zea mays L), Genotypes, Grain filling, Growth temperature, Kernels, Gas production, Starch degradation, Oven-drying, Silage, Ensiling temperature, Ensiling duration, Feeding value, Lactating cows

Maize (Zea mays L.) is a major component in the ration of dairy cows in many parts of the world. The currently increasing economic importance of maize has highlighted the need to determine its nutritional value, and to assess the factors influencing its nutritive value. Genotypic make-up (especially differences in starch and endosperm), growing conditions, maturity stage at harvest, and post handling processes, like oven-drying, can influence nutritive value of maize kernels. Similarly, ensiling temperature and duration can affect feeding value of maize silage. This thesis is divided into three parts; the first aim was to characterize the dry matter (starch) accumulation of maize different genotypes in different environments under controlled (glasshouse) and on different locations (sand and clay) in field conditions. Maize genotypes used were different in starch structure and composition, and in type of endosperm. Starch structure refers to amylose and amylopectin; and composition refers to their proportions, whereas type of endosperm defines levels of vitreousness. The vitreousness is the ratio of vitreous (hard) to floury (soft) endosperm. Six maize genotypes, differing in amylose content and vitreousness, were grown under three contrasting day/night temperature regimes during grain filling and harvested at different maturity stages from two greenhouse experiments. Similar investigations were carried on another set of genotypes grown on sandy and clay soils and with different sowing times under field conditions. Water contents and dry matter (starch) accumulation were significantly influenced by growth temperature, genotype, soil type and sowing time (P<0.0001). The second aim of thesis was to establish a relationship between rumen in vitro starch degradation (feeding value) of maize kernels and different factors, like genotype, growth temperature during grain filling, and maturity stage. Oven-dried kernels of six maize genotypes, from the two greenhouse experiments mentioned before were investigated. Starch content was measured using an enzymatic method and the gas production technique was used to assess starch degradation in rumen fluid of dairy cows. The extent of starch degradation at different incubation times was calculated from measured gas production data (6, 12 and 20 h, respectively) and a published equation. At each maturity stage, whole kernel and starch degradation in rumen fluid depended on the genotype (P<0.0001), growing conditions (P<0.0001), starch content (P<0.0001) and starch amount (P<0.0001) in the kernels. The same but fresh (not oven-dried) maize kernel samples were investigated using gas production technique to determine the impact of oven-drying on rumen in vitro starch degradation of maize kernels. Oven-drying significantly (P<0.0001) influenced the rumen in vitro starch degradation in maize kernels various incubation times, with more starch being degraded in the fresh than in the oven-dried maize kernels, although the differences were small. There was a consistent and highly significant (P<0.009 to 0.0002) interaction between oven-drying and genotype, with the high-amylose genotype showing larger effects of oven-drying than the other genotypes. The third aim of thesis was to investigate effect of ensiling temperature and duration on feeding value of maize silage. Samples of maize whole plants (dry matter 33%) were collected from the medium vitreous endosperm cultivar, grown in different seasons on sandy soils. Maize plants were chopped and ensiled in mini silos at three different temperatures. Samples from the silos were taken after 0 (not ensiled, i.e. control), 4, 8 and 16 weeks of ensiling. The gas production technique was used to evaluate the influence of the ensiling temperature and duration of ensiling on the degradation of the fresh ground silage samples in rumen fluid. The final pH of the silages and the gas production was significantly influenced by ensiling temperature in both seasons (P<0.0001). Gas production and pH decreased with an increase in ensiling duration (P<0.0001). The relationship between pH and gas production was quadratic and depended on the ensiling temperature (P<0.002). It was found that ensiling temperature and ensiling duration determine the rate of change and final pH, and play a significant role in feeding value of maize silage. The finding of thesis can be used to determine the exact feeding value of maize kernels and silage, and also can be used as a tool to revise the current feeding evaluation systems i.e. shift from oven-dried to fresh samples.

Studies on agronomy and crop physiology of Plectranthus edulis (Vatke) Agnew
Taye, M. - \ 2008
Wageningen University. Promotor(en): Paul Struik, co-promotor(en): Willemien Lommen. - [S.l. : S.n. - ISBN 9789085049159 - 148
plectranthus - agronomie - agronomische kenmerken - planten met knollen - knollen - gewassen - etnobotanie - ethiopië - knolvorming - gewasfysiologie - economische botanie - nieuwe cultuurgewassen - agro-ecologie - plectranthus - agronomy - agronomic characteristics - tuberous species - tubers - crops - ethnobotany - ethiopia - tuberization - crop physiology - economic botany - new crops - agroecology

Keywords: Development, morphology, plant density, potato, radiation interception, radiation use efficiency, seed size, seed tuber, spacing, stolon, tipping, tuber

Plectranthus edulis (Vatke) Agnew (Lamiaceae) is an ancient Ethiopian tuber crop grown in mid and high altitude areas in the north, south and south-west of Ethiopia. Cultivation dates back from c. 3000 BC, but in recent years its acreage and production have declined. Renewed interest to conserve the crop and increase its production is limited by absence of accurate information on growth, development and cultural practices of P. edulis. This project aimed at providing the basic knowledge needed to direct further applied research.
A standard production technique was developed after interviewing farmers in Chencha and Wolaita in southern Ethiopia, and was used in later experiments. The standard planting material chosen were de-sprouted tuber pieces, prepared from a medium (12–15 cm) sized mother tuber broken into three pieces. Three pieces were planted per hole, at a hole spacing of 75  90 cm. Shoot tipping (pinching; the removal of the apices with 12 leaf pairs) was carried out when the crop was 10–15 cm high.
The general structure of the crop was similar to that of Irish potato. Plant components were: the seed tuber pieces, sprouts, main stems, branches, leaves, inflorescences, fruits, seeds, roots, stolons and tubers. The crop had a long growing period. In two growth studies, maximum fresh tuber yields were attained c. 34 weeks after planting (WAP). Above-ground development was characterised by a late emergence (c. 4 weeks), a slow development of the canopy after emergence until full ground cover was attained (c. 20 weeks), a very short period during which ground cover was full (c. 2 weeks) and a relative fast decline in ground cover thereafter (6−8 weeks). Primary and secondary branches constituted the major part of the canopy. The first stolons were formed c. 1012 WAP on below-ground nodes of main stems and primary branches. Tubers were first recorded at 18 WAP as a swelling on the tip of the stolon and sometimes as a swelling of the middle part of stolons. Tubers attained a maximum length of 2025 cm, and a maximum diameter of c. 2 cm. Aerial stolons were initiated 1216 weeks later than below-ground stolons and could be up to 2.5 m long.
The increase in tuber fresh weight with time was realized by an increase in both number of tubers and in average weight per tuber over the entire tuber formation period. Fresh tuber yields at 34 WAP were 4549 Mg ha1. Yield levels in other sets of experiments in which the harvest date was chosen arbitrarily were c. 21 Mg ha1 (29.7 WAP) and c. 30 Mg ha1 (34.7 WAP). Experimental yields were very high compared to those reported by farmers.
Nevertheless, in growth studies, the average daily dry matter production of the crop over the whole growing period was only 4.2−4.6 g m2 day1. The dry matter production was limited by a poor radiation interception by the canopy – only one third of the incident radiation was intercepted − and a low radiation use efficiency (RUE) – on average only 1.59 g MJ1 photosynthetically active radiation (PAR). RUE gradually increased after emergence to about 2.7 g MJ1 PAR when tuber formation was still in an early stage (24−26 WAP), but then declined because of a stagnation or decline in total crop dry weight, that lasted several weeks. Dry matter production decreased in that period because the decrease in canopy dry matter – especially stem dry matter − was not yet compensated for by the increase in tuber dry matter. This was attributed partly to a still limited capacity of the tubers to convert and / or store assimilates in this stage. Later this changed and total dry weight and RUE increased again. Harvest index was 8199% at the moment when tuber yield was maximum.
Shoot tipping significantly increased ground cover and delayed canopy senescence. Tipping also had a positive – though not always significant – effect on tuber yield. Tipping enhanced early stolon formation, but did not consistently affect the number of stolons later in the growing season
Because differences among tipped treatments were not large, limiting the tipping frequency to one will help to save time, labour and money.
Across experiments in which the number and size of the tuber pieces planted per hole were varied, the tuber fresh weight increased when the number of main stems per m2 increased up to 2.53 main stems per m2. This sufficiently high stem number could usually be achieved by planting sufficient seed tuber material (equalling at least one medium-sized mother tuber per hole) and breaking it into two or three pieces. This confers with the farmers practice. Over all treatments, an increase in fresh tuber yield was never realized by merely increasing the individual tuber weight, but either by combined effects on number of tubers and individual tuber fresh weight or by an effect on number of tubers alone.
A further increase in radiation interception by advancing and improving canopy development could likely be achieved by planting larger seed pieces, pre-sprouting the seed tuber pieces and using a higher plant density. However, the below ground development should be geared to that. At present the late initiation and formation of tubers already seems to limit production, and this should be improved when an enhanced canopy cover should result also in higher tuber yield.
On short term notice, however, the major constraints to concentrate on will be the shortage of seed tubers and the poor storability of the progeny tubers. Shortage of seed tubers was mentioned by the interviewed P. edulis farmers as a major constraint and the principle reason for the decline in production of P. edulis. The present practice by farmers of storing tubers in situ in the ground was shown to reduce tuber fresh weights by 3659% and the number of tubers by 1848% in 6 weeks.

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