Fertilisers differentially affect facultative and obligate parasitic weeds of rice and only occasionally improve yields in infested fields

Different fertilisers were field tested to investigate whether they (1) suppress the obligate parasitic weed Striga asiatica and the facultative parasitic weed Rhamphicarpa fistulosa, and (2) favour rainfed rice yields under parasitic weed infestation. Four years of experiments were conducted in southwest Tanzania, in a S. asiatica-infested rainfed upland and a R. fistulosa-infested rainfed lowland field. Treatments included sole mineral (NPK or Di-Ammonium Phosphate —DAP— plus urea), organic (cattle manure or rice husk), combinations of mineral and organic fertilisers and a no-fertiliser control. Fertilisers moderately suppressed the obligate parasite S. asiatica, but no correlations between infestation level and soil fertility status were observed. In the lowland field, fertilisers promoted the facultative R. fistulosa, in particular the ones that included organic components. Plant-available phosphorus, exchangeable potassium and soil organic matter content correlated with R. fistulosa infestation levels. Positive fertiliser effects on yields were found in both parasitic weed infested fields, except in years with high S. asiatica infestation levels. Rice husks alone and rice husks or manure combined with DAP and urea increased yields and soil fertility most. We conclude that fertilisation differentially affects the obligate and facultative parasitic weeds of rice systems; obligate parasites may be slightly suppressed, but facultative parasites may even be stimulated. Meanwhile, consistent rice yield increases under parasitic weed infested conditions cannot be obtained with fertiliser application when parasitic weed infestation levels are too high

Systems approaches to innovation in pest management: reflections and lessons learned from an integrated research program on parasitic weeds in rice

This paper provides a retrospective look at a systems-oriented research program, on the increasing occurrence of parasitic weeds in rainfed rice in sub-Saharan Africa, to qualitatively assess merits and identify challenges of such approach. We gained a broad contextual overview of the problem and different stakeholders' roles, which enabled identification of entry points for innovations in parasitic weed management. At the crop level parasitic weed infestation is associated with poor soil fertility and water management. Farmers' infrequent use of inputs to control them was caused by various factors, ranging from fears of undesired side effects (agronomic) to a lack of quality control of products (institutional). Furthermore, there may be enough extension agents, but they lack the required training on (parasitic) weed management to provide farmers with advice, while their organizations do not provide them with the necessary means for farm visits. At even higher organizational levels we observed a lack of coherent policies on parasitic weed control and implementation of them. Merits and challenges of an integrated multi-stakeholder and multi-level research project are discussed

RAAIS: Rapid Appraisal of Agricultural Innovation Systems (Part I). A diagnostic tool for integrated analysis of complex problems and innovation capacity

This paper introduces Rapid Appraisal of Agricultural Innovation Systems (RAAIS). RAAIS is a diagnostic tool that can guide the analysis of complex agricultural problems and innovation capacity of the agricultural system in which the complex agricultural problem is embedded. RAAIS focuses on the integrated analysis of different dimensions of problems (e.g. biophysical, technological, socio-cultural, economic, institutional and political), interactions across different levels (e.g. national, regional, local), and the constraints and interests of different stakeholder groups (farmers, government, researchers, etc.). Innovation capacity in the agricultural system is studied by analysing (1) constraints within the institutional, sectoral and technological subsystems of the agricultural system, and (2) the existence and performance of the agricultural innovation support system. RAAIS combines multiple qualitative and quantitative methods, and insider (stakeholders) and outsider (researchers) analyses which allow for critical triangulation and validation of the gathered data. Such an analysis can provide specific entry points for innovations to address the complex agricultural problem under study, and generic entry points for innovation related to strengthening the innovation capacity of agricultural system and the functioning of the agricultural innovation support system. The application of RAAIS to analyse parasitic weed problems in the rice sector, conducted in Tanzania and Benin, demonstrates the potential of the diagnostic tool and provides recommendations for its further development and use

Genetic variation in strigolactone production and tillering in rice and its effect on Striga hermonthica infection

Tillering in cereals is a complex process in the regulation of which also signals from the roots in the form of strigolactones play an important role. The strigolactones are signalling molecules that are secreted into the rhizosphere where they act as germination stimulants for root parasitic plants and hyphal branching factors for arbuscular mycorrhizal fungi. On the other hand, they are also transported from the roots to the shoot where they inhibit tillering or branching. In the present study, the genetic variation in strigolactone production and tillering phenotype was studied in twenty rice varieties collected from all over the world and correlated with S. hermonthica infection. Rice cultivars like IAC 165, IAC 1246, Gangweondo and Kinko produced high amounts of the strigolactones orobanchol, 2′-epi-5-deoxystrigol and three methoxy-5-deoxystrigol isomers and displayed low amounts of tillers. These varieties induced high S. hermonthica germination, attachment, emergence as well as dry biomass. In contrast, rice cultivars such as Super Basmati, TN 1, Anakila and Agee displayed high tillering in combination with low production of the aforementioned strigolactones. These varieties induced only low S. hermonthica germination, attachment, emergence and dry biomass. Statistical analysis across all the varieties confirmed a positive correlation between strigolactone production and S. hermonthica infection and a negative relationship with tillering. These results show that genetic variation in tillering capacity is the result of genetic variation in strigolactone production and hence could be a helpful tool in selecting rice cultivars that are less susceptible to S. hermonthica infection

Systems approaches to innovation in crop protection. A systematic literature review

The objective of this paper is to explore the extent to which systems approaches to innovation are reflected in the crop protection literature and how such approaches are used. A systematic literature review is conducted to study the relation between crop protection and systems approaches to innovation in 107 publications. The analysis of the crop protection literature demonstrates that only a small fraction is systems-oriented as compared to the bulk of publications with a technology-oriented approach. The analysis of agricultural innovations systems literature shows that, although crop protection is addressed, the potential of this systems approach remains largely unexplored for crop protection innovation. A large share of the publications included in this review focus on cropping or farming ‘systems’ while ‘innovation’ often equals the development, transfer, adoption and diffusion of crop protection technologies at farm level. There is relatively little attention for the institutional and political dimensions of crop protection and the interactions between farm, regional and national levels in crop protection systems. The traditional division of roles and responsibilities of researchers as innovators, extension personnel as disseminators, and farmers as end-users, is challenged only to a limited extent. The majority of publications discusses ways to optimise existing features of crop protection systems, without exploring more structural transformations that may be required to enhance the resilience of crop protection systems

RAAIS: Rapid Appraisal of Agricultural Innovation Systems (Part II). Integrated analysis of parasitic weed problems in rice in Tanzania

Parasitic weeds such as Striga spp and Rhamphicarpa fistulosa in smallholder rice production systems form an increasing problem for food and income security in sub-Saharan Africa. In this paper we implement the Rapid Appraisal of Agricultural Innovation Systems (RAAIS) as a diagnostic tool to identify specific and generic entry points for innovations to address parasitic weeds in rain-fed rice production in Tanzania. Data were gathered across three study sites in Tanzania where parasitic weeds are eminent (Kyela, Songea Rural and Morogoro Rural districts). The results demonstrate that in Tanzania, weeds in general and parasitic weeds in particular receive little attention in agricultural research, training and education curricula. Crop protection policies mainly focus on the control of (insect) pest and diseases and there is relatively little attention for weed prevention, which is essential for addressing parasitic weed problems effectively. Specific entry points for innovation include increasing awareness of parasitic weed problems among farmers, extension and crop protection officers and policymakers. In regions where awareness is relatively high, participatory research approaches can provide a basis for developing locally adapted parasitic weed management strategies. Generic entry points for innovation include enhanced collaboration and interaction between stakeholders across different levels, for example in multi-stakeholder platforms. This can provide the basis for developing and implementing coherent policy and development strategies to address structural constraints in the agricultural system, including the promotion of clean local seed systems, investments in physical and knowledge infrastructure development, adequate backstopping of agricultural extension officers, agribusiness training for farmers, quality control of agricultural inputs, timely access to agricultural inputs, and improved access to markets for farmers. Together the specific and generic entry points can strengthen the innovation capacity of Tanzania's agricultural system to address parasitic weed problems, as well as other complex agricultural problems

Farmers’ knowledge, use and preferences of parasitic weed management strategies in rain-fed rice production systems

Rain-fed rice production in sub-Saharan Africa is often hampered by parasitic weeds. This study assessed farmers’ awareness, use, preference and adoption criteria of parasitic weed management practices in rain-fed rice production environments in Tanzania. Surveys and workshops were organized in three affected rice growing areas in Morogoro-rural, Songea and Kyela district, supplemented with on-farm experiments in Kyela. In all districts, farmers were aware of the locally occurring parasitic weed species, Rhamphicarpa fistulosa (lowland) and Striga asiatica (upland), and they considered these weeds more problematic than non-parasitic weeds. Though they mostly practise hand weeding, farmers were aware of a wide range of control options. Local access, affordability, ease of implementation and control efficacy were considered important criteria for adoption, whereas trade-offs, like lack of preferred grain quality traits in resistant varieties, were mentioned as an important break on adoption. Based on informal discussions with farmers, altered sowing times, resistant rice varieties and soil amendments were marked as feasible control options and tested in a farmer-participatory manner in four years of experimentation in upland and lowland fields. In both types of fields, the contribution of soil amendment to parasitic weed suppression was not evident, but rice husk was marked as a suitable and cheap alternative to inorganic fertilizers. Control of R. fistulosa in lowlands was perceived to be best realized by early crop establishment, escaping major parasite damage due to the relatively slow early development of this weed species. The local variety Supa India, appreciated for its grain qualities and marketability, remained the preferred variety. For the control of S. asiatica, late planting was preferred, requiring a short-duration variety to minimize risk of drought stress during grain filling. The short-duration NERICA-10 was most preferred, as it combined a favourable short cycle length with resistance to S. asiatica and good grain appearance. Farmer participation in technology testing showed to be crucial in defining locally adapted and acceptable parasitic weed control strategies. Yet, it is argued that without lifting important constraints related to credit and input supply, it will be impossible to sustainably solve the parasitic weed problem in rain-fed rice

Evaluation of field resistance to Striga hermonthica (Del.) Benth. in Sorghum bicolor (L.) Moench. The relationship with strigolactones

BACKGROUND: Significant losses in sorghum biomass and grain yield occur in sub-Saharan Africa owing to infection by the root-parasitic weed Striga hermonthica (Del.) Benth. One strategy to avoid these losses is to adopt resistant crop varieties. For further delineation of the role of germination stimulants in resistance, we conducted a field experiment employing six sorghum genotypes, in eastern Sudan, and in parallel analysed the strigolactone levels in the root exudates of these genotypes under controlled conditions in Wageningen. RESULTS: The root exudates of these genotypes displayed large differences in strigolactone composition and Striga-germination-inducing activity. Korokollow, Fakimustahi and Wadfahel exuded the highest amounts of 5-deoxystrigol. Fakimustahi was by far the highest sorgomol producer, and Wadbaco and SRN39 produced the highest amount of orobanchol. The concentration of 5-deoxystrigol in the root exudate showed a significant positive correlation with in vitro Striga germination and was positively associated with Striga infection in the field experiments, whereas orobanchol was negatively associated with Striga infection in the field experiments. CONCLUSION: For the first time a close association is reported between strigolactone levels analysed under laboratory conditions and Striga infection in the field in sorghum genotypes. These genotypes may be used for further study of this resistance mechanism and for the introgression of the low germination trait in other sorghum varieties to breed for a strigolactone composition with low stimulant activity. The use of such improved varieties in combination with other Striga management tools could possibly alleviate the current Striga problem on the African continent

Heritability of growth and leaf loss compensation in a long-lived tropical understorey palm

Introduction Defoliation and light competition are ubiquitous stressors that can strongly limit plant performance. Tolerance to defoliation is often associated with compensatory growth, which could be positively or negatively related to plant growth. Genetic variation in growth, tolerance and compensation, in turn, plays an important role in the evolutionary adaptation of plants to changing disturbance regimes but this issue has been poorly investigated for long-lived woody species. We quantified genetic variation in plant growth and growth parameters, tolerance to defoliation and compensation for a population of the understorey palm Chamaedorea elegans. In addition, we evaluated genetic correlations between growth and tolerance/compensation. Methods We performed a greenhouse experiment with 711 seedlings from 43 families with twelve or more individuals of C. elegans. Seeds were collected in southeast Mexico within a 0.7 ha natural forest area. A two-third defoliation treatment (repeated every two months) was applied to half of the individuals to simulate leaf loss. Compensatory responses in specific leaf area, biomass allocation to leaves and growth per unit leaf area were quantified using iterative growth models. Results We found that growth rate was highly heritable and that plants compensated strongly for leaf loss. However, genetic variation in tolerance, compensation, and the individual compensatory responses was low. We found strong correlations between family mean growth rates in control and defoliation treatments. We did not find indications for growth-tolerance/compensation trade-offs: genetic correlation between tolerance/compensation and growth rate were not significant. Implications The high genetic variation in growth rate, but low genetic variation in tolerance and compensation observed here suggest high ability to adapt to changes in environment that require different growth rates, but a low potential for evolutionary adaptation to changes in damage or herbivory. The strong correlations between family mean growth rates in control and defoliation treatments suggest that performance differences among families are also maintained under stress of disturbance.ISSN:1932-620