We reviewed the potential of silicon (Si)-rich biochars (sichars) as crop amendments for pest and pathogen control. The main pathosystems that emerged from our systematic literature search were bacterial wilt on solanaceous crops (mainly tomato, pepper, tobacco and eggplant), piercing-sucking hemipteran pests and soil-borne fungi on gramineous crops (mainly rice and wheat), and parasitic nematodes on other crops. The major pest and pathogen mitigation pathways identified were: i) Si-based physical barriers; ii) Induction of plant defenses; iii) Enhancement of plant-beneficial/pathogen-antagonistic soil microflora in the case of root nematodes; iv) Alteration of soil physical-chemical properties resulting in Eh-pH conditions unfavorable to root nematodes; v) Alteration of soil physical-chemical properties resulting in Eh-pH, bulk density and/or water holding capacity favorable to plant growth and resulting tolerance to necrotrophic pathogens; vi) Increased Si uptake resulting in reduced plant quality, owing to reduced nitrogen intake towards some hemi-biotrophic pests or pathogens. Our review highlighted synergies between pathways and tradeoffs between others, depending, inter alia, on: i) crop type (notably whether Si-accumulating or not); ii) pest/pathogen type (e.g. below-ground/root-damaging vs above-ground/aerial part-damaging; "biotrophic" vs "necrotrophic" sensu lato, and corresponding systemic resistance pathways; thriving Eh-pH spectrum; etc.); iii) soil type. Our review also stressed the need for further research on: i) the contribution of Si and other physical-chemical characteristics of biochars (including potential antagonistic effects); ii) the pyrolysis process to a) optimize Si availability in the soil and its uptake by the crop and b) to minimize formation of harmful compounds e.g. cristobalite; iii) on the optimal form of biochar, e.g. Si-nano particles on the surface of the biochar, micron-sized biochar-based compound fertilizer vs larger biochar porous matrices.

Context: Intensive use of pesticides in rice paddies is harmful to both human health and biodiversity. As rice farmers tend to overuse pesticides, especially in the tropics, the use of decision support tools is one way for pesticide reduction. Various models have been developed to simulate the development of rice pests, or the impact of pests on the rice crop.Objective or research question: The objective of the review is to identify modeling approaches that may be useful for agroecological protection of rice crops against a wide range of pests, but not to provide an exhaustive review of models. We analyzed the scientific literature on rice pest, crop models integrating pest levels, and rice crop -pest models according to the number and type of pests simulated, the structure of the model, whether cropping practices are included in the simulation, the consideration of pest damages and yield losses, and hence the actual use of these models to improve crop protection strategy.Methods: We analyzed a total of 78 articles and 56 original models based on their structure, inclusion of pests, and cropping practices. Results: We identified 35 articles using pest models to simulate pest injuries; 34 articles using crop models to simulate the pest damages on yield losses; and 9 articles using crop-pest models to simulate the interactions between pest dynamics and crop growth.Conclusions: Different types of models offer different uses for ACP strategies. An innovative conceptual model for agroecological rice protection is proposed. Implications or significance: The presented review is a springboard to future modeling developments useful for agroecological rice protection. Combined with other approaches, such as field experiments and demonstrations, farmer workshops, teaching and training, specific advices to farmers, modeling approaches can help design more sustainable rice-based cropping systems.

Crop losses from pests threaten global food security and safety. In the last six decades, pest control using chemical pesticides has resulted in important yield gains per unit area, worldwide. However, the long-term sustainability of chemical pest control has been increasingly thrown into doubt due to the negative impact on human health, biodiversity, and the environment. Consequently, there is an urgent need to improve the science of crop protection in order to tackle the five key challenges of 21st century agriculture holistically: (i) maintaining or improving agricultural productivity, (ii) producing healthy food, (iii) reducing the negative impacts of agriculture on ecosystem and human health, (iv) ensuring the economic viability of farms, and (v) adapting agriculture to climate change. Agroecological Crop Protection (ACP) can be a powerful approach to address these challenges, as we demonstrate in this paper. ACP is the application of the principles of agroecology to crop protection in order to promote virtuous and sustainable changes in agriculture and food systems. ACP combines multiple approaches and disciplines including ecology, agroecology, and Integrated Pest Management. It promotes a crop protection system compatible with healthy agricultural and food systems, agroecological principles and the “one health” approach. We predict that ACP will meet the challenge of pesticide-free agriculture in the future. In this paper, we will first present the scientific, agricultural and social components of ACP. We will then analyze the research approaches, questions, methods and tools needed to adopt ACP. Finally, we suggest key mechanisms to facilitate the transition to ACP, which will ultimately provide sustainable food, feed, and fuel in a context of major global change.

We review interactions between crop protection practices (developed to control plant pathogens and invertebrate pests) and human fungal infectious diseases. Unlike viral, bacterial and parasitic infections, fungal infections in humans are usually only superficial in healthy individuals, but can become invasive and pose serious risks to immunosuppressed individuals. Although their global impact is less than that of other infectious diseases, human fungal infections still pose serious public health issues. For instance, the use of synthetic agricultural fungicides, particularly the azole class, under conventional intensive, or efficiency improvement-based crop protection practices, is at risk as far as antimicrobial resistance is concerned, due to cases of cross-resistance to clinical azoles used to treat pulmonary aspergillosis, candidiasis and cryptococcocis. In this respect, the One Health approach, originally designed for other types of human pathogens, looks relevant for human pathogenic fungi. Additionally, some entomopathogenic fungi used as biocontrol products against crop pests in a substitution-based approach, may be potentially pathogenic to humans. Very few examples of redesign-based practices ( i.e. Agroecological Crop Protection) emerged from our analysis on human fungal diseases. However, discontinuing agricultural azole fungicides (as practiced on organic farms, and which may to some extent be related to the redesign strategy) appears to be the best way to reduce selection pressure and hence the level of azole-resistant human pathogenic fungal strains in the environment.

Recent viral zoonotic epidemics have been attributed partially to the negative impact of human activities on ecosystem biodiversity. These encompass agriculture and specifically conventional agrochemistry-based crop protection (CP) practices. Here we review interactions between CP practices (whether against arthropod or vertebrate pests, plant pathogens, or weeds) and human infectious diseases (whether of bacterial, viral, parasitic, or fungal origin) with a focus on zoonotic diseases, in tropical agroecosystems. Antimicrobial resistance, which is an issue in public health, seems barely affected by conventional CP practices as far as viruses, bacteria, and parasitic protozoa and worms are concerned, but it is a major issue regarding human infections by fungal pathogens. Overall, Agroecological Crop Protection (ACP), by addressing major global challenges including climate resilience, biodiversity conservation, and animal welfare, is the preferred CP strategy for integrating crop plant health within the extended "One Health" concept.

Background The behavior of rice varieties under natural environments in fields often differs from the expected one. For developing varieties, breeders give then a particular importance to multi-local field screening to confirm the resistance of their germplasm. We assembled 81 accessions e.g. blast differential, traditional and improved varieties and tested them for resistance to blast ( Pyricularia grisea ) in eight African hot spots under different ecologies. We thus expected to identify accessions and genes or gene pyramids that provide durable resistance locally or across sites. Methods 81 accessions (e.g. blast differential, traditional and improved varieties were tested in hot spots in Benin, Burkina Faso, Côte d'Ivoire, Madagascar, Mali, Rwanda, Togo and Uganda for resistance to leaf and neck blast. An Alpha design (randomized incomplete block) with four replications was used. Correlation between leaf blast and neck blast severity and between incidence and severity were analyzed. Results: From 2013 to 2016, multi-local screening tests were conducted at yje selected sites. Among the 81 rice accessions tested, seven accessions were consistently susceptible while 12 were resistant across locations and seasons. Interestingly, effective individual resistance genes (R genes) or gene pyramids efficient across the sites were identified. In addition, we noticed on some sites, changes in the responses of some rice accessions to the disease from one season to the other. Responses of some accessions also showed great variations from one site to another. In addition, several accessions sharing the same resistance genes exhibited different responses to blast. Regarding the neck blast, only fewer accessions could be assessed as very susceptible ones died at early stages. Although differential responses were observed in the four sites considered for the analysis, several accessions consistently resisted. In addition, results showed that leaf and neck blast resistances were correlated. Conclusions Results obtained provide useful information on the tested germplasm resistance. In addition, it was possible to identify resistant accessions and sometimes the R genes associated which were effective locally or across sites. Results also showed shifts in pathogenicity of the pathogen populations over seasons and sites. Finally, breeders can now use this valuable information for sustainable blast resistance breeding.

Cereal-legume intercropping has gained increased interest in Europe. Nevertheless, performance and especially the percentage of each species at harvest are often considered highly variable. Nitrogen (N) fertilisation can be a relevant driving factor affecting the percentage of each species at harvest. Soil N availability influences competition for light and nitrogen in cereal-legume intercrops. However, management of N fertilisation still remains unclear for intercrops. Few references on the effects of a range of strategies of N fertilisation are available to guide farmers with relevant decision rules considering their expectations. Here, a modelling approach was proposed to simulate interactions between light and N acquisition of a pea-wheat intercrop and to test different scenarios for the management of such intercrops. A model (Azodyn-IC) was built resulting from the combination of two existing individual-crop models (AZODYN and AFISOL) and by applying rules of light and soil inorganic nitrogen sharing between the intercropped pea and wheat. Evaluation of the model outputs with experimental data showed satisfactory predictions of the studied variables (N accumulation, LAI, and crop dry weight). The model validated both resource sharing and light-N interactions. Furthermore, the model was able to respond to increases in inorganic N availability based upon straightforward formalisms. Simulating unmeasured variables, such as root growth and light interception and use by each species, improved our understanding of the relative dominance of each species for acquiring resources. Eventually, the model was used to simulate different scenarios of N fertilisation over 26 years of climatic data to account for climatic variability. We demonstrated the interest of such a modelling approach to design decision rules of N fertilisation according to farmers' expectations.

Revealing belowground-aboveground relationships (BAR) is essential to drive ecological processes to address agriculture dysfunctions, especially in the management of aboveground plant diseases. Earthworms are one of the most important soil organisms involved in BAR, and silicon (Si) has been identified as a crucial element regulating aboveground plant health. How earthworm-Si interactions induce BAR in poor- and rich-nutrient soil contexts is still poorly understood, despite a growing interest in agricultural sustainability. We investigated the potential of BAR induced by the earthworm-silicon interaction to control the severity of rice blast disease in a Ferralsol in Madagascar, with or without NPK fertilization. We conducted a greenhouse microcosm experiment in which we manipulated the presence of the endogeic earthworm Pontoscolex corethrurus and the fungus Pyricularia oryzae in a Ferralsol supplied or not with Si and fertilized with macronutrients (nitrogen, phosphorus and potassium, i.e., NPK). After eight weeks of growth, plant biomass, nutrition and disease severity were measured. Our results validated the hypothesis that a dual treatment of earthworm inoculation and Si fertilization in a nutrient-poor tropical soil confers a higher tolerance of rainfed rice to P. oryzae, in comparison with treatments with only earthworms or Si, providing the optimal agronomic balance between a gain in biomass (and nutrition) and a reduction in disease severity. The supply of macronutrients altered this positive BAR by favouring the phenomenon of N-induced susceptibility. The aboveground plant C:N ratio of 15 is a threshold below which any increase in N per C unit likely enhances blast disease. The role of belowground interactions to counteract agricultural dysfunctions is supported by our study. To accomplish ecological intensification and provision of ecosystem services such as disease regulation, our findings recommend replacing excessive use of macronutrient fertilizer with sustained agricultural practices promoting the development of earthworm populations, such as organic matter inputs, superficial or no tillage, and the use of cover crops or conservation agriculture.

In the densely populated highlands of Madagascar, growing upland rice offers the opportunity to increase the total rice cropping area and to improve food security. However, rice blast was a major constraint for the first cultivars released in the 1990s and consequently limited the extension of upland rice. However, blast epidemics are much less intense in the region of Betafo, where the composition of the soil, an Andosol developed from volcanic rock, is different from the classical Ferralsol of the highlands. A 3-year field experiment (2009–2011) was conducted near Antsirabe to compare blast epidemics on rice grown in Ferralsol vs. an Andosol. Leaf and panicle blast development were monitored and the yield components of upland rice plants growing on the two different soil orders were measured. In 2009 and 2011, leaf and panicle blast development were significantly lower for plants grown on the Andosol compared to those grown on the Ferralsol (final panicle blast reduced by 40% in 2009 and 20% in 2011). The severity of blast was shown to be related to the concentrations of mineral elements in the plant, and the Si content was significantly higher in plants growing on the Andosol. In 2010, the differences of blast incidence between the two soils were less marked (14% reduction of panicle blast at the last scoring date). AUDPC were lower in the Andosol compared to the Ferralsol each year, for leaf and panicle blast. The yield components 1000 full grain weight, dry straw weight and the yield were higher in the Andosol compared to the Ferralsol in 2009 and 2010 but were not significantly different in 2011. These results clearly document that blast development may be impacted by the soil order in which rice is grown, and future agronomic management of blast should focus on improved soil mineral composition such as silicon.

Magnaporthe oryzae is the fungal plant pathogen that causes rice blast. The sources of primary inoculum and overwintering mode of the fungus remain largely unknown. The effect of rice residues on the onset of blast epidemics and the potential for survival of M. oryzae in the residues were studied in upland conditions in Madagascar. Blast disease was observed in a 3‐year field experiment in three treatments: with either infected or uninfected rice residues on the soil surface, or without rice residues. Leaf blast incidence was significantly higher in the treatment with infected rice residues than in the two other treatments at the early stages of the epidemic. In a second set of trials, the survival of M. oryzae on rice residues was monitored. Infected rice stems were placed by lots in three places: on the mulch of rice residues, under the mulch, and buried at a depth of 10 cm in the soil. Each month, samples were taken from the field and tested for sporulation. The survival of the blast fungus decreased rapidly on the stems buried in the soil but remained high for the other conditions. Sporulation of the fungus was observed on stems left on the mulch for up to 18 months. It is concluded that under field conditions, the presence of infected rice residues could initiate an epidemic of blast. The results of this study may help in designing effective management strategies for rice residues infected by M. oryzae.

We tested the ability of root-adhering soils (RAS) from eight rice cultivars to attract a bacterivorous nematode (Acrobeloides sp.) living in a poor-nutrient soil in Madagascar. We showed that the ability of rice to attract bacterivorous nematodes in its rhizosphere is variable among cultivars. FOFIFA 172 was the cultivar with the highest attraction value, the lowest root biomass (RB) and the highest RAS: RB ratio and RAS respiration. In contrast, nematodes exhibited strong repellent response to W880 RAS. Also, nematode attractancy was not related to rice resistance against pests (blast rice disease and Striga asiatica) neither to cultivar ability to grow at specific altitude. Our results suggest a trade-off in carbon allocation between plant biomass and root exudation driving nematode attractancy and raise questions about the impact of plant breeding on cultivar ability to interact with soil mutualists such as bacterivorous nematodes. Further investigations are required into (i) variation in root exudate quantity and composition among the eight cultivars and (ii) the response of rice cultivars to bacterivorous nematode inoculation.

In the central highlands of Madagascar, blast, a serious fungal disease of rice caused by Magnaporthe oryzae, was shown to be less severe in conservation agriculture (CA) than in conventional tillage (CT) cropping systems. To assess the effects of CA cropping systems on rice susceptibility to blast and to understand the mechanisms involved, an experiment was conducted over three growing seasons in two sites (at high and mid-altitude). Two fertilization treatments, one with mineral nitrogen (N) fertilizer, and one without, were studied in interaction with two different cropping systems (CA/CT) and two rice varieties that differ in their susceptibility to blast. The performances of the two cropping systems were assessed, and results showed that yields were no higher in the CA or were lower than in CT cropping systems. The effects of the treatments on upland rice crop growth were measured by leaf N content as an indicator of N crop status, and leaf area index (LAI) as an indicator of canopy density. In all years at both sites, leaf N content during early growth stages was higher in the CT than in the CA cropping system. The LAI was lower in the CA than in the CT cropping system at the high altitude site in all three years, and in two out of three seasons at the middle altitude site. Overall, when the level of blast was high, blast was less severe in the CA cropping system and with no N fertilizer. Leaf N content and LAI were used as intermediate explanatory variables in the statistical analyses, and one or the other or both always masked the effect of the cropping system or of N fertilization. Our results show that leaf N content during early growth stages masks the effect of the cropping system on leaf blast severity. When the LAI is strongly affected by the cropping system, it also masks the effect of the cropping system on the severity of leaf and panicle blast. Very often both variables masked the effects of the cropping system and of N fertilization. These findings should help improve disease management by modifying fertilization practices and crop nutrition in conservation agriculture cropping systems. (C) 2017 Elsevier B.V. All rights reserved.

Rice yellow mottle virus (RYMV) is one of the main constraints for rice cultivation intensification in Africa leading to high yield losses [1]. Six major strains, with a well defined geographical distribution, have been identified and were characterized by a large range of pathogenic properties (infection abilities and symptom intensities) on the rice and few wild grasses [2]. Originated from Tanzania, the genetic diversity is maximal in this area where three out of six of the major strains are circulating [3]. It has been demonstrated that some agricultural practices, as seedbed to field transplantation and elimination of the wild rice and grasses, can influence the RYMV prevalence in fields [2]. However, no study has analyzed at the field scale the consequences of these agro-ecological modifications on the diversity and the dynamics of the viral populations. Thus, the main objective of this work is to measure the effects of the rice cultivation intensification (changes of the cultural practices, from traditional to intensive cultivation) and the environmental variability (cultivated and wild host diversity) on the RYMV populations in order to better understand the emergence, the propagation and the maintenance of the viral strains at the field scale. For that, the RYMV prevalence was first investigated in Tanzania in an “intensive” rice plantation and some surrounding “traditional” farms, taking in account the cultivation mode, the irrigation level, the rice phenological stage, the density and the diversity of the hosts (wild and cultivated). A distribution map of the RYMV in this area was build and we observed that the irrigation enhances the RYMV prevalence. Then, the analysis of the genetic diversity identified isolates belonging to the three major strains of East Africa in the same plantation. Finally, while no genetic structure of the virus diversity has been highlight between cultural practices, the analysis of the samples by depth sequencing is on progress in order to characterize and to compare precisely the intra-host genetic diversity and structure depending to the cultivation mode and to the host (wild or cultivated). Altogether, this study will allow us to understand the diversification processes and the flow of the viral populations at the field scale in order to participate to the improvement of the control strategies against the RYMV. (Resume d'auteur)

Evaluating cropping systems depends on the perspective and scale considered. An agronomic point of view is often considered with the assessment of the impacts of the cropping system at the field scale, or an economic point of view with the consequences of implementing a cropping system on the farm. Tools have been developed to enable a more integrative assessment of cropping systems. This is the case of the MASC (R) model which, using multicriteria evaluation, estimates the sustainability of cropping systems from environmental, economic and social perspectives. MASC-Mada was developed specifically for upland cropping systems in Madagascar. It has been used to compare conservation agriculture cropping systems with conventional cropping systems. The results, confronted to the opinion of farmers, show that conservation agriculture systems are generally more sustainable than conventional systems but a mixed system combining the use of cover crops and less frequent tillage would better take social and economic aspects into account.