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CONTEXT: Over the past two decades, the Mekong region has experienced significant transformation of its agricultural sector from subsistence farming to export crops driven by the expansion of agricultural land and of irrigation, plus intensification thanks to mechanization and the use of chemical inputs. In the context of agrarian transition, maintaining “organic by default” rice farming systems that do not rely on chemical inputs, is challenging. OBJECTIVE: Based on a case study in Preah Vihear, the organic province of Cambodia, this paper examines whether organic rice certification can maintain “organic by default” practices in a context of unprecedented agricultural intensification. METHODS: Using agrarian diagnosis, we investigated the impacts of an organic rice certification scheme on the future of organic rice-based farming systems. We built a functional typology of five farming systems that co-exist in the study area to understand the roles of organic rice in each system. RESULTS AND CONCLUSIONS: From an economic perspective, organic rice is less profitable than recently introduced cash crops, e.g. cassava, cashews. The positive impact of certification of organic rice is threatened by lock-in factors, e.g. labor diversification in both farming and non-farming activities, cash flow management, the certification process, leading farmers to abandon organic rice for cash crops for export. We discuss the key role of agricultural cooperatives in the certification process of organic rice. SIGNIFICANCE: The paper questions the capacity of a certification scheme to keep up with the process of intensification that undermines the profitability of the remaining “organic by default” rice systems. Beyond the significance of the results in the study area, one of the last strongholds of traditional rice systems in Cambodia, the paper illustrates the disappearance of “organic by default” rice systems in the whole country as well as in the Mekong region.

Genomic selection is a worthy breeding method to improve genetic gain in recurrent selection breeding schemes. The integration of multi-generation and multi-location information could significantly improve genomic prediction models in the context of shuttle breeding. The Cirad-CIAT upland rice breeding program applies recurrent genomic selection and seeks to optimize the scheme to increase genetic gain while reducing phenotyping efforts. We used a synthetic population (PCT27) of which S0 plants were all genotyped and advanced by selfing and bulk seed harvest to the S0:2, S0:3, and S0:4 generations. The PCT27 was then divided into two sets. The S0:2 and S0:3 progenies for PCT27A and the S0:4 progenies for PCT27B were phenotyped in two locations: Santa Rosa the target selection location, within the upland rice growing area, and Palmira, the surrogate location, far from the upland rice growing area but easier for experimentation. While the calibration used either one of the two sets phenotyped in one or two locations, the validation population was only the PCT27B phenotyped in Santa Rosa. Five scenarios of genomic prediction and 24 models were performed and compared. Training the prediction model with the PCT27B phenotyped in Santa Rosa resulted in predictive abilities ranging from 0.19 for grain zinc concentration to 0.30 for grain yield. Expanding the training set with the inclusion of the PCT27A resulted in greater predictive abilities for all traits but grain yield, with increases from 5% for plant height to 61% for grain zinc concentration. Models with the PCT27B phenotyped in two locations resulted in higher prediction accuracy when the models assumed no genotype-by-environment (G × E) interaction for flowering (0.38) and grain zinc concentration (0.27). For plant height, the model assuming a single G × E variance provided higher accuracy (0.28). The gain in predictive ability for grain yield was the greatest (0.25) when environment-specific variance deviation ef

Dans le contexte de l'agriculture tropicale, la faible adoption de nouvelles variétés proposée par la recherche agronomique interpelle la mise en oeuvre de programmes de sélection participative décentralisée (SPD). La fonctionnalité de ces derniers reste cependant peu documentée. Nous questionnons cette dernière en posant l'hypothèse qu'elle est reliable à la génération de différentes ressources dans l'activation des capacités à innover collectivement. Ce test est méthodologiquement renseigné par un dispositif d'enquête dans le cadre d'une SPD sur le riz pluvial dans les Hautes Terres de Madagascar. Les résultats révèlent des changements liés à la participation à cette SPD dans les systèmes de production (utilisation d'autres types de fertilisation, application des techniques de semis en carré pour faciliter le sarclage) et la réutilisation des nouvelles variétés testées. Ils confirment aussi le renforcement du lien social par la structuration d'une organisation paysanne. Ils caractérisent enfin les principales capacités à innover qui ont été renforcées, notamment celles qui conduisent à comprendre un système complexe et apprendre à agir collectivement.

Background. Asian rice Oryza sativa, first domesticated in East Asia, has considerable success in African fields. When and where this introduction occurred is unclear. Rice varieties of Asian origin may have evolved locally during and after migration to Africa, resulting in unique adaptations, particularly in relation to upland cultivation as frequently practiced in Africa. Methods. We investigated the genetic differentiation between Asian and African varieties using the 3000 Rice Genomes SNP dataset. African upland cultivars were first characterized using principal component analysis among 292 tropical Japonica accessions from Africa and Asia. The particularities of African accessions were then explored using two inference techniques, PCA-KDE for supervised classification and chromosome painting, and ELAI for individual allelic dosage monitoring. Key Results. Ambiguities of local differentiation between Japonica and other groups pointed at genomic segments that potentially resulted from genetic exchange. Those specific to West African upland accessions were concentrated on chromosome 6 and featured several cAus introgression signals, including a large one between 17.9 and 21.7 Mb. We found iHS statistics in support of positive selection in this region and we provide a list of candidate genes enriched in GO terms that have regulatory functions involved in stress responses that could have facilitated adaptation to harsh upland growing conditions.

Introduction: Rice plays a critical role in human livelihoods and food security. However, its cultivation requires inputs that are not accessible to all farming communities and can have negative effects on ecosystems. simultaneously, ecological research demonstrates that biodiversity management within fields contributes to ecosystem functioning. Methods: This study aims to evaluate the mixture effect of four functionally distinct rice varieties in terms of characteristics and agronomic performance and their spatial arrangement on the upland rice performance in the highlands of Madagascar. The study was conducted during the 2021-2022 rainfall season at two close sites in Madagascar. Both site differ from each other's in soil properties and soil fertility management. The experimental design at each site included three modalities: i) plot composition, i.e., pure stand or binary mixture; ii) the balance between the varieties within a mixture; iii) and for the balanced mixture (50% of each variety), the spatial arrangement, i.e., row or checkerboard patterns. Data were collected on yields (grain and biomass), and resistance to Striga asiatica infestation, Pyricularia oryzea and bacterial leaf blight (BLB) caused by Xanthomonas oryzae-pv from each plot. Results and discussion: Varietal mixtures produced significantly higher grain and biomass yields, and significantly lower incidence of Pyricularia oryzea compared to pure stands. No significant differences were observed for BLB and striga infestation. These effects were influenced by site fertility, the less fertilized site showed stronger mixture effects with greater gains in grain yield (60%) and biomass yield (42%). The most unbalanced repartition (75% and 25% of each variety) showed the greatest mixture effect for grain yield at both sites, with a strong impact of the varietal identity within the plot. The mixture was most effective when EARLY_MUTANT_IAC_165 constituted 75% of the density associated with other varietie

Description du sujet. Pour la zone écologique du Moyen-Ouest des plateaux d'altitude de Madagascar, six variétés de riz pluvial ont été sélectionnées par un programme de recherche. Objectifs. Il s'agit d'évaluer leur potentiel de diffusion en milieu réel. Méthode. Elles ont été co-évaluées sur un réseau de 20 fermes de référence pendant deux années. Résultats. L'expérimentation multi-locale a montré une gamme variée d'environnements indiquée par le rendement grain moyen en riz entre 1,04 à 4,50 t·ha-1, dans laquelle FOFIFA 182 s'est montrée significativement supérieure (2,90 t·ha-1) et SCRID 195 largement inférieure (1,65 t·ha-1), avec un groupe de quatre variétés non différenciées (autour de 2,40 t·ha-1). L'étude de l'interaction génétique-environnement a permis de différencier une variété produisant moins bien en milieu peu fertile, SCRID 90, et une moins stable, SCRID 91. SCRID 195, la variété la moins performante en termes de rendement, s'est montrée également la plus infectée par Striga asiatica, une plante hémiparasite. L'évaluation réalisée par les agriculteurs au terme de ces deux années complète celle de la recherche concernant le rendement du riz et le Striga, leurs principaux critères de performances des variétés, associés à six autres critères secondaires concernant le battage, la précocité, la résistance à la sècheresse, la qualité de grain, le gout et le poids de grain. Conclusions. Cette co-évaluation recherche-agriculteurs a permis de définir les variétés les plus performantes en termes de rendement et de contrôle du Striga, à savoir NERICA 4 (déjà vulgarisée) et FOFIFA 182 (proposée à la vulgarisation), de préciser l'intérêt de nouvelles variétés pour d'autres critères retenus par les agriculteurs et comme perspectives, la nécessité d'intégrer une approche systèmes de culture et une dimension temporelle, en lien avec la performance du riz pluvial.

In Madagascar, upland rice cropping is constrained by soil acidity and low phosphorus (P) bioavailability. Given their role in plant P nutrition, arbuscular mycorrhizal fungi (AMF) may improve crop yield in nutrient-poor tropical soils. In the Vakinankaratra region, a field experiment was conducted at 908 m asl on an acidic Ferralsol during the 2019–2020 growing season. The aim was to test the ability of four promoted rice varieties to respond to AMF seed-coating inoculation with a commercial strain of Rhizophagus irregularis in the absence or presence of P fertilizer (20 kg ha−1 of P2O5) under no expected nitrogen (N) limitation. In absence of P fertilization, both at tillering and at maturity and irrespective of the rice varieties, AMF inoculation significantly improved plant performance and finally grain yield, grain N, and grain P amounts by an average of 28%, 30%, and 39%, respectively. In contrast, when P fertilizer was supplied, no significant effect of AMF inoculation was observed. Rice growth variables were significantly higher with the application of P fertilizer than with AMF inoculation both at tillering and at maturity. P fertilizer without inoculation provided an average grain yield improvement of 85%. At tillering, mycorrhizal parameters for root colonization assessment were not positively linked with rice growth variables suggesting an early effect of AMF inoculation. We concluded that, with no P fertilization, AMF seed coating inoculation at the field scale significantly improved upland rice plant performance in a limited soil P environment. Our rice genetic variability did not interfere significantly both with mycorrhizal parameters and crop AMF inoculation benefits.

La croissance de la population des pays en développement impose parfois des besoins d'accroissement de la production agricole. Un projet de fertilisation phosphatée de la riziculture pluviale à Madagascar a été mené de façon participative entre des acteurs de recherche et des agriculteurs pour rehausser le rendement. Cependant, l'adoption de l'innovation a été très vite abandonnée par les agriculteurs. La démarche ImpresS (Impact des Recherches au Sud) a été utilisée sur ce projet pour évaluer ses impacts en élaborant un modèle répondant aux conditions d'adoption de l'innovation. Malgré l'abandon précoce de l'engrais cible (le phosphore minéral), la démarche ImpresS a permis d'identifier des processus qui ont amené aux impacts. Les résultats identifient un modèle d'innovation se présentant sous forme d'interaction ou de coproduction de connaissances entre les différents acteurs. Cette interaction permet de renforcer les capacités de tous les acteurs du projet à changer de pratiques ou à innover. En effet, les renforcements de capacités permettent à tous les acteurs engagés d'acquérir des impacts qui sont des nouvelles capacités techniques et fonctionnelles. Il en est déduit des réflexions collectives pour l'élaboration de futurs projets incluant une " culture d'impact " permettant une meilleure adoption de l'innovation apportée par la recherche.

Genome-wide association study (GWAS) was performed for 16 agronomic traits including nitrogen use efficiency (NUE) and yield-related components using a panel of 190 mainly japonica rice varieties and a set of 38 390 single nucleotide polymorphism (SNP) markers. This panel was evaluated under rainfed upland conditions in Madagascar in two consecutive cropping seasons with two contrasted nitrogen input levels. Using another set of five grain traits, we identified previously known genes (GW5, GS3, Awn1 and Glabrous1), thus validating the pertinence and accuracy of our datasets for GWAS. A total of 369 significant associations were detected between SNPs and agronomic traits, gathered into 46 distinct haplotype groups and 28 isolated markers. Few association signals were identified for the complex quantitative trait NUE, however, larger number of quantitative trait loci (QTLs) were detected for its component traits, with 10 and 2 association signals for nitrogen utilization efficiency and nitrogen uptake efficiency, respectively. Several detected association signals co-localized with genes involved in nitrogen transport or nitrogen remobilization within 100 kb. The present study thus confirmed the potential of GWAS to identify candidate genes and new loci associated with agronomic traits. However, because of the quantitative and complex nature of NUE-related traits, GWAS might have not captured a large number of QTLs with limited effects.

The evolution of varietal creation methods led in 2012 to the advent of the genome editing technique, CRISPR-CaS9. This technique would make it possible to create new varieties quickly and cheaply. Although some consider CRISPR-CaS9 to be revolutionary, others consider it a potential societal threat. To document the controversy, we explain the socioeconomic conditions under which this technique could be accepted for the creation of a rainfed rice variety in Madagascar. The methodological framework is based on 38 individual and semistructured interviews, a multistakeholder forum with organizations interviewedo, and a survey of 148 rice producers. Results reveal that the acceptability of genome editing requires (i) strengthening the seed system through the operationalization of regulatory structures and the upgrading of stakeholders' knowledge of genetically modified organisms, (ii) assessing the effects of the edited variety on biodiversity and soil nitrogen dynamics, and (iii) strengthening the technical and human capacities of the biosafety body. Structural mechanisms for regulating the seed system are necessary to ensure safe experimentation of genome editing techniques. Organizational innovation also appears to be necessary. The study documents how collective learning between communities of scientists and nonscientists is a component of systemic processes of varietal innovation.

Agroecology is based on the optimization of ecological processes occurring in agrosystems, especially by improving beneficial interactions among organisms. Recent studies have provided evidence that the ability of plants to interact with free-living soil organisms can be influenced by plant breeding. The upland rice breeding programme in the Highlands of Madagascar aims to develop cultivars that are adapted to local climatic, soil fertility and pest constraints. However, it is still unknown whether this genetic improvement alters rice cultivar abilities to interact with free-living soil plant-mutualistic organisms such as earthworms. We assessed in mesocosms the response of six upland rice cultivars commonly used by farmers in the Highlands of Madagascar to the presence of the endogeic earthworm Pontoscolex corethrurus. Plant nutrition and growth-related traits were measured after eight weeks of growth. These traits were significantly improved in the presence of P. corethrurus for all cultivars compared to the control treatment. However, the magnitudes of earthworm effects on plant traits were strongly variable and were dependent on specific rice cultivars. Agronomic and phylogenetic distance matrices were computed using agronomic data and available phylogenetic data of the rice cultivars. We did not detect significant correlations between cultivar responses to earthworm inoculation and agronomic or phylogenetic distances. Our results suggest that (i) the ability of rice to exploit beneficial interactions involving free-living soil organisms is influenced by its genetic background, but (ii) the loss of earthworm-interactive abilities of rice crops is independent of the genetic distance among cultivars and breeders' agronomic criteria. Our findings are significant for attempts to use rice cultivars that optimize plant-soil interactions within agroecological practices and highlight the need to integrate free-living soil partners as life-long plant partners in future s

Plant diversification is one of the main ways to ecologically intensify agroecosystems to improve their sustainability and resilience. Rotations and/or a mixture of crops can mitigate pest and weed infestation, reduce diseases, and improve soil fertility and crop productivity. However, rainfed rice yields in the Malagasy highlands remain low despite the frequent use of cropping systems including crop rotations and mixtures. In this study, we compared three rainfed rice based short rotations with rainfed rice monocropping to quantify the benefits of plant diversification on different ecosystem functions such as weed and nematode control, soil fertility, soil macrofauna abundance and diversity, and rice yield over four cropping seasons. The three rotations were based on rice in rotation with one legume, groundnut (RG), a cereal-legume mixture, sorghum and cowpea (RSC), or a mixture of legumes, velvet bean and crotalaria (RVC). Rice growth, N content and yield, soil N content, weed biomass, nematofauna and macrofauna were assessed and a profitability analysis was performed at rotation scale. The legume mixture had a significant and positive effect on rice growth, N content and yield, soil N content, and weed and nematode control due to high biomass production in the cropping cycle including legume mixture, by limiting weed growth and leaving a large quantity of N-rich residues to enrich the soil for the following rice crop. The nematicide properties of the legume mixture may reduce the infestation of plant-feeding nematodes. The RG and RSC rotations produced intermediate results. While rice yields were higher in these rotations than when rainfed rice was grown alone, weed biomass remained high due to minimal competition with weeds during the crop rotation cycle especially with groundnut. For RSC, nematode control was limited as both sorghum and cowpea are host plants for nematodes. Despite a year with no crop income with the RVC rotation, profitability was higher mainl

Cet article est basé sur des données empiriques qui permettent de caractériser, pour chaque exploitation agricole, les pratiques de gestion de la fertilité effectivement utilisées sur les parcelles cultivées au cours de l'année agricole 2016/17. A partir des budgets de culture, établis pour toutes les parcelles, la part des charges de fertilisation est mise en relation avec les marges brutes dégagées par culture.

In the context of subsistence farming in Madagascar, upland rice producers have limited access to mineral fertilizers and yields remain very low. Genetic improvement of yield through the nitrogen use efficiency (NUE) component is an avenue to be explored in breeding programs. A recent GWAS study carried out on an upland rice diversity panel allowed to detect genomic regions involved in NUE variability, nevertheless these regions explained only a moderate part of the total genetic diversity observed in the panel. We investigated the potential of genomic prediction for NUE in order to optimize our upland rice breeding program for this trait. We evaluated the predictive ability of genomic prediction using two validation experiments. The first consisted of a standard cross-validation with 5-fold subdivision of the diversity panel (DP) and the second consisted of an independent experiment involving a breeding population (BP) derived from the DP. The DP was structured into five genetic clusters of different sizes and with some degree of admixture, while the BP was composed of two main clusters. The best prediction ability for NUE was obtained in crossvalidation within the DP. The predictive ability in the independent validation experiment was weak (r = 0.25), about three times less than those obtained in the cross-validation. The low kinship between DP and BP, different genetic structures and slightly different LD patterns probably explains the low predictive ability of across populations genomic prediction. Practical implications for our rice breeding program are discussed.

Soil redox potential is an important factor affecting soil functioning. Yet, very few agronomy studies included soil redox potential in relation to soil processes. The objective of this study was to evaluate the spatial and temporal variation in soil redox potential and to determine the soil parameters affecting its variation. Soil redox potential, soil moisture, soil temperature, pH and bulk electrical conductivity were measured in upland rice fields during two growing seasons at six positions along an upland–lowland continuum, including two positions at the upland, two at the fringe and two at the lowlands in central Côte d'Ivoire (West Africa). The measurements were made at the following soil depths: 3, 8, 20 and 35 cm. Soil redox potential varied between 500 and 700 mV at the upland positions, 400 and 700 mV at the fringe positions and 100 and 750 mV at the lowland positions, and increased with soil depth. Variations in soil redox potential were driven by soil moisture, bulk electrical conductivity and soil organic carbon. We concluded that for proper interpretation of soil redox potential, sampling protocols should systematically include soil pH, moisture and bulk electrical conductivity measurements.

L'évaluation de la durabilité des systèmes de culture est un enjeu particulier dans des exploitations de subsistance proches du seuil de pauvreté, s'intensifiant et s'intégrant rapidement au marché. Le défi est double : prendre en compte à la fois les objectifs socio-économiques à court terme des agriculteurs (sortir de la pauvreté, sécurité alimentaire, revenus) tout en fournissant des indications sur la manière d'éviter que les transitions rapides conduisent à une agriculture conventionnellement intensifiée avec des dommages sociaux et environnementaux irréversibles. L'objectif de cette thèse est de contribuer aux travaux sur les méthodes d'évaluation intégrée et multicritère discutant de compromis localement les plus acceptables entre objectifs socio-économiques de court terme et objectifs de durabilité à long terme pour des systèmes de culture dans des fermes en transition. La thèse développe une approche originale qui combine de nombreux outils méthodologiques en 3 étapes: 1) Identification de critères de durabilité localement pertinents en associant les perspectives des agriculteurs aux résultats d'un diagnostic agronomique adapté, 2) Diagnostic agro-environnemental pour quantifier les indicateurs de durabilité de différents types de système de culture pratiqués par les agriculteurs et quantification des marges de progrès pour améliorer la durabilité suivant les zones biophysiques auxquelles les agriculteurs accèdent, 3) Evaluation de la variabilité des marges de manoeuvre pour augmenter la durabilité suivant le type de ferme et les objectifs des agriculteurs. Le cas d'étude est le Nord-Laos. Des systèmes de culture de subsistance à base de riz pluvial se sont transformés en 20 ans en monoculture mécanisée de maïs hybride avec des risques accrus sur l'environnement. Dans ces systèmes de production qui combinent une production autoconsommée et une agriculture orientée vers le marché, l'étape 1 de cette thèse montre que les agriculteurs ont des préoccupations so

La riziculture pluviale prend une place importante dans les exploitations agricoles Malagasy, en particulier sur les " tanety " des Hautes terres et du Moyen Ouest. Pourtant, les sols de " tanety " sont souvent très peu fertiles, notamment, en azote, qui est un facteur limitant du rendement des céréales comme le riz. De plus, les riziculteurs n'ont pas les moyens d'apporter des engrais chimiques et les rendements restent très faibles. L'enjeu de l'amélioration de l'efficience de l'utilisation de l'azote (NUE) est donc crucial dans ce contexte d'agriculture de subsistance ayant très peu recours aux engrais chimiques. La création de variétés pour ces systèmes à bas niveau d'intrants doit être envisagée. L'objectif global de cette étude est donc de contribuer à une meilleure compréhension du déterminisme génétique du NUE du riz pluvial et de l'élaboration du rendement en grains en fonction de la nutrition azotée. Pour ce faire, deux expérimentations ont été menées à Ivory, dans le Moyen Ouest de Madagascar, pendant quatre campagnes successives (2012 à 2016) pour évaluer le niveau de variabilité génétique existant pour NUE et d'autres caractères agronomiques, et pour identifier les régions chromosomiques responsables de la variation de ces caractères sur le riz pluvial, à l'aide de la génétique d'association (GWAS). La première expérimentation a été menée sur 13 variétés de riz pluvial dans un dispositif en bloc randomisé avec six répétitions et deux niveaux de fertilisation azotée (faible et fort), pendant trois campagnes (2012 à 2015). Au total, 21 caractères ont été mesurés dont le NUE et ses composantes ainsi que le rendement en grains (GY) et ses composantes. Une variabilité génétique pour NUE et ses deux composantes, ainsi que pour tous les autres caractères mesurés, a été montrée sur le riz pluvial. La variation de l'efficience de l'absorption de l'azote (NUPE) contribue le plus, fortement, à la variation de NUE, quel que soit le niveau d'azote du milieu. Nous n'

Since the early 2000s conservation agriculture (CA) has been promoted in the Lake Alaotra region of Madagascar for a more sustainable and profitable agriculture. There is, however, little known about its performance in low-input rainfed rice-based cropping systems. We conducted a study during two growing seasons (2013/14 and 2014/15) on an experiment that was established in 2009 at the agricultural research station of the National Center for Applied Research and Rural Development (FOFIFA) in the Lake Alaotra region of Madagascar. The experimental setup was a randomized block design with four replications. Two soil/residue management treatments were studied, conventional tillage without residue retention (CT) and no-tillage with residue retention (NT). These two treatments were tested for a 2-year rotation of maize + Dolichos lablab followed by rice (MD//R) and a 3-year rotation of maize + Stylosanthes guianensis, followed by S. guianensis in the second year, and rice in the third year (MS//S//R). During the 2013/14 and 2014/15 seasons, two levels of weed pressure: 'high' and 'low' were introduced as a split-plot design on the rice plots. The main determining factors of rice yield in the study region were studied: radiation interception, weed infestation, soil moisture and soil mineral nitrogen (N). Our results showed that five to six years of continuous practice of NT with retention of high amounts of crop residues (more than 5 Mg DM ha−1) on the soil surface had a significant (p = 0.02) positive effect on rice yield, irrespective of the level of weed pressure and type of crop rotation. CA systems significantly (p < 0.05) reduced weed density and biomass as compared to CT particularly during the vegetative stage of the rice crop in the two growing seasons, which to a certain extent explained the yield gains under CA. In contrast, treatment effects on soil moisture and mineral N contents were marginal. The positive effects of CA on reduced weed pressure may constitut

Rice is the most important food crop in the developing world. For rice production systems to address the challenges of increasing demand and climate change, potential and on‐farm yield increases must be increased. Breeding is one of the main strategies toward such aim. Here, we hypothesize that climatic and atmospheric changes for the upland rice growing period in central Brazil are likely to alter environment groupings and drought stress patterns by 2050, leading to changing breeding targets during the 21st century. As a result of changes in drought stress frequency and intensity, we found reductions in productivity in the range of 200–600 kg/ha (up to 20%) and reductions in yield stability throughout virtually the entire upland rice growing area (except for the southeast). In the face of these changes, our crop simulation analysis suggests that the current strategy of the breeding program, which aims at achieving wide adaptation, should be adjusted. Based on the results for current and future climates, a weighted selection strategy for the three environmental groups that characterize the region is suggested. For the highly favorable environment (HFE, 36%–41% growing area, depending on RCP), selection should be done under both stress‐free and terminal stress conditions; for the favorable environment (FE, 27%–40%), selection should aim at testing under reproductive and terminal stress, and for the least favorable environment (LFE, 23%–27%), selection should be conducted for response to reproductive stress only and for the joint occurrence of reproductive and terminal stress. Even though there are differences in timing, it is noteworthy that stress levels are similar across environments, with 40%–60% of crop water demand unsatisfied. Efficient crop improvement targeted toward adaptive traits for drought tolerance will enhance upland rice crop system resilience under climate change.

El arroz en Latinoamérica y el Caribe (LAC) es un cultivo de gran importancia social y económica. El consumo de arroz en LAC ha aumentado significativamente durante los últimos años, registrando un promedio actual de 30 kg persona-1 año-1. La particularidad del arroz producido en LAC está en una alta calidad de grano y una producción que se realiza en su mayoría bajo sistemas mecanizados con siembra directa. En LAC, el arroz es producido bajo riego y secano dentro de diferentes eco-regiones (templado, tropical húmedo, tropical seco). La seguridad alimentaria y el cambio climático constituyen un reto para la producción de arroz en LAC, elevando la necesidad de aumentar, pero a su vez estabilizar los rendimientos y la calidad del grano. La modelación de cultivos permite evaluar potenciales estrategias de adaptación. Estas herramientas permiten conocer, de forma anticipada, el comportamiento de las variedades de arroz bajo diferentes ambientes (combinaciones de suelo, clima, manejo y sus interacciones). Esto permite proyectar no solo los cambios en rendimiento y manejo del cultivo, pero también entender los procesos eco-fisiológicos que causan dichos cambios. El objetivo del presente trabajo es recopilar información relevante sobre el cultivo de arroz en LAC, para su uso para calibración y/o validación de los modelos de simulación de crecimiento de cultivos. La información recabada incluye (1) generalidades sobre estudios de modelación existentes en LAC; (2) datos de crecimiento y desarrollo de variedades en ensayos experimentales; y (3) datos generales (a nivel nacional) de manejo del cultivo en LAC. A través de una revisión de literatura se encontraron estudios de modelación publicados para cuatro países de Latinoamérica: Brasil, Venezuela, Chile y Cuba. Se colectaron y organizaron datos de un total de 65 ensayos eco-fisiológicos para calibración y evaluación de modelos mecanísticos para dos países: Brasil y Colombia. Estas bases de datos incluyen información básica

Enhancing rice yield in upland rice systems through genetic improvement remains a major challenge in the tropics. This review aims to provide the trends on upland rice cultivation over the last 30 years and recent distribution of upland rice in the tropics, and to report progress in studies on genetic improvement for enhancing productivity in Africa, Asia, and Latin America. While upland rice cultivation area has reduced in Asia and Latin America over the last 30 years, the area in Africa has increased. The current share of upland rice area in total rice area is related to rainfall and gross national income per capita, especially in Africa, and higher share is associated with lower rice self-sufficiency at national level. Breeding programs in Asia and Latin America have developed high-yielding varieties using indica materials as parents. In Africa, New Rice for Africa (NERICA) varieties were developed from crosses between improved tropical japonica and Oryza glaberrima. However, recent studies report that there is scope for improving existing NERICA using upland indica materials from Asia. In highlands of Africa, there are ongoing breeding programs using japonica varieties, such as the Nepalese Chhomrong Dhan. Key important plant traits used in the breeding programs are not largely different across regions, especially intermediate plant height and tillering capacity (which may be related to weed-suppressive ability), and high harvest index. In conclusion, we propose an international network for breeding upland rice with accelerating seed exchange across regions that could enhance upland rice productivity through genetic improvement.

La pauvreté du sol en éléments nutritifs disponibles pour les plantes est l'un des facteurs responsables d'une production agricole faible dans les Hautes Terres de Madagascar. La fertilité du sol et la production agricole peuvent être améliorées par le recyclage des biomasses végétale et animale. Nous avons testés deux options techniques basées sur ce recyclage des biomasses : l'agriculture de conservation (AC) et le fumier amélioré. L'objectif de l'étude est d'évaluer leurs impacts sur le rendement en grain des cultures. Des essais ont été conduits en milieu contrôlé et paysan, en comparant trois systèmes de culture : (i) riz//maïs+haricot (R//M+H) en labour, (ii) riz//maïs+Crotalaria grahamiana en AC et (iii) riz//avoine+vesce en AC ; et quatre types de fertilisation : (i) sans fertilisation,(ii) 5 t.ha‐1 de fumier conventionnel (13 gN.kg‐1 MS, (iii) 5 t.ha‐1 de fumier amélioré (26 gN.kg‐1 MS) et (iv) fumier conventionnel plus fumure minérale (100 kg.ha‐1 de NPK 11‐22‐16+100 kg.ha‐1 d'Urée à 46%N). Les résultats montrent que le fumier amélioré a permis d'augmenter le rendement en riz (jusqu'à 27 %) et le rendement total c'est‐à‐dire la somme des rendements en grain de chaque plante utilisé dans chaque système de culture (22 à 27%) par rapport au fumier conventionnel. Pendant l'année où la pluie a été mal répartie durant la campagne agricole, le rendement en riz de R//M+C en AC a été meilleur que celui de R//M+H en labour, avec une différence de 28%. Par contre, le rendement a été toujours plus faible avec le système R//A+V en AC, mais il pourra être compensé par l'effet sur la production laitière via l'utilisation du fourrage pour alimentation animale.

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.

Melioidosis, a severe infection with the environmental bacterium Burkholderia pseudomallei, is being recognised increasingly frequently. What determines its uneven distribution within endemic areas is poorly understood. We cultured soil from a rice field in Laos for B. pseudomallei at different depths on 4 occasions over a 13-month period. We also measured physical and chemical parameters in order to identify associated characteristics. Overall, 195 of 653 samples (29.7%) yielded B. pseudomallei. A higher prevalence of B. pseudomallei was found at soil depths greater than the 30 cm currently recommended for B. pseudomallei environmental sampling. B. pseudomallei was associated with a high soil water content and low total nitrogen, carbon and organic matter content. Our results suggested that a sampling grid of 25 five metre square quadrats (i.e. 25 × 25 m) should be sufficient to detect B. pseudomallei at a given location if samples are taken at a soil depth of at least 60 cm. However, culture of B. pseudomallei in environmental samples is difficult and liable to variation. Future studies should both rely on molecular approaches and address the micro-heterogeneity of soil when investigating physico-chemical associations with the presence of B. pseudomallei.

Objectif : Cette étude vise, à travers une analyse de la rentabilité financière, à mettre en exergue l'intérêt que peut susciter la production de semences de qualité dans les divers systèmes de production et la place du secteur privé dans la gestion du système semencier. Méthodologie et résultats : L'étude a été conduite auprès d'un échantillon de 57 producteurs de semences certifiées et de riz de consommation choisis de façon aléatoire dans trois départements : Mono, Zou et Collines où trois systèmes de production se côtoient. Il a été fait recours à la méthode d'analyse de marges et les résultats ont été comparés chaque fois à la production de riz de consommation par système de production : riz pluvial, riz de bas-fonds et riz irrigué. Il en résulte que la production de semences est plus rentable et l'est davantage dans le système d'irrigation. Conclusion et application des résultats : La présente étude a été conduite dans un contexte où l'État est intervenu pour promouvoir l'accès aux semences améliorées suite à la crise alimentaire de 2008. L'État, à travers son dispositif de vulgarisation organise, la collecte de semences auprès des producteurs multiplicateurs accrédités et subventionne la redistribution aux producteurs de riz de consommation. L'intérêt que porte cette étude sur la rentabilité financière de l'activité de production de semences certifiées réside dans la nécessité de disposer de données fiables pour susciter l'implication des entreprises privées dans le système semencier et faciliter l'accès aux crédits pour les multiplicateurs de semences. Pour un système compétitif et adéquat aux besoins des producteurs, il est impérieux de réfléchir sur un partenariat compagnies privées de distribution et producteurs multiplicateurs de semences certifiées. Ce dispositif facilitera la disponibilité et l'accès à un prix abordable aux semences de qualité pour les producteurs du riz.