Natural Flora Is Indiscriminately Hosting High Loads of Generalist Fungal Pathogen Colletotrichum gloeosporioides Complex over Forest Niches, Vegetation Strata and Elevation Gradient.

Crop pathogenic fungi may originate from reservoir pools including wild vegetation surrounding fields, and it is thus important to characterize any potential source of pathogens. We therefore investigated natural vegetation's potential for hosting a widespread pathogenic group, Colletotrichum gloeosporioides species complex. We stratified sampling in different forest environments and natural vegetation strata to determine whether the fungi were found preferentially in specific niches and areas. We found that the fungi complex was fairly broadly distributed in the wild flora, with high prevalence in every study environment and stratum. Some significant variation in prevalence nevertheless occurred and was possibly associated with fungal growth conditions (more humid areas had greater prevalence levels while drier places had slightly lower presence). Results also highlighted potential differences in disease effects of strains between strata components of study flora, suggesting that while natural vegetation is a highly probable source of inoculums for local crops nearby, differences in aggressiveness between vegetation strata might also lead to differential impact on cultivated crops.

Dynamics of Pathogenic Fungi in Field Hedges: Vegetation Cover Is Differentially Impacted by Weather.

Landscape effects might impede or increase spore dispersal and disease risk for crops, as trees and hedges buffer winds and can behave as spore traps, therefore limiting diffusion of fungi, or, on the contrary, behave as disease relay once vegetation is infected and become inoculum sources. In this study, we investigated weekly prevalence of the pathogenic fungus Colletotrichum gloeosporioides on guava tree leaves, differentiating impacts of leaf height on tree, age, and location within leaf. We first estimated differences in prevalence for each covariate, and then related infection rates to weather effects during the year. Our results highlighted a great variance of prevalence among individual trees, and a lower contamination of tree tops, as well as a tendency for greater odds of infection in tips of young leaves compared to older ones. Last, we show evidence that individual tree contaminations are associated with different disease dynamics: early and dispersal-based, late and growth-based, as well as with intermediate dynamic ranges. Pathogen infection dynamics will thus be greatly impacted by cover characteristics at local scale, and tree cover should not be perceived as homogeneously driving disease levels.

Weeds as Pathogen Hosts and Disease Risk for Crops in the Wake of a Reduced Use of Herbicides: Evidence from Yam (Dioscorea alata) Fields and Colletotrichum Pathogens in the Tropics.

The transition toward sustainable agriculture requires rethinking cropping systems in the light of less intensive and chemically reliant practices. Weed management is one of the target practices to evolve cropping systems with decreased impact on the environment. While softened management will lead to increased weeds/crops coexistence, it is of importance to assess the relative benefits and drawbacks of new practices. Among the potential drawbacks of weeds/crops coexistence, disease risk may increase if weeds are hosting pathogens. In this study, we assessed the potential of weeds for hosting pathogenic generalist fungi known to translate into disease in crops. We first describe prevalence in fields after harvest and relate prevalence to species characteristics and communities. Then, we directly test the idea that weeds serve as inoculums sources during cropping with a natural experiment. This study highlights variation in host skill among feral weeds for Colletotrichum species, including potential congeneric sub-specialization on different weeds within communities. Last, prevalence within fields was more correlated to focal crop inoculation rates compared to local weed load, but there was a significant correlation effect with prevalence on weeds in the vicinity of fields, suggesting that weeds are mediating disease levels at the local scale, too. Results pointed to the importance of weed host skill in disease risk yet open the door to the potential control of pathogens via targeted weed management.

Control of Amazonian Leaf-Cutting Ants (Hymenoptera: Formicidae): A Multi-criteria Analysis.

Leaf-cutting ants (Hymenoptera: Formicidae) are one of the main pests found in the Americas and they cause global economic losses worth several billions of dollars. While pesticides have been the most widely used control method, new management alternatives in a context of agroecological transition are now being considered. This study focuses on the leaf-cutting ants species found in the pan-Amazon region. As part of efforts to improve management of these pests, this multi-criteria analysis of control strategies covers a total of 691 experiments collected from 153 studies, and the control were evaluated as a function of their management efficacy, environmental and human health impacts, and their ease of application. Chemical control methods were effective but posed a danger to human health and the environment, whereas mechanical methods and integrated management were more sustainable but not always very effective. Some of the biocontrol methods were evaluated as effective and safe for the environment and human health, including the use of entomopathogenic fungi Beauveria bassiana (Bals.-Criv) Vuill. (Hypocreales: Cordycipitaceae) and Metarhizium anisopliae (Metschn.) Sorokïn (Hypocreales: Clavicipitaceae) in the form of bait or sprayed in the nest, or the application of plant mulch in the nest using Tithonia diversifolia (Hemsley) A. Gray (Asterales: Asteraceae) or Canavalia ensiformis L. DC. (Fabales: Fabaceae). Because of variations in the efficacy data between laboratory and field tests, we are in favor of evaluating these control methods during field studies with different leaf-cutting ant species and under different environmental conditions. These methods should adopt experimental arrangements that are appropriate for local socioeconomic conditions adapted for farmers.

Consumers' preferences for fresh yam: a focus group study.

In West and Central Africa and in the Caribbean, yam is one of the most important sources of carbohydrates and has a great potential to improve food security. The yam production sector is, however, now challenged by the satisfaction of evolving consumers' preferences. Since little is known about consumers' preferences regarding yams' characteristics, product quality, and the drivers of yam purchase, six focus group discussions were conducted (for a total of 31 participants). Among the purchasing criteria, price was considered more important than the others. It was followed by the external damage, the origin, and the size of the tuber. The most frequently cited consumption criteria were the taste, the texture, and color of flesh after cooking. Taste was considered more important than the other criteria. Three consumers' profiles were established reflecting heterogeneity in preferences, especially as concerns the willingness to pay for yam and consumption habits. They were designated as the Hedonistic, the Thrifty and the Flexible. Our results suggest that innovations can be implemented to sustain and stimulate the development of the yam sector in Guadeloupe. Two main development paths were identified. The first path is the valorization of the great existing diversity of yam varieties and the increase in the level of information for consumers about product attributes such as the cooking mode, the origin, and the mode of production. Building a marketing strategy based on the valorization of this diversity can help maintain and preserve yam's agro-biodiversity and the satisfaction of rapidly evolving consumption habits. The second path is the definition of yam ideotypes that suit consumers' needs. We expect that tailoring the production to consumers' needs will have a positive impact on global food security in the Caribbean region.

Acromyrmex octospinosus (Hymenoptera: Formicidae) management: effects of TRAMILs fungicidal plant extracts.

Leaf-cutting ants, Acromyrmex octospinosus (Reich), are considering among the most important pest species of the New World. Until now, the main insecticides used for controlling these ants were synthetic chemicals. Leaf-cutting ants live in obligate symbiosis with abasidiomycete fungus, Leucocoprinus gongylophorus (Heim) Moeller. The crucial role of this symbiotic partner in the nest of leaf-cutting ants has prompted us to focus on A. octospinosus management through the use of fungicides in our study. Five parts of plants identified for their antifungal potential through TRAMIL ethnopharmacological surveys were tested: 1) bulbs of Allium cepa L.; 2) seed pods of Allium sativum L.; 3) green fruits of Lycopersicon esculentum L.; 4) leaves of Manihot esculenta Crantz; and 5) leaves of Senna alata (L.) Roxburgh. One plant extract with strong fungicidal activity (S. alata) against L. gongylophorus was found. The other extracts had lesser fungistatic or fungicidal effects depending on the concentrations used. The data presented in this study showed that TRAMILs fungicidal plant extracts have potential to control the symbiotic fungus of leaf cutting ants, in particular a foliage extract of S. alata.

Acromyrmex octospinosus (Hymenoptera: Formicidae) management. Part 1: Effects of TRAMIL's insecticidal plant extracts.

BACKGROUND: Leaf-cutting ants are considered to be one of the most important pest species of the New World. Until now, control strategies against these leaf-cutting ants have mainly been synthetic chemicals. The aim of the present study was to test the action of several plant extracts quoted as an example by TRAMIL participative surveys for their insecticidal properties on adult major workers of Acromyrmex octospinosus. Three tests were used to that end: contact toxicity, repellent test and ingestion bioassay. Six traditional plant uses recommended by interviewed people in surveys were tested: (1) maceration of Mammea americana fresh crushed seeds; (2) decoction of Nerium oleander fresh leaves; (3) Nerium oleander dried leaf water juice; (4) decoction of Nicotiana tabacum dried leaves; (5) Trichillia pallida dried leaf water juice; (6) decoction of Rollinia mucosa dried seeds. RESULTS: Two plant extracts with contact toxicity (Mammea americana and Nicotiana tabacum), six plant extracts with repellent activity and four plant extracts with ingestion toxicity (Mammea americana, Nicotiana tabacum and both extracts of Nerium oleander) were found. CONCLUSION: The data presented in this study showed that plant extracts cited by TRAMIL ethnopharmacological surveys have the potential to control the leaf-cutting ant, Acromyrmex octospinosus. In particular, the Mammea americana extract, with its natural low repellent effect and its high toxicity by ingestion, and Nerium oleander extracts, with their natural delay action, are possibly the best extracts for the control of these ants.

TRAMIL ethnopharmalogical survey in Les Saintes (Guadeloupe, French West Indies): a comparative study.

AIM OF THE STUDY: The aim of this study was a comparison of popular household remedies in primary health care in the communities of Terre-de-Haut and Terre-de-Bas, the inhabited islands of 'Les Saintes' archipelago (Guadeloupe, French West Indies). METHODS: Twelve ailments, with higher prevalence, were chosen in each island and a total of 216 families were interviewed using TRAMIL participative ethnopharmacological interviews. RESULTS: According to TRAMIL methodology (frequency over 20%), twenty-two plants uses were recorded for Terre-de-Haut and eighteen for Terre-de-Bas. The islands share only ten significant plants uses and four of them have notable different frequencies. The informant consensus factor in the use of many specific remedies was fairly high, that gave an additional validity to these popular medicines. CONCLUSION: The data presented in this study show that popular knowledge on medicinal plants uses is still alive in the studied area. The difference between the two nearby islands is very narrow but on the other hand, there exist some differences possibly due to a probable declining of plant resources and a more important flux of migration and its provision of other practices of healthcare in Terre-de-Haut.

Patterns of variability in the diameter of lateral roots in the banana root system.

The relative importance of root system structure, plant carbon status and soil environment in the determination of lateral root diameter remains unclear, and was investigated in this study. Banana (Musa acuminata) plants were grown at various moderate levels of soil compaction in two distinct experiments, in a field experiment (FE) and in a glasshouse experiment (GE). Radiant flux density was 5 times lower in GE. The distribution of root diameter was measured for several root branching orders. Root diameters ranged between 0.09 and 0.52 mm for secondary roots and between 0.06 and 0.27 mm for tertiary roots. A relationship was found between the diameter of the parent bearing root and the median diameter of its laterals, which appears to be valid for a wide range of species. Mean lateral root diameter increased with distance to the base of the root and decreased with branching density [number of lateral roots per unit length of bearing root (cm(-1))]. Typical symptoms of low light availability were observed in GE. In this case, lateral root diameter variability was reduced. Although primary root growth was affected by soil compaction, no effects on lateral root diameter were observed.

Number, position, diameter and initial direction of growth of primary roots in Musa.

To understand soil colonization by a root system, information is needed on the architecture of the root system. In monocotyledons, soil exploration is mainly due to the growth of adventitious primary roots. Primary root emergence in banana was quantified in relation to shoot and corm development. Root emergence kinetics were closely related to the development of aerial organs. Root position at emergence on the corm followed an asymptotic function of corm dry weight, so that the age of each root at a given time could be deduced from its position. Root diameter at emergence was related to the position of the roots on the corm, with younger roots being thicker than older ones. However, root diameters were not constant along a given root, but instead decreased with the distance to the base; roots appear to be conical in their basal and apical parts. Root growth directions at emergence were variable, but a high proportion of the primary roots emerged with a low angle to the horizontal. Further research is needed to evaluate whether these initial trajectories are conserved during root development. Results presented in this study are in good agreement with those reported for other monocotyledons such as maize and rice. They give quantitative information that will facilitate the development of models of root system architecture in banana.