Do smallholder farmer-led seed systems have the capacity to supply good-quality, fungal-free sorghum seed?

Local seed systems that are developed, managed and maintained by farmers are a fundamental practice in smallholder crop production, supporting more than 80% of farmers in sub-Saharan Africa and feeding more than 70% of its population. The resilience of such systems is under threat from poverty, climate change, drought, increased pests and diseases, over-promotion of modern crop varieties, change of lifestyles and restrictive seed policies. The system continues to be maligned as having inferior quality, yet few studies support this assertion. This study aims to fll this research gap by evaluating 60 sorghum seed samples collected from smallholder farmers in Uzumba-MarambaPfungwe and Chimanimani districts of Zimbabwe. We investigated the efect of farmer-led seed management practices (e.g. seed acquisition and seed storage practices) on farm-derived sorghum seed quality (moisture, germination and fungal incidences). We found farmers using diverse seed sources and seed storage practices. Seeds were typically of good quality in that their storage moisture content was low, their germination was high, and fungal incidences were low. Seed sourced from local markets, non-governmental organizations and other farmers had germination and moisture standards that met the sorghum certifcation standards in Zimbabwe. However, few samples obtained from the relatives and government failed to meet the germination and/or moisture certifcation standards. We detected low incidences of fungi (Aspergillus favus, Aspergillus niger, Curvularia lunata, Fusarium sp. and Penicillium sp.) in sorghum seed samples tested and in particular Fusarium sp., which is the most economic important fungus in sorghum production. We conclude that farmer-led seed systems have the capacity to supply seeds of good quality and recommend that such systems should be recognized and promoted to meet the ever-evolving needs of smallholder farmers in sub-Saharan Africa

Naturally occurring bioactive compounds from four repellent essential oils against Bemisia tabaci whiteflies

BACKGROUNDIn tropical countries, netting is an effective sustainable tool for protecting horticultural crops against Lepidoptera, although not against small pests such as Bemisia tabaci, while smaller mesh netting can be used in temperate regions. A solution is to combine a net with a repellent. Previously we identified repellent essential oils: lemongrass (Cymbopogon citratus), cinnamon (Cinnamomum zeylanicum), cumin (Cuminum cyminum) and citronella (Cymbopogon winternarius). The present study was designed to identify the active compounds of these essential oils, characterise their biological activity and examine their potential for coating nets. We investigated the efficiency and toxicity of nets dipped in different solutions. We then studied the repellent effect with an olfactometer and the irritant effect by videotracking. RESULTSGeraniol and citronellol were the most promising net coatings owing to their repellent effect. The repellency, irritancy or toxicity varied with the product and concentration, and these features were independent, indicating that the repellent and the irritant/toxic mechanisms were not the same. The combined effects of these different compounds account for the bioactivity of the mixture, suggesting interactions between the compounds. CONCLUSIONThis new sustainable strategy for protecting vegetable crops against whiteflies is discussed, in addition to the use of companion plants that could produce such bioactive compounds

Electrophysiological and behavioral characterization of bioactive compounds of the Thymus vulgaris, Cymbopogon winterianus, Cuminum cyminum and Cinnamomum zeylanicum essential oils against Anopheles gambiae and prospects for their use as bednet treatments

Background: Laboratory and field studies showed that repellent, irritant and toxic actions of common public health insecticides reduce human-vector contact and thereby interrupt disease transmission. One of the more effective strategies to reduce disease risk involves the use of long-lasting treated bednets. However, development of insecticide resistance in mosquito populations makes it imperative to find alternatives to these insecticides. Our previous study identified four essential oils as alternatives to pyrethroids: Thymus vulgaris, Cymbopogon winterianus, Cuminum cyminum, Cinnamomum zeylanicum. The objectives of this study were to identify active compounds of these essential oils, to characterize their biological activity, and to examine their potential as a treatment for bednets. Methods: We evaluated the electrophysiological, behavioural (repellency, irritancy) and toxic effects of the major compounds of these oils against Anopheles gambiae strain 'Kisumu'. Results: Aldehydes elicited the strongest responses and monoterpenes the weakest responses in electroantennogram (EAG) trials. However, EAG responses did not correlate consistently with results of behavioral assays. In behavioral and toxicity studies, several of the single compounds did exhibit repellency, irritancy or toxicity in An. gambiae; however, the activity of essential oils did not always correlate with activity expected from the major components. On the contrary, the biological activity of essential oils appeared complex, suggesting interactions between individual compounds and the insect under study. Data also indicated that the three effects appeared independent, suggesting that repellency mechanism(s) may differ from mechanisms of irritancy and toxicity. Conclusions: Based on the bioassays reported here, some of the compounds merit consideration as alternative bednet treatments

Push-pull strategy combined with net houses for controlling cowpea insect pests and enhancing crop yields

Published online: 25 Nov 2020Net houses can be used in tropical environments to protect crops such as cowpea against large insect pests, thereby avoiding pesticide treatments while sustainably mitigating the effects of climate change. We investigated a push-pull strategy to prevent small insect pest outbreaks in a net house. The push component consisted of two stimulus plants, i.e. Cymbopogon citratus and Tagetes minuta, and the pull stimuli consisted of visual cues from blue and yellow sticky traps. Field experiments were set up in central Kenya and conducted during a rainy and a dry season, involving an open field control treatment, and three management treatments consisting of (1) an open field push-pull treatment, (2) a net house treatment and (3) a combined net house + push-pull treatment. Trialeurodes vaporariorum infestations were lower in the net house and net house + push-pull treatments than in the two open field treatments during the dry period or in the control treatment during the rainy period. Aphis craccivora infestations were higher in the net house and net house + push-pull treatments than in the control and open field push-pull treatments during the dry period, while no differences were observed among treatments during the rainy period. Megalurothrips sjostedti infestations did not vary among treatments in both periods. Among the larger insect pests, Clavigralla tomentosicollis infestations were lower in the net house and net house + push-pull treatments than in the open field treatments during the dry period, while Maruca vitrata infestations were lower in the net house treatment than in the control. During the rainy period, C. tomentosicollis infestations were higher in the net house + push-pull treatment than in the net house treatment, whereas M. vitrata infestations did not vary among treatments. Compared to the control, Empoasca sp. infestations were lower in the net house and net house + push-pull treatments in both periods, and in the open field push-pull treatment in the rainy period. Cowpea pod and grain yield and quality were higher in the net house and net house + push-pull treatments than in the control irrespective of the period. Although the treatments 1 reduced some of the pests, the net house and net house + push-pull treatments were effective in protecting cowpeas against most of the pests while improving pod yields in both periods

Comparison of biological methods to control Aphis fabae Scopoli (Hemiptera: Aphididae) on kalanchoe crops in East Africa

Published online: 21 Dec 2020Aphids cause considerable damage to numerous crops all over the world and insecticides are the main means of controlling them, despite their detrimental impacts on human and environmental health. This study assessed the effectiveness of the parasitoid Aphidius colemani Viereck (Hymenoptera: Braconidae), a mixture of predatory ladybird beetles, Hippodamia variegata Goeze, Chilocorus calvus Chiccl, and Cheilomenes propinqua Mulsant (Coleoptera: Coccinellidae), and an entomopathogenic strain of Aspergillus flavus Link (Eurotiales: Trichocomaceae), collected locally in Tanzania, to control Aphis fabae Scopoli (Hemiptera: Aphididae). After assessing the predation and parasitism rates of these natural enemies at different aphid densities in laboratory experiments, their ability to control aphids on kalanchoe was assessed in a greenhouse experiment over two seasons. The largest number of A. fabae parasitized or consumed in the laboratory was found at a density of 160 aphids per predator, or parasitoid. At that density, an adult female of A. colemani parasitized 114 A. fabae per day, on average, and adults of C. calvus, H. variegata, and C. propinqua consumed 75, 72, and 85 aphids per day, respectively. A. flavus spores applied at 1 × 107 spores ml−1 reduced the aphid population by 7.9 and 12.6 times within 10 days in the first and second seasons of the greenhouse experiments, respectively, as opposed to 2.8 and 2.5 times by releasing a mixture of the ladybirds at a rate of 5 adults/m2, and by 3.3 and 9.5 times by releasing A. colemani at a rate of 2 adults/m2. This study confirmed the potential of these locally collected bio-control agents for controlling A. fabae. However, use of the isolated A. flavus strain was undermined by its production of aflatoxin. Further research is therefore required to tap into the potential of a non-toxic strain of A. flavus and/or other entomopathogenic fungi

Repellent, irritant and toxic effects of 20 plant extracts on adults of the malaria vector Anopheles gambiae mosquito

Pyrethroid insecticides induce an excito-repellent effect that reduces contact between humans and mosquitoes. Insecticide use is expected to lower the risk of pathogen transmission, particularly when impregnated on long-lasting treated bednets. When applied at low doses, pyrethroids have a toxic effect, however the development of pyrethroid resistance in several mosquito species may jeopardize these beneficial effects. The need to find additional compounds, either to kill disease-carrying mosquitoes or to prevent mosquito contact with humans, therefore arises. In laboratory conditions, the effects (i. e., repellent, irritant and toxic) of 20 plant extracts, mainly essential oils, were assessed on adults of Anopheles gambiae, a primary vector of malaria. Their effects were compared to those of DEET and permethrin, used as positive controls. Most plant extracts had irritant, repellent and/or toxic effects on An. gambiae adults. The most promising extracts, i. e. those combining the three types of effects, were from Cymbopogon winterianus, Cinnamomum zeylanicum and Thymus vulgaris. The irritant, repellent and toxic effects occurred apparently independently of each other, and the behavioural response of adult An. gambiae was significantly influenced by the concentration of the plant extracts. Mechanisms underlying repellency might, therefore, differ from those underlying irritancy an

Seed exchange networks for agrobiodiversity conservation. A review

The circulation of seed among farmers is central to agrobiodiversity conservation and dynamics. Agrobiodiversity, the diversity of agricultural systems from genes to varieties and crop species, from farming methods to landscape composition, is part of humanity�s cultural heritage. Whereas agrobiodiversity conservation has received much attention from researchers and policy makers over the last decades, the methods available to study the role of seed exchange networks in preserving crop biodiversity have only recently begun to be considered. In this overview, we present key concepts, methods, and challenges to better understand seed exchange networks so as to improve the chances that traditional crop varieties (landraces) will be preserved and used sustainably around the world. The available literature suggests that there is insufficient knowledge about the social, cultural, and methodological dimensions of environmental change, including how seed exchange networks will cope with changes in climates, socio-economic factors, and family structures that have supported seed exchange systems to date. Methods available to study the role of seed exchange networks in the preservation and adaptation of crop specific and genetic diversity range from meta-analysis to modelling, from participatory approaches to the development of bio-indicators, from genetic to biogeographical studies, from anthropological and ethnographic research to the use of network theory. We advocate a diversity of approaches, so as to foster the creation of robust and policy-relevant knowledge. Open challenges in the study of the role of seed exchange networks in biodiversity conservation include the development of methods to (i) enhance farmers� participation to decision-making in agro-ecosystems, (ii) integrate ex situ and in situ approaches, (iii) achieve interdisciplinary research collaboration between social and natural scientists, and (iv) use network analysis as a conceptual framework to bridge boundaries among researchers, farmers and policy makers, as well as other stakeholders