Étude de la diversité génétique au sein des génomes nucléaire et chloroplastique chez les cinq races connues du Striga gesnerioides, une plante parasite d'importance mondiale

La présente recherche avait pour but de révéler la diversité génétique qui existe au sein et entre différentes populations d’Afrique de l’Ouest du parasite épirhize Striga gesnerioides. Cette plante parasite plusieurs espèces appartenant à différentes familles de dicotylédones, dont le niébé (Vigna unguiculata), une légumineuse alimentaire constituant la majeure partie des protéines retrouvées dans la diète de plusieurs populations rurales des zones semi-arides d’Afrique de l’Ouest. Certains cultivars résistants ont déjà été identifiés et sont utilisés dans les programmes d’amélioration variétale. Il existe cependant plusieurs biotypes, ou races physiologiques, de S. gesnerioides, lesquels diffèrent quant à leur virulence. En utilisant trois types de marqueurs moléculaires différents, soit des marqueurs AFLP, ISSR et cpSSR, nous avons mis en évidence la quasi-absence de variabilité au sein des populations de Striga étudiées, ainsi que la très faible diversité qui existe entre les différentes populations du parasite. Nous n’avons pas non plus trouvé de marqueurs permettant de discriminer entre les races. Il semble exister une certaine structure dans la distribution géographique des populations, mais aucun groupe monophylétique n’a été obtenu sur une base « raciale », indiquant que la virulence ne joue pas encore un rôle dans leur différentiation. Quelques hypothèses ont été émises pour expliquer la faible diversité et l’absence de marqueur de races, dont le mode de reproduction autogame du parasite, ainsi qu’une origine probablement récente de la forme de Striga gesnerioides parasitant le niébé.The goal of the present study was to reveal the genetic diversity within and among different West African populations of the root parasite Striga gesnerioides. This plant parasitizes many species from different dicotyledonous families, including cowpea (Vigna unguiculata), an important legume crop and the major dietary protein source for many people of the semi-arid regions of West Africa. Some resistant cowpea varieties have been identified and are used in breeding programs. However, based on host-parasite interactions in the field, various races of S. gesnerioides attacking cowpea have been identified. Using three different types of molecular markers, AFLP, ISSR and cpSSR, we showed that there is almost no genetic variability within populations. The variability between the populations was also extremely low and did not allow discrimination of the five races. A few populations were more closely related, and there was a certain geographical structure but no “racial” clustering could be seen, enhancing the fact that virulence is not yet involved in the genetic differentiation process. Possible causes of the extremely low level of genetic variability seen in S. gesnerioides are proposed including the autogamous mode of reproduction of the parasite and the hypothesis that the cowpea strain has only quite recently arisen

Striga (Witchweeds) in Sorghum and Millet: Knowledge and Future Research Needs

Striga spp (witchweeds), are notorious root hemiparasites on cereal and legume crops grown in the semi-arid tropical and subtropical regions of Africa, the southern Arabian Peninsula, India, and parts of the eastern USA. These weed-parasites cause between 5 to 90% losses in yield; total croploss data have been reported. Immunity in hosts has not been found. Past research activities and control methods for Striga are reviewed, with emphasis on the socioeconomic significance of the species. Striga research involving biosystematics, physiological biochemistry, cultural and chemical control methods, and host resistance are considered. We tried to itemize research needs of priority and look into the future of Striga research and control In light of existing information, some control strategies which particularly suit subsistence and emerging farmers' farming systems with some minor adjustments are proposed. The authors believe that a good crop husbandry is the key to solving the Striga proble

Breeding cowpea (Vigna unguiculata [L.] Walp) for improved yield and related traits using gamma irradiation.

Doctor of Philosophy in Plant Breeding. University of KwaZulu-Natal, Pietermaritzburg 2016.Cowpea is an important grain legume widely grown in sub-Saharan Africa for food and feed. In Namibia cowpea productivity is considerably low due to a wide array of abiotic and biotic stresses and socio-economic constrains. The overall objective of this study was to develop farmers’ preferred cowpea varieties with enhanced grain yield and agronomic traits through mutation breeding. The specific objectives of the study were to: (1) assess farmers’- perceived production constraints, preferred traits and the farming system of cowpea, and its implication for breeding in northern Namibia, (2) determine an ideal dose of gamma radiation to induce genetic variation in selected cowpea genotypes, (3) identify desirable cowpea genotypes after gamma irradiation of three IITA acquired cowpea varieties widely grown in Namibia including Nakare (IT81D-985), Shindimba (IT89KD-245-1) and Bira (IT87D-453-2) through continuous selections from M2 through M6 generations, (4) determine G x E interaction and yield stability of elite mutant cowpea selections and to identify promising genotypes and representative test and production environments, and (5) select elite cowpea varieties that meet farmers’ needs and preferences through farmers’ participation and indigenous knowledge. Participatory rural appraisal (PRA) study was conducted across four selected regions of northern Namibia including Kavango East, Kavango West, Oshikoto and Omusati where cowpea is predominantly cultivated involving 171 households. The majority of respondent farmers (70.2%) grow local unimproved cowpea varieties. About 62.6% of interviewed farmers reported low yields of cowpea varying from 100-599 kg/ha, while 6% of respondents achieved good grain harvests of 1500-1999 kg/ha. Farmers who grow local unimproved avarieties also indicated that the local varieties were not readly available and most have lost them to prolonged droughts and poor rainfall. Most farmers (59.1%) produced cowpea for home consumption, while 23.4% indicated its food and market value. Field pests such as aphids (reported by 77.8% respondents), leaf beetles (53.2%) and pod borers (60%) and bruchids (100%) were the major constraints. Striga gesnerioides and Alectra Vogelii (Benth) were the principal parasitic weeds reported by 79.5% respondent farmers. Soil fertility levels were reported to be very low across regions and all farmers did not apply any fertilizers on cowpea. Farmers-preferred traits of cowpea included a straight pod shape (reported by 61.4% respondents), a long pod size bearing at least 10 seeds (68.4%), white grain colour (22.2%) and high above ground biomass (42.1%). Inter-cropping of cowpea with sorghum or pearl millet was the dominant cowpea farming system in northern Namibia. About 68.4% of farmers used a relatively smaller proportion of their land (<1 ha) for cowpea production, while only 9.9% allocated more than 5 ha-1. Before a large scale mutagenesis an appropriate dose of radiation should be established on target genotypes. Therefore, seeds of the following three cowpea genotypes widely grown in Namibia: Nakare (IT81D-985), Shindimba (IT89KD-245-1) and Bira (IT87D-453) were gamma irradiated using seven doses (0, 100, 200, 300, 400, 500 and 600 Gy) at the International Atomic Energy Agency, Austria. The optimum doses at LD50 for the genotypes Nakare and Shindimba were 150 and 200 Gy, respectively while genotype Bira tolerated high dose of 600 Gy. Using linear regression model, the LD50 for genotypes Nakare, Shindimba and Bira were established to be 165.24, 198.69 and 689 Gy, respectively. Large scale mutagenesis were undertaken through gamma irradiation using seeds of the three varieties (Nakare, Shindimba and Bira). Field experiments were conducted in order to identify agronomically desirable cowpea genotypes. Substantial genetic variability was detected among cowpea genotypes after mutagenesis across generations including flowering ability, maturity, flower and seed colours and grain yields. Overall 34 elite cowpea mutants were selected from 37 genotypes including 3 parental lines showing phenotypic and agronomic stability. The selected 34 promising mutant lines along with the 3 parents were recommended for adaptability and stability tests across representative agro-ecologies for large-scale production or breeding in Namibia. The lines were subjected to G x E study conducted at three selected sites (Bagani, Mannheim and Omahenene) and two cropping seasons (2014/2015 and 2015/2016) providing six environments. The following four promising mutant genotypes: G9 (ShL3P74), G10 (ShR3P4), G12 (ShR9P5) and G4 (ShL2P4) were identified with better grain yields of 2.83, 2.06, 1.99 and 1.95, t.ha-1, in that order. The parental lines designated as G14 (Shindimba), G26 (Nakare) and G37 (Bira) provided mean grain yields of 1.87, 1.48 and 1.30 t.ha-1, respectively. The best environments in discriminating the test genotypes were Bagani during 2014/15 and Omahenene during 2014/15. Participatory cowpea varietal selection was undertaken in the northern Namibia using a set of newly developed 34 elite cowpea varieties. Genotypes were evaluated along with the three parents. Field evaluations were conducted across three selected villages in Omusati Region of northern Namibia where the crop is predominantly cultivated. Test varieties were independently assessed and scored using nine agronomic traits involving 114 participating farmers. Overall, the following 10 farmers-preferred cowpea varieties were selected: R9P5 (Sh200), R3P4 (Sh100), R4P1 (Sh100), L3P74 (Sh100), R1P12 (Nk100), R8P9 (Nk150), R5P1 (Nk150), R2P9 (Nk150), R10P5 (Nk150) and R11P2 (Bi600) for their larger seed size, white grain colour, high pod setting ability, insect pest tolerance, early maturity, longer pod size, drought tolerance, high biomass and pod yields. Generally, the study identified valuable cowpea mutants derived from three local varieties Shindimba, Bira and Nakare using gamma irradiation. The identified genotypes are phenotypically and agronomically stable and recommended to distinct, uniformity and stability (DUS) trials for varietal registration and release in northern Namibia

Enquête Ethnobotanique Sur La Prise En Charge Traditionnelle De L’infertilité Féminine Dans La Région Sanitaire Des Savanes Au Togo

Introduction: The management of female infertility by the conventional medicine is very expensive and its coast is unavailable for the very poor populations. In Africa, an important recourses of medicinal plants are available for health care. Objective: The present study was led to recorder traditional remedies use to treat female infertility in the Sanitary Savannas Region of Togo. Methodology: For data collection, semi interview was used. Data were processed and analysed using ethnobotanical quantitative index. The Selection by Progressive Elimination (SPE) was essentially used for the choice of species. Results: With 51 practitioners interviewed, 79 recipes constituted by 87 species belonging to 48 botanical families were collected. Combretaceae (12,64 %) and Rubiaceae (5,7 %) were the most frequent families. Trees (36,78 %) and shrubs (27,58%) were the main ports. Roots (29,17 %) and leaves (27,5 %) were the most used parts. Recipes were prepared frequently by decoction (51,88 %) and powder (38,12%), and were principally taken orally (47,28 %) and by body bath (43,48 %). Sexually transmitted infections (STI) (143 citations) and Painful menstruations (PM) (108 citations) were the most frequent pathologies. The highest Informants consensus factors were 0,61 and 0,56 respectively for STI and PM. The most important Fidelity degrees was 25,49 % for STI related to Capsicum frutescens and Piper guineense. Related to Aframomum melegueta, Piper guineense and Zanthoxylum zanthoxyloides the Fidelity degree was 19,61% for PM and STI. Blighia sapida, Ganoderma colossus, Kigelia africana and Mangifera indica were selected. Conclusion: Plants with highest fidelity degree and those selected by SPE will be subjected to laboratory tests

Molecular Studies on Sunflower Broomrape (Orobanche cumana Wallr.)

Los jopos (Orobanche spp. y Phelipanche spp.) son un grupo de aproximadamente 170 especies de plantas holoparásitas distribuidas principalmente en el Hemisferio Norte. A pesar de que la mayor parte de Orobanche spp. sólo parasitan plantas silvestres, algunas de ellas se han convertido en malas hierbas nocivas en un rango variable de cultivos. Orobanche cumana Wallr. se distribuye de forma natural desde Asia Central hasta el sudeste de Europa, dónde parasita especies silvestres de la familia Asteraceae. La costa del Mar Negro en el este de Bulgaria es una de las principales áreas naturales de distribución de O. cumana, dónde esta especie se encuentra principalmente parasitando Artemisia maritima L. Esta especie, conocida como jopo del girasol (Helianthus annuus L.), es también una importante mala hierba parásita de este cultivo, dónde fue observada por primera vez parasitando girasol en Rusia en la década de 1890. Orobanche cumana está presente en los cultivos de girasol en muchos países de todo el mundo, especialmente en el centro y este de Europa, España, Turquía, Israel, Rusia, Ucrania, Irán, Kazajstán, China, Francia y Túnez. En la mayoría de estas áreas, O. cumana causa severas pérdidas de rendimiento en los cultivos de girasol. Orobanche cumana se encuentra en España como una especie alóctona que parasita al girasol cultivado exclusivamente, a diferencia de la especie estrechamente relacionada O. cernua L., que es una especie autóctona que sólo parasita huéspedes silvestres de la familia Asteraceae, principalmente Artemisia spp. Durante muchos años, O. cumana se distribuyó en el Valle del Guadalquivir (Andalucía, Sur de España) y en la provincia de Cuenca (Catilla-La Mancha, Centro de España), pero en los últimos años, se ha extendido a otras áreas de cultivo de ambas zonas y en nuevos campos de otras regiones como Castilla y León (Norte de España). La información sobre la diversidad genética, la dinámica de poblaciones, el sistema de reproducción, el flujo genético y la genética de la virulencia en O. cumana es escasa, especialmente en relación con el análisis molecular entre y dentro de las poblaciones, debido a la falta de marcadores moleculares adecuados para este tipo de estudios. Sólo unos pocos estudios moleculares se han llevado a cabo en O. cumana, limitados a la evaluación de la diversidad genética a través de isoenzimas o marcadores RAPD. Además, sólo algunos estudios se han descrito sobre las interacciones genéticas entre formas silvestres y de malas hierbas de especies de plantas parásitas. La aplicación de estos estudios es importante para el desarrollo de estrategias de mejora para el control a largo plazo que implica la resistencia genética en girasol. Por otra parte, el conocimiento de las interacciones entre los genotipos silvestres y de malas hierbas de las plantas parásitas es importante porque la vegetación silvestre puede jugar un papel como reservorio de diversidad genética para la superación de los mecanismos de resistencia genética en los cultivos huéspedes. Pero, por otro lado, la evolución de la virulencia en las poblaciones de malas hierbas parásitas también puede tener un impacto sobre la distribución de las especies en la naturaleza. Unido a esto, se necesitan marcadores alternativos como marcadores microsatélites (SSRs) que son reproducibles, no influenciados por el ambiente, multialélicos y codominantes, para permitir análisis más efectivos en O. cumana. Dado que los estudios sobre la variabilidad genética de poblaciones de O. cumana se han basado en un número restringido de poblaciones recolectadas en girasol y tipos de marcadores, una evaluación a mayor escala podría contribuir a una mejor comprensión de la estructura genética y dinámica de la especie. Tampoco hay información sobre la estructura genética de poblaciones de O. cumana que parasitan especies silvestres y su relación con las poblaciones de malas hierbas parásitas en zonas en las que conviven, y su virulencia en girasol. Como los recursos disponibles para estudios moleculares con...Broomrapes (Orobanche spp. and Phelipanche spp.) are a group of around 170 holoparasitic plant species mainly distributed in the Northern Hemisphere. Even though most of the Orobanche spp. only parasitize wild plants, some of them have become noxious weeds on a variable range of cultivated hosts. Orobanche cumana Wallr. is naturally distributed from Central Asia to Southeastern Europe, where it parasitizes wild Asteraceae species. The Black Sea coast in Eastern Bulgaria is one of the main natural distribution areas for O. cumana, where this species is mainly found parasitizing Artemisia maritima L. This species, known as sunflower broomrape, is also an important parasitic weed of sunflower (Helianthus annuus L.), where it was first observed parasitizing this crop in Russia in the 1890s. Orobanche cumana is present in sunflower crops in many countries around the world, especially in Central and Eastern Europe, Spain, Turkey, Israel, Russia, Ukraine, Iran, Kazakhstan, China, France and Tunisia. In most of these areas, O. cumana causes severe yield losses in sunflower crops. Orobanche cumana is found in Spain as an allochthonous species parasitizing exclusively cultivated sunflower, in contrast to the closely related species O. cernua L., which is an autochthonous species that only parasitizes wild Asteraceae hosts, mainly Artemisia spp. For many years, O. cumana was distributed in the Guadalquivir Valley (Andalucía, Southern Spain) and Cuenca province (Castilla-La Mancha, Central Spain), but in recent years, it has spread to other areas of these both cultivation regions and new fields in other regions such as Castilla y León (Northern Spain). Information on genetic diversity, population dynamics, mating system, gene flow and virulence genetics in O. cumana is scarce, particularly concerning molecular analysis among and within populations, due to the lack of suitable molecular markers for such studies. Only a few molecular studies have been conducted in O. cumana, restricted to evaluating genetic diversity through isoenzymes or RAPD markers. Furthermore, only some studies have been described on genetic interactions between wild and weedy forms of parasitic plant species. The application of these studies is important for the development of long-term breeding strategies for control involving genetic resistance in sunflower. Moreover, knowledge about interactions between wild and weedy genotypes of parasites is significant because wild vegetation may play a role as reservoir of genetic diversity for overcoming genetic resistance mechanisms in the host crops. But on the other hand, evolution of virulence in weedy populations may also have an impact on the distribution of the species in the wild. Coupled with this, alternative markers such as Simple Sequence Repeat (SSR) markers, which are reproducible, neutrally evolving, multiallelic and co-dominant, are needed to enable more powerful analyses in O. cumana. Since studies on genetic variability of O. cumana populations have been based on restricted numbers of weedy populations collected on sunflower and marker types, a larger-scale evaluation would contribute to a better understanding of genetic structure and dynamics of this species. There is also no information on the population structure of O. cumana populations parasitizing wild species and their genetic relationship with weedy populations in areas where they co-exist, and their virulence on sunflower. As very limited SSR resources are available for molecular research in O. cumana and other Orobanche spp., we developed and characterized a collection of SSR primer pairs for sunflower broomrape. Four thousand two hundred SSR-containing candidate sequences were obtained from O. cumana using Next Generation Sequencing (454 GS-FLX Titanium), from which 298 SSR primer pairs were designed and 217 of them used for validation. Seventy nine SSR primers produced reproducible, high quality amplicons of the expected size that were polymorphic among 18 O

Pflanzenvielfalt in Burkina Faso : Analyse, Modellierung und Dokumentation

Um die Biodiversität Burkina Fasos darzustellen und auszuwerten, wurden umfangreiche Diversitätsdaten aus Sammlungsbelegen, Vegetationsaufnahmen und Literatur zusammengestellt. Die eigene Datenerhebung während dreier Feldaufenthalte hat mit > 300 Vegetationsaufnahmen (einschließlich der Biodiversitätsobservatorien) und > 1200 Herbarbelegen dazu beigetragen. Die Verwendung von relationalen Datenbanken (Microsoft Access) und GIS ermöglichte eine umfassende Analyse dieser enormen Datenmengen (> 100 000 Verbreitungspunkte) unter Einbeziehung von weiteren Art- oder ortsgebundenen Informationen. Datenbankstrukturen und Prozeduren wurden zu einem großen Teil selbst entwickelt. Unregelmäßigkeiten in den Primärdaten konnten durch Artverbreitungsmodelle ausgeglichen werden, die rasterbasierte Umweltdaten verwenden, insbesondere Satellitenbilder, Klima- und Höhendaten. Für die zusammenfassenden Analysen (Artenreichtum nach Familie, Lebensform, Photosynthesetyp; turnover) mussten wiederum eigene Prozeduren entwickelt werden. Räumliche Muster der Biodiversität wurden im landesweiten Rahmen, wie auch lokal für die Regionen Oudalan und Gourma, dargestellt. Die Zusammenfassung der Flora nach taxonomischen und ökologischen Gruppen gewährt dabei Einblicke in ökologische Zusammenhänge und die Eignung einzelner Gruppen als Indikatoren. Deutlich zeigen sich die Veränderungen des Lebensformspektrums und des Artenreichtums sowohl auf Landesebene im Zusammenhang mit dem Makroklima als auch in einer detaillierten Analyse des Oudalan – wo der Einfluss von Boden und Relief deutlich wird. Die großräumigen Muster der Artenvielfalt sind hauptsächlich durch klimatische Faktoren geprägt, auch der menschliche Einfluss ist in Form verschiedener Nutzungsformen vom Klima abhängig und schwer davon zu trennen. Umso deutlicher werden die Folgen intensiver Landnutzung aber in den Detailstudien der nordsudanischen Biodiversitätsobservatorien und des sahelischen Wiederbegrünungsprojektes. Über die in diesem Rahmen dargestellten Ergebnisse hinaus ergeben sich insbesondere aus der umfassenden Datenbasis und der interdisziplinären Zusammenarbeit mit Fernerkundung und Ethnobotanik weitere vielversprechende Möglichkeiten. Unter anderem wird auf der Grundlage der Datenbanken und ergänzender Literaturrecherchen eine aktualisierte Checklist der Gefäßpflanzen Burkina Fasos erstellt und eine Revision der phytogeographischen Zonen für Burkina Faso ist geplant

Molecular perspectives on the ecologically inconsistent effectiveness of the mycoherbicide Fusarium oxysporum f. sp. strigae against Striga hermonthica

Cereals are a major staple that is crucial for food security in sub-Saharan Africa (SSA). Sadly, the obligate hemiparasitic witchweed, Striga spp., especially Striga hermonthica (Delile) Benth., is a major biotic constraint to cereal production in SSA, causing enormous crop yield losses estimated at US$10 billion annually. Fusarium oxysporum f. sp. strigae (Fos) is the most renowned fungal biological control agent (BCA) for specifically and significantly tackling S. hermonthica under agricultural systems. Field surveys, however, have revealed the inconsistent effectiveness of Fos isolates against S. hermonthica in differing zones of SSA (i.e., West Africa, East Africa). This daunting phenomenon is a critical challenge that affects Fos reliability and deters its use for S. hermonthica management. The inconsistent effectiveness of Fos against S. hermonthica was presumably ascribed to the interactions that occur between the differing location-specific ecological factors of the pathosystem i.e., abiotic (climate, moisture, or soil physico-chemistry) or biotic (S. hermonthica, Fos isolate, or the plant microbiome). Without doubt, the diversity of a host or pathogen is a primary determinant of the innate susceptibility or virulence of the host or pathogen, respectively. In terms of S. hermonthica diversity, genomic variation of individuals, or regional genetic variation of the sampling zone, were the two major forces suspected. However, the important determiner out of the two forces was unknown. Besides, despite the suppression/death that Fos causes to S. hermonthica, the physiological damage S. hermonthica initiates to an infested cereal crop is mostly irreversible. Hence, in examining strategies for circumventing the main problem of Fos inconsistent effectiveness against S. hermonthica, and the physiological consequences of S. hermonthica on the host cereal crop, the integration of other (non-Fos inoculum) BCA were suggested as possible means for improving the efficiency of S. hermonthica biocontrol. For example, by utilizing a bioherbicide cocktail of Fos and plant growth promoting rhizobacteria (PGPR), or Striga seed germination-inhibiting fungal toxins. Apart from the popular reputation of PGPR in enhancing crop health and growth, certain PGPR strains (especially Bacillus subtilis isolate GB03) have been earlier reported for their highly-promising potential of antagonizing S. hermonthica development. Similarly, certain fungal extracellular metabolites (exometabolites), especially of Fusarium origin, were reported to completely inhibit S. hermonthica seed germination in vitro at very low concentrations (&#8804; 1 mM). Unfortunately, knowledge of the microbe (Fos)microbe (PGPR) interaction, their localization and ecological niche, for enabling their expected synergistic impact of simultaneously suppressing S. hermonthica and enhancing the Striga-infected cereal crop biomass, was unknown. Also, it was unknown if highly potent/efficient Striga seed germination-inhibiting fungal exometabolites will consistently suppress S. hermonthica in planta. Thus, in the context of genetic diversity in S. hermonthica, the PhD study focused on gaining (molecular) insights into the inconsistent effectiveness of Fos against S. hermonthica; including the examination of some strategies for improving S. hermonthica biocontrol efficiency, precisely by integrating PGPR, or Striga seed germination-inhibiting Fusarium exometabolites, into a S. hermonthica biocontrol system. The first research examined the molecular genetic basis, underlying the variable susceptibility of S. hermonthica populations sampled from differing zones of SSA (West Africa, East Africa) to contrasting Fos isolates (Foxy-2, FK3). Regardless of sampling zone, the S. hermonthica populations displayed divergent susceptibility patterns to the Fos isolates i.e., a S. hermonthica class was susceptible to both Foxy-2 and FK3, while the other class was susceptible to either Foxy-2 or FK3. This manifestation correlated with nucleotide mutations at certain loci. Thus, genomic variation in S. hermonthica is a superior determinant of the inconsistent effectiveness of Fos isolates, rather than the S. hermonthica sampling zone. The second research examined the impact of coinoculating Fos and a PGPR (B. subtilis isolate GB03) into a S. hermonthica-sorghum parasitic system. Notwithstanding the colocalization of Fos and GB03 in common ecological niches of diseased S. hermonthica shoot (mainly in flavonoid-rich regions), GB03 thwarted Fos suppressive activity against S. hermonthica. Interestingly, a novel, alternative Fos entry route into S. hermonthica (through the trichome) was discovered. The coinoculation of Fos and GB03 presented no added advantage for S. hermonthica control. Finally, the third research screened a set of highly phytotoxic Fusarium exometabolites against S. hermonthica seed germination (in vitro) and incidence (in planta). This was to identify the most potent/efficient Fusarium exometabolite for S. hermonthica biocontrol. Among the tested exometabolites, diacetoxyscirpenol (DAS) was the most potent/efficient to completely suppress S. hermonthica both in vitro and in planta. Fos, however, did not produce DAS, due to underexpression of key genes necessary for Fusarium trichothecene biosynthesis. In conclusion, owing to the obligate outcrossing mating system in S. hermonthica, genomic variation is an inevitable phenomenon. This, therefore, plays a crucial role in the variable susceptibility of S. hermonthica to Fos. The newly discovered Fos (direct) entry route into S. hermonthica (trichome entry), elucidates a novel paradigm to the infection mechanism occurring under the S. hermonthica (host)Fos (pathogen) interaction, in addition to the previously reported indirect, rhizosphere-transmission. Thus, this novel phyllosphere-transmission, paves the way for further research that exploit this alternative Fos infection route for better S. hermonthica biocontrol. Lastly, considering the potency and broadscale efficacy against diverse S. hermonthica populations, the exometabolite DAS could serve as a new agent for a more efficient S. hermonthica biocontrol. Though, further examination of its specific mode of action against the target weed (S. hermonthica), as opposed to non-target organisms, is required.Getreide ist ein wichtiges Grundnahrungsmittel, das für die Ernährungssicherheit in Afrika südlich der Sahara (SSA) von entscheidender Bedeutung ist. Leider ist das obligate halbparasitäre Sommerwurzgewächs, Striga spp., insbesondere Striga hermonthica (Delile) Benth., eine große biotische Einschränkung für die Getreideproduktion in SSA und verursacht enorme Ernteverluste, die auf 10 Milliarden US-Dollar jährlich geschätzt werden. Fusarium oxysporum f. sp. strigae (Fos) ist der bekannteste pilzliche biologische Bekämpfungswirkstoff (BCA) zur spezifischen und signifikanten Bekämpfung von S. hermonthica in landwirtschaftlichen Systemen. Felduntersuchungen haben jedoch gezeigt, dass die Wirksamkeit von Fos-Isolaten gegen S. hermonthica in verschiedenen Zonen der SSA (d. h. Westafrika, Ostafrika) uneinheitlich ist. Dieses entmutigende Phänomen ist eine kritische Herausforderung, die die Zuverlässigkeit von Fos beeinträchtigt und seine Verwendung für die Bekämpfung von S. hermonthica verhindert. Die uneinheitliche Wirksamkeit von Fos gegen S. hermonthica wurde vermutlich auf die Wechselwirkungen zurückgeführt, die zwischen den verschiedenen standortspezifischen ökologischen Faktoren des Pathosystems auftreten, d. h. abiotischen (Klima, Feuchtigkeit oder physikalisch-chemische Eigenschaften des Bodens) oder biotischen (S. hermonthica, Fos-Isolat oder das Pflanzenmikrobiom). Zweifelsohne ist die Diversität eines Wirts oder Krankheitserregers eine der wichtigsten Determinanten für die angeborene Anfälligkeit bzw. Virulenz des Wirts oder Krankheitserregers. In Bezug auf die Diversität von S. hermonthica waren die genomische Variation der Individuen oder die regionale genetische Variation des Probenahmegebiets die beiden vermuteten Hauptfaktoren. Es war jedoch nicht bekannt, welcher der beiden Faktoren ausschlaggebend ist. Außerdem sind die physiologischen Schäden, die S. hermonthica an einer befallenen Getreidepflanze verursacht, trotz der Unterdrückung/Tötung von S. hermonthica durch Fos meist irreversibel. Bei der Untersuchung von Strategien zur Umgehung des Hauptproblems der unzureichenden Wirksamkeit von Fos gegen S. hermonthica und der physiologischen Folgen von S. hermonthica für die Wirtsgetreidekulturen wurde daher die Integration anderer BCA (ohne Fos-Inokulum) als mögliches Mittel zur Verbesserung der Effizienz der Biokontrolle von S. hermonthica vorgeschlagen. Zum Beispiel durch die Verwendung eines Bioherbizid-Cocktails aus Fos und pflanzenwachstumsfördernden Rhizobakterien (PGPR) oder von Pilztoxinen, die die Keimung von Striga-Samen hemmen. Abgesehen von dem guten Ruf, den PGPR bei der Förderung der Gesundheit und des Wachstums von Nutzpflanzen genießen, wurde bereits früher über das vielversprechende Potenzial bestimmter PGPR-Stämme (insbesondere des Isolats GB03 von Bacillus subtilis) zur Bekämpfung der Entwicklung von S. hermonthica berichtet. Ebenso wurde berichtet, dass bestimmte extrazelluläre Metaboliten von Pilzen (Exometaboliten), insbesondere von Fusarium, die Keimung von S. hermonthica-Samen in vitro bei sehr niedrigen Konzentrationen (&#8804; 1 mM) vollständig hemmen. Leider war das Wissen über die Interaktion zwischen Mikroben (Fos) und Mikroben (PGPR), ihre Lokalisierung und ökologische Nische nicht bekannt, um die erwartete synergistische Wirkung der gleichzeitigen Unterdrückung von S. hermonthica und der Verbesserung der Biomasse von Striga-infizierten Getreidepflanzen zu ermöglichen. Es war nicht bekannt, ob hochwirksame/effiziente, die Keimung von Striga-Samen hemmende, Pilzexometaboliten, dauerhaft S. hermonthica in planta unterdrücken können. Vor dem Hintergrund der genetischen Vielfalt von S. hermonthica konzentrierte sich die Doktorandenstudie daher auf die Gewinnung von (molekularen) Erkenntnissen über die uneinheitliche Wirksamkeit von Fos gegen S. hermonthica, einschließlich der Untersuchung einiger Strategien zur Verbesserung der Biokontroll-Effizienz von S. hermonthica, insbesondere durch die Integration von PGPR oder Striga-Samenkeimung hemmenden Fusarium Exometaboliten in ein S. hermonthica-Biokontrollsystem. Die erste Studie untersuchte die molekulargenetische Grundlage, die der unterschiedlichen Anfälligkeit von S. hermonthica-Populationen aus verschiedenen Zonen in SSA (Westafrika, Ostafrika) gegenüber unterschiedlichen Fos-Isolaten (Foxy-2, FK3) zugrunde liegt. Unabhängig von der Probenahmezone zeigten die S. hermonthica-Populationen unterschiedliche Empfindlichkeitsmuster gegenüber den Fos-Isolaten, d. h. eine S. hermonthica-Klasse war sowohl für Foxy-2 als auch für FK3 empfänglich, während die andere Klasse entweder für Foxy-2 oder für FK3 empfänglich war. Diese Erscheinung korrelierte mit Nukleotidmutationen an bestimmten Loci. Somit ist die genomische Variation in S. hermonthica ein entscheidenderer Faktor für die uneinheitliche Wirksamkeit von Fos-Isolaten als die S. hermonthica-Probenahmezone. Die zweite Studie untersuchte die Auswirkungen der Ko-Inokulation von Fos und einer PGPR (B. subtilis Isolat GB03) in einem parasitären S. hermonthica-Sorghum-System. Ungeachtet der Kolokalisierung von Fos und GB03 in gemeinsamen ökologischen Nischen des erkrankten S. hermonthica-Sprosses (hauptsächlich in flavonoidreichen Regionen) vereitelte GB03 die suppressive Aktivität von Fos gegen S. hermonthica. Interessanterweise wurde ein neuer, alternativer Fos-Eintrittsweg in S. hermonthica (durch das Trichom) entdeckt. Die Ko-Inokulation von Fos und GB03 brachte keinen zusätzlichen Vorteil bei der Bekämpfung von S. hermonthica. In der dritten Forschungsarbeit schließlich wurde eine Reihe hochgradig phytotoxischer Exometaboliten von Fusarium gegen die Keimung von S. hermonthica-Samen (in vitro) und das Auftreten (in planta) untersucht. Damit sollte der wirksamste/effizienteste Exometabolit von Fusarium für die Biokontrolle von S. hermonthica ermittelt werden. Unter den getesteten Exometaboliten war Diacetoxyscirpenol (DAS) der wirksamste, um S. hermonthica sowohl in vitro als auch in planta vollständig zu unterdrücken. Fos produzierte jedoch kein DAS, was auf die Unterexpression von Schlüsselgenen zurückzuführen ist, die für die Biosynthese von Fusarium-Trichothecen notwendig sind. Zusammenfassend lässt sich sagen, dass aufgrund des obligaten Auskreuzungssystems in S. hermonthica genomische Variation ein unvermeidliches Phänomen ist. Dies spielt daher eine entscheidende Rolle bei der variablen Anfälligkeit von S. hermonthica gegenüber Fos. Der neu entdeckte (direkte) Eintrittsweg von Fos in S. hermonthica (Trichom-Eintritt) stellt ein neues Paradigma für den Infektionsmechanismus dar, der im Rahmen der Interaktion zwischen S. hermonthica (Wirt) und Fos (Erreger) abläuft, zusätzlich zu der zuvor berichteten indirekten Rhizosphären-Übertragung. Diese neuartige Phyllosphären-Übertragung ebnet somit den Weg für weitere Forschungen, die diesen alternativen Fos-Infektionsweg für eine bessere Biokontrolle von S. hermonthica nutzen. Schließlich könnte der Exometabolit DAS in Anbetracht seiner Potenz und breiten Wirksamkeit gegen verschiedene S. hermonthica-Populationen als neuer Wirkstoff für eine effizientere Biokontrolle von S. hermonthica dienen. Allerdings ist eine weitere Untersuchung seiner spezifischen Wirkungsweise gegen das Zielunkraut (S. hermonthica) im Gegensatz zu Nicht-Zielorganismen erforderlich

Understanding the diverse roles of soil organic matter in the cereal - Striga hermontica interaction

Keywords: Striga hermonthica, Sorghum bicolor, soil fertility, organic matter, N-mineralisation, farmers’ priority, production constraints, intensification. The problem of the parasitic weed striga (Striga hermonthica (Del.) Benth.) has worsened for African farmers, in conjunction with degrading soil fertility. An analysis of the striga problem showed that scientists, policy makers and farmers conceptualise striga differently. Whether striga is viewed as a weed or a symptom of degraded soils raises two questions: Should farmers control striga, even when the impact on yields would be negligible? Or should fertility enhancement, leading to higher yields, be their focus, even when not accompanied by an immediate reduction in striga? This study seeks to understand how organic matter inputs affect nutrient dynamics, sorghum (Sorghum bicolor [L.] Moench) production and striga abundance. Surveys in northern Cameroon showed that striga infestation increased over the past two decades. Increased land pressure led to reduced fallow periods and enhanced cereal (mono-) cropping. Reduced access to fertiliser and manure hampered options to improve soil fertility. Yields from farmers’ fields did not correlate with striga incidence, confirming farmers’ prioritisation of soil fertility, weeds, and labour as production constraints, rather than striga. The entry point to tackle low yields and the worsening of the striga situation should follow farmers’ priority of alleviating low soil fertility. Whether and how soil fertility improvement, through organic matter, enhances agricultural productivity and reduces striga, was investigated in field experiments. Organic matter amendments significantly depressed striga seed survival, with the strongest effect achieved at higher quality; presumably due to higher microbial activity. Organic matter enhanced soil water retention and soil temperature but without effects on striga seed survival. Organic matter did not affect soil ethylene concentrations. The effect of organic matter amendments was directly related to N mineralisation, both for better cereal growth and reduced striga survival. The organic matter amendments and use of fallow, as applied here, however, may not be practicable for the resource-poor farmer. Increasing N-fertilisation increased sorghum root N mass concentration, which resulted in a lower striga seed germination. That relationship was linear up to a root N mass concentration of 19.5 mg g-1 where seed germination was close to but always still above 0%. In a broader framework of the research findings, the ultimate solution for farm productivity for Africa is in sustainable farm intensification by investing in soil fertility. However, the prevailing land tenure system and limited access to fertiliser and organic matter need to be overcome. A new conceptual model is proposed, indicating how changes in both cereal yield and striga infestation over time co-vary with changes in soil fertility. The implication of this model is that recovery of soil fertility should be the priority. The challenge to agronomists remains to consider how to make farm intensification rewarding and attainable for resource-poor farmers. In areas where striga is an obstacle, an integrated scheme for the intensification of cereal cropping should start with integrated soil fertility management. Crop rotation and intercropping with selected non-host leguminous crops are essential ingredients. </p

Enhancing Smallholder Farmers' Access to Seed of Improved Legume Varieties Through Multi-stakeholder Platforms

This open access book shares the experiences of Tropical Legumes III (TLIII) project in facilitating access to seed of improved legume varieties to smallholder farmers through innovation platforms. It highlights practices and guiding principles implemented in eight developing countries of sub-Saharan Africa and South Asia. This book details key processes that respective teams employed to create an innovation space that delivers seed, other inputs, knowledge and financial services to agricultural communities and most importantly, the underserved farmers in remote areas of the drylands. It offers valuable insights into the pathway to establishing, promoting and operating innovation platforms to enhance the performance and competitiveness of legume crops’ value chains, and addresses critical issues that must be considered to make innovation platforms more sustainable and attractive to beneficiaries. The book offers a wealth of practical insights for development workers, technical staff, and project managers. This publication is all about TLIII community of practice. It will definitely inspire other development workers and scientists to share their own experiences for others to learn from

Enhancing Smallholder Farmers’ Access to Seed of Improved Legume Varieties Through Multi-Stakeholder Platforms

The high percentage of farmers (80–90%), including the pro-poor in remote areas, who have no access to recently released and high-yielding varieties proves the failure of various seed delivery models implemented so far. The ideal model to grow a crop commodity business to reach farmers in developing countries with seed of improved legume crop varieties has been a hard topic for development organizations. Past studies have shown that the full and balanced integration of multiple stakeholders’ knowledge and contexts into the process of agricultural technology development increases the uptake and ownership among end users