Summary The parasitic weeds Striga asiatica and Striga hermonthica cause devastating yield losses to upland rice in Africa. Little is known about genetic variation in host resistance and tolerance across rice genotypes, in relation to virulence differences across Striga species and ecotypes.Diverse rice genotypes were phenotyped for the above traits in S. asiatica‐ (Tanzania) and S. hermonthica‐infested fields (Kenya and Uganda) and under controlled conditions.New rice genotypes with either ecotype‐specific or broad‐spectrum resistance were identified. Resistance identified in the field was confirmed under controlled conditions, providing evidence that resistance was largely genetically determined. Striga‐resistant genotypes contributed to yield security under Striga‐infested conditions, although grain yield was also determined by the genotype‐specific yield potential and tolerance. Tolerance, the physiological mechanism mitigating Striga effects on host growth and physiology, was unrelated to resistance, implying that any combination of high, medium or low levels of these traits can be found across rice genotypes. Striga virulence varies across species and ecotypes. The extent of Striga‐induced host damage results from the interaction between parasite virulence and genetically determined levels of host–plant resistance and tolerance. These novel findings support the need for predictive breeding strategies based on knowledge of host resistance and parasite virulence.

Striga asiatica and Rhamphicarpa fistulosa are important parasitic weeds of rain-fed rice, partly distributed in similar regions in sub-Saharan Africa (SSA). It is not evident whether their ecologies are mutually exclusive or partially overlapping. In Kyela, a rice-growing area in south Tanzania where both parasites are present, three transects of about 3 km each across the uplandlowland continuum were surveyed in June 2012 and 2013. A total of 36 fields were categorised according to their position on the upland-lowland continuum as High, Middle or Low and soil samples were taken. In each field, parasitic and non-parasitic weed species were identified in three quadrats. Additionally, in two pot experiments with four different moisture levels ranging from wilting point to saturation, influence of soil moisture on emergence and growth of parasites was investi-gated. Striga asiatica was observed in higher lying drier fields, while R. fistulosa was observed in the lower lying wetter fields. Furthermore, non-parasitic weed species that were exclusive to S. asiatica-infested fields are adapted to open well-drained soils, while species that were exclusive to R. fistulosa fields are typical for wet soils. The experiments confirmed that S. asiatica is favoured by free-draining soils and R. fistulosa by waterlogged soils. These results imply that changes in climate, specifically moisture regimes, will be crucial for future prevalence of these parasitic weeds. The nonoverlapping ecological range between their habitats suggests that their distribution and associated problems might remain separate. Thus, management strategies can be focused independently on either species.

Time requirements, weed control efficacy, and yield effects of three labor-saving weed technologies were tested against hand weeding during three seasons in 2012 and 2013. The technologies included two hand-operated mechanical weeders, the straight-spike and the twisted-spike floating weeder, and the PRE application of oxadiazon. The straight-spike floating weeder reduced weeding time by 32 to 49%, the twisted-spike floating weeder reduced weeding time by 32 to 56%, and the application of herbicide required 88 to 97% less time than hand weeding. Herbicide application provided the best weed control in two of the three seasons. No differences in weed control efficacy were observed between mechanical and hand weeding. Yield differences were only observed in season 3 with higher rice yields after PRE application of oxadiazon compared with other weed management treatments.

Traditional ecological knowledge is an integrated part of the African people and indeed the Rwandese for cultural purpose. Buhanga sacred forest is a relict forest of tremendous ecological importance to Rwandan society located in Musanze District. The aim of this study was to assess the traditional ecological knowledge and belief in the utilisation of some important plant species for the conservation of Buhanga sacred forest. Ecological information about ethnomedicinal and traditional practices were collected following structured questionnaire through interview involving eight traditional healers and three focus group discussions. Data were collected from the natural habitats, home gardens, farmlands and roadsides of Buhanga sacred forest. A total of 45 botanical taxa belonging to 28 families were reported to be used by the local community. Species such as Brillantaisia cicatricosa and Senna septemtrionalis were the popular species cited by traditional healers to treat human and animal diseases and ailments, respectively. The results of the study indicated that because of the cultural norms and values associated with the sacred forest, this has led to non-exploitation. The study presents key sites and plant species in which their use and belief can lead to their conservation. However, not only is it imperative to conserve traditional local knowledge for biocultural conservation motives but there is also need to train traditional healers on how to domesticate indigenous species as conservation measure because some species have become susceptible to extinction.Conservation implications: Highlighting indigenous species investigated in this research will provide a powerful tool for ensuring biodiversity conservation through community participation in a country of high population density in Africa. Some plant species that provided satisfactory Local Health Traditions among communities surrounding Buhanga can contribute as good material for further research in Rwanda.

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