Cassava mosaic disease (CMD) threatens cassava ( Manihot esculenta ) production in Africa. A total of 24 selected cultivars were screened against CMD using combined molecular and greenhouse grafting tools. Disease severity was recorded for 10 weeks after inoculation and the molecular markers associated with CMD2 were detected by PCR. CMD severity significantly differed ( P < 0.0001) among cultivars. Twelve cultivars were morphologically resistant and eight of these possessed CMD2 and four did not. These results suggest that there are several CMD-resistant cassava cultivars that could be recommended for on-farm production and for conservation and breeding programs.

Populations of Xanthomonas axonopodis pv. manihotis and X. axonopodis pv. vignicola, causal agents of cassava and cowpea bacterial blight, respectively, were quantified in insects. The pathogens were found in the faeces, the intestines, and on the legs and mandibles of Zonocerus variegatus. Additionally, X. axonopodis pv. manihotis was localized in the insect gut by immunofluorescence microscopy. Xanthomonas axonopodis pv. manihotis survived at least 1 week in the insect intestines and at least 5 weeks in faeces kept under controlled conditions, while survival in faeces exposed to sunlight was <2 weeks. Five percentage [e.g. 5.8 · 10 7 colony-forming units (CFU)/g faeces] of the fed population of X. axonopodis pv. manihotis in cassava leaves were recovered viable in the faeces after passage through the insect. The transmission of cassava bacterial blight by pathogen-contaminated insect faeces to intact, healthy cassava leaves was demonstrated for the first time. Xanthomonas axonopodis pv. vignicola was isolated from organs and faeces of the grasshopper Pyrgomorpha cognata, the Senegalese grasshopper (Oedaleus senegalensis), bee (Apis mellifera) and three Coleoptera (Ootheca mutabilis, Mylabris spp., Exochomus troberti) collected in bacterial blight-infected cowpea fields. Cowpea belonged to the diet of 19 grasshopper species collected in cowpea fields as demonstrated by residues in their faeces. Pathogencontaminated Z. variegatus initiated an epiphytic population of 8.9 · 10 4 CFU/g on healthy cowpea leaves. Spraying cassava and cowpea leaves with 10 2 and 10 4 CFU/ml of their respective pathogen was sufficient to evoke symptoms. A possible role of insects in the transmission of X. axonopodis pvs. vignicola and manihotis is discussed.www.blackwell-synergy.com J. Phytopathology 155, 159-169 (2007) Journal compilation Ó 2007 Blackwell Verlag, Berlin No claim to original US government works 160 Zandjanakou-Tachin et al.

BackgroundCassava is an important crop in Africa that is widely cultivated for its starchy tuberous root, which constitutes a major source of dietary carbohydrates. Cassava mosaic disease (CMD) is the most devastating disease affecting cassava in Africa and causes enormous losses in yield. In Benin, specifically, cultivars resistant to CMD are not commonly planted, and even when CMD is observed in fields, farmers do not implement control measures, presumably because they lack proper knowledge and training. Our study aimed to evaluate farmers’ knowledge of CMD to determine whether there is consistency between farmers’ criteria for selecting cassava cultivars and the currently CMD-recommended cassava varieties.MethodsWe conducted structured interviews with 369 farmers in 20% of townships in each of three agro-ecological zones in Benin between November 2015 and February 2016. Farmers were selected randomly in each household, and their fields were assessed for CMD incidence and severity.ResultsAll farmers surveyed, representing a broad demographic pool with regard to education level, age group, and years of experience in cassava production, successfully recognized CMD symptoms in photos, but most (98.60%) said they did not know the causes and vectors of the disease. Most farmers (93.51%) reported that they obtain planting material from neighboring fields or their own fields. In total, 52 unique cultivars were identified, of which 3 (5.76%) were preferred based on their yield and precocity and 3 (5.76%) were preferred based on taste or ability for transformation. The assessment of disease incidence and severity showed that the areas most affected by CMD were Comè Township (37.77% of fields affected) and agro-ecological zone VIII (26.33%).ConclusionFarmers already know how to recognize the symptoms of CMD and could implement control measures against it if they are trained by researchers. Across all surveyed areas, we identified six preferred cultivars based on the four most commonly stated preference criteria (precocity, yield, gari, and taste. Our results suggest that farmers will be more likely to use CMD-resistant cultivars and clean plant material if the plants meet their existing preference criteria. We suggest that CMD-resistant cultivars will be embraced only if the recommended cultivars are strategically aligned with the characteristics desirable to the cassava farmers in each region.

Ribosomal coding DNA was sequenced and compared in 95 isolates of Mycosphaerella spp. collected in Nigeria and single nucleotide polymorphism (SNP) was used to identify the species and to determine the genetic structure of the sampled geographical populations. Using reference GenBank accessions with intercontinental distributions as controls, and shared species-specific SNPs in these control accessions, 84 (88·4%) isolates that grouped into 14 SNP haplotypes were identified as M. fijiensis , while 11 (11·6%) isolates represented by seven SNP haplotypes were characterized as M. eumusae . None of the isolates were either M. musicola or M. musae . The presence of M. fijiensis and M. eumusae in the collection was further confirmed using previously published species-specific probes designed on actin and β -tubulin gene sequences. A pairwise comparison of the population genetic distances revealed significant genetic differentiation between most populations ( P < 0·001), with an average F ST of 0·126, and a population structure corresponding to the four sampled geographical zones. The intraspecific dissimilarity of M. eumusae was 4·6%, compared with 2% for M. fijiensis . Compared to all the GenBank reference accessions, three sequence variations were unique to some Nigerian M. fijiensis haplotypes. Twenty-one sequence haplotypes were identified, geographically mapped and registered in GenBank. The results indicate that M. musicola has been replaced by more frequently occurring M. fijiensis and M. eumusae , against which disease management and resistance breeding efforts should be directed in Nigeria.