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Persistent viruses include members of the family Endornavirus that cause no apparent disease and are transmitted exclusively via seed or pollen. It is speculated that these RNA viruses may be mutualists that enhance plant resilience to biotic and abiotic stresses. Using reverse transcription coupled polymerase chain reactions, we investigated if common bean (Phaseolus vulgaris L.) varieties popular in east Africa were hosts for Phaseolus vulgaris endornavirus (PvEV) 1, 2 or 3. Out of 26 bean varieties examined, four were infected with PvEV1, three were infected with both PvEV1 and PvEV2 and three had infections of all three (PvEV) 1, 2 and 3. Notably, this was the first identification of PvEV3 in common bean from Africa. Using high throughput sequencing of two east African bean varieties (KK022 and KK072), we confirmed the presence of these viruses and generated their genomes. Intra- and inter-species sequence comparisons of these genomes with comparator sequences from GenBank revealed clear species demarcation. In addition, phylogenetic analyses based on sequences generated from the helicase domains showed that geographical distribution does not correlate to genetic relatedness or the occurrence of endornaviruses. These findings are an important first step toward future investigations to determine if these viruses engender positive effects in common bean, a vital crop in east Africa.

'Candidatus Liberibacter' species are associated with severe, economically important diseases. Nearly all known species are putatively insect-transmitted, specifically by psyllids. Detection of 'Ca. Liberibacter' in plants is complicated by their uneven distribution in host plants and largely fastidius nature. The death of black (Fraxinus nigra) and mancana (Fraxinus mandshurica) ash trees in Saskatchewan, Canada has been associated with infestation by the cottony ash psyllid (Psyllopsis discrepans). A combination of conventional polymerase chain reaction (PCR) amplification and Sanger sequencing of the 16S rDNA was used to detect and identify 'Ca. Liberibacter' in psyllids collected from ash trees in Saskatchewan. BLAST analysis of two 16S sequences that were 1058 and 1085 bp long (NTHA 5: GenBank accession number MK942379 and NTHA 6: GenBank accession number MK937570, respectively) revealed they were 99-100% similar to a 'Ca. Liberibacter solanacearum' sequence (GenBank accession number: KX197200) isolated from the Nearctic psyllid (Bactericera maculipennis) of United States (US) provenance. Sequencing the psyllid genes CO1 and Cyt-b confirmed that the psyllids from which the bacterial DNA was isolated were P. discrepans based on comparisons with sequences in GenBank and BOLD and a reference sample from the United Kingdom. These results provide the first evidence that 'Ca. Liberibacter solanacerum' species are associated with psyllids collected from ash trees and specifically P. discrepans. The recent episodes of dieback of ash in Saskatchewan associated with psyllid feeding are consistent with disease symptoms caused by 'Ca. Liberibacter' pathogens and this possibility warrants further study.

We investigated the susceptibility of five cabbage varieties (‘Oxylus’, ‘Super Cross’, ‘Vantar F1 Hybrid’, ‘Santa’F1 and ‘Fortune’) to aphids. Trials were set up in the Accra plains for two rainy seasons in 2017. The first trial examined aphids’ infestation and the second included weekly blanket spray of neem oil at 0.48 L/ha (60ml/15L water) during the second rainy season. Five systematically sampled cabbage leaves per plot were examined for the numbers of aphids and associated natural enemies (predators). Symptoms of aphid attack (incidence and severity of infestation) were also recorded. Lipaphis erysimi pseudobrassicae (Davis) and Myzus persicae (Sulzer) (Hemiptera: Aphididae) were the two aphid species observed and their numbers differed significantly between varieties in both seasons during the first but not the second trial. Few aphids settled on ‘Oxylus’, while more occurred on ‘Fortune’. L. e. pseudobrassicae was the most abundant aphid on all the varieties. Aphid numbers were significantly decreased by neem application. Occurrence of natural enemies did not differ significantly between varieties, except for spiders during the major rainy season. There was no significant difference in aphid infestation between varieties during the first season as all of them completely succumbed to the infestation, while in the second season aphid incidence and severity of infestation was highest on ‘Fortune’, with ‘Oxylus’ being the least attacked by aphids. The crop yield was zero during the first season without protection for all the varieties. However, in the second season, lower yields (0.19-3.66 t/ha) was obtained with cabbage without protection, and much higher yields (14.8-21.1 t/ha) were obtained on neem-treated plots.

Bean common mosaic virus (BCMV), bean common mosaic necrosis virus (BCMNV), and cucumber mosaic virus (CMV) are important pathogens of common bean (Phaseolus vulgaris), a crop vital for food security in sub-Saharan Africa. These viruses are vectored by aphids non-persistently, with virions bound loosely to stylet receptors. These viruses also manipulate aphid-mediated transmission by altering host properties. Virus-induced effects on host-aphid interactions were investigated using choice test (migration) assays, olfactometry, and analysis of insect-perceivable volatile organic compounds (VOCs) using gas chromatography (GC)-coupled mass spectrometry, and GC-coupled electroantennography. When allowed to choose freely between infected and uninfected plants, aphids of the legume specialist species Aphis fabae, and of the generalist species Myzus persicae, were repelled by plants infected with BCMV, BCMNV, or CMV. However, in olfactometer experiments with A. fabae, only the VOCs emitted by BCMNV-infected plants repelled aphids. Although BCMV, BCMNV, and CMV each induced distinctive changes in emission of aphid-perceivable volatiles, all three suppressed emission of an attractant sesquiterpene, α-copaene, suggesting these three different viruses promote migration of virus-bearing aphids in a similar fashion.

Candidatus Liberibacter species cause severe, economically important diseases. All known species of these pathogens are putatively insect-transmitted, specifically by psyllids. Detection of Liberibacter in plants is complicated by its uneven distribution in host plants and largely unculturable nature. The death of black (Fraxinus nigra) and mancana (Fraxinus mandshurica) ash trees in Saskatchewan, Canada has been associated with infestation with the cottony ash psyllid (Psyllopsis discrepans). We hypothesized that the symptoms and death could be due to a psyllid-transmitted Liberibacter. We used a combination of conventional PCR and Sanger sequencing of the 16S rDNA for detection of Liberibacter, and the genes CO1 and Cyt-b to determine species of psyllids. The 16S sequencing generated two sequences, NTHA 5 (GenBank accession number MK942379) and NTHA 6 (GenBank accession number MK937570) that were 1058 and 1085 bp long. A BLAST search for homology showed 99-100% sequence similarity to a Candidatus Liberibacter solanacearum sequence (GenBank accession number: KX197200) isolated from the Nearctic psyllid (Bactericera maculipennis) of US provenance. CO1 and Cyt-b gene sequencing of our psyllids yielded sequence information confirming that they were P. discrepans from comparisons with sequences in GenBank and BOLD. Confirmatory sequence comparison with a reference sample from the United Kingdom was concurrent. These results provide the first evidence on the likely cause of ash dieback in Saskatchewan. Further, they suggest a relatively rare example of a Liberibacter adapting a new host plant.

The presence of large colonies of aphids is associated with a devastating novel necrotic disease of cabbage (Brassica oleracea var. capitata) in Ghana that is thought to be of viral etiology. In this study, we used molecular taxonomic tools to identify the aphid species present on these diseased cabbage plants. This was confirmed using two key features for morphological identification, involving the length of cornicles and shape of cauda for the wingless forms of the aphids. Two species of aphids were identified and their distribution in Ghana indicated. One was the generalist aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) but the most abundant was the brassica specialist aphid, Lipaphis erysimi pseudobrassicae (Davis) (Hemiptera: Aphididae), which is one of the most destructive pests of brassica crops in some countries in Africa and other parts of the world. L. erysimi has been reported in Benin, Mali, South Africa, India, China, and United States, but this is the first formal report of L. erysimi pseudobrassicae in Ghana. The correct identification of L. erysimi is crucial, suggesting that it has recently become one of the most common species of aphid found on cabbage plants in Ghana.

Bean common mosaic virus (BCMV), bean common mosaic necrosis virus (BCMNV), and cucumber mosaic virus (CMV) cause serious epidemics in common bean (Phaseolus vulgaris), a vital food security crop in many low-to-medium income countries, particularly in Sub-Saharan Africa. Aphids transmit these viruses “non-persistently,” i.e., virions attach loosely to the insects' stylets. Viruses may manipulate aphid-host interactions to enhance transmission. We used direct observation and electrical penetration graph measurements to see if the three viruses induced similar or distinct changes in feeding behaviors of two aphid species, Aphis fabae and Myzus persicae. Both aphids vector BCMV, BCMNV, and CMV but A. fabae is a legume specialist (the dominant species in bean fields) while M. persicae is a generalist that feeds on and transmits viruses to diverse plant hosts. Aphids of both species commenced probing epidermal cells (behavior optimal for virus acquisition and inoculation) sooner on virus-infected plants than on mock-inoculated plants. Infection with CMV was especially disruptive of phloem feeding by the bean specialist aphid A. fabae. A. fabae also experienced mechanical stylet difficulty when feeding on virus-infected plants, and this was also exacerbated for M. persicae. Overall, feeding on virus-infected host plants by specialist and generalist aphids was affected in different ways but all three viruses induced similar effects on each aphid type. Specifically, non-specialist (M. persicae) aphids encountered increased stylet difficulties on plants infected with BCMV, BCMNV, or CMV, whereas specialist aphids (A. fabae) showed decreased phloem ingestion on infected plants. Probing and stylet pathway activity (which facilitate virus transmission) were not decreased by any of the viruses for either of the aphid species, except in the case of A. fabae on CMV-infected bean, where these activities were increased. Overall, these virus-induced changes in host-aphid interactions are likely to enhance non-persistent virus transmission, and data from this work will be useful in epidemiological modeling of non-persistent vectoring of viruses by aphids.

Engineering plants for resistance to virus transmission by invertebrate vectors has lagged behind other forms of plant protection. Vectors typically transmit more than one virus. Thus, vector resistance could provide a wider range of protection than defenses directed solely against one virus or virus group. We discuss current knowledge of vector-host-virus interactions, the roles of viral gene products in host and vector manipulation, and the effects of semiochemicals on host-vector interactions, and how this knowledge could be employed to disrupt transmission dynamics. We also discuss how resistance to vectors could be generated through genetic engineering or gene editing or indirectly through use of biocontrol using plant-resident viruses that infect vectors.

Highlights • Non-persistent transmission is the most common mode for aphid-mediated virus transmission. • Many non-persistently transmitted viruses indirectly modify aphid behavior in ways that may enhance transmission. • Mathematical modeling confirms that enhancing host attractiveness while deterring aphid settling enhances local transmission. • Modeling predicts that encouraging settling promotes winged aphid production, which may enhance long distance transmission. • Disrupting host-vector interactions may provide a sustainable means to protect crops., Aphids vector many plant viruses in a non-persistent manner i.e., virus particles bind loosely to the insect mouthparts (stylet). This means that acquisition of virus particles from infected plants, and inoculation of uninfected plants by viruliferous aphids, are rapid processes that require only brief probes of the plant’s epidermal cells. Virus infection alters plant biochemistry, which causes changes in emission of volatile organic compounds and altered accumulation of nutrients and defence compounds in host tissues. These virus-induced biochemical changes can influence the migration, settling and feeding behaviours of aphids. Working mainly with cucumber mosaic virus and several potyviruses, a number of research groups have noted that in some plants, virus infection engenders resistance to aphid settling (sometimes accompanied by emission of deceptively attractive volatiles, that can lead to exploratory penetration by aphids without settling). However, in certain other hosts, virus infection renders plants more susceptible to aphid colonisation. It has been suggested that induction of resistance to aphid settling encourages transmission of non-persistently transmitted viruses, while induction of susceptibility to settling retards transmission. However, recent mathematical modelling indicates that both virus-induced effects contribute to epidemic development at different scales. We have also investigated at the molecular level the processes leading to induction, by cucumber mosaic virus, of feeding deterrence versus susceptibility to aphid infestation. Both processes involve complex interactions between specific viral proteins and host factors, resulting in manipulation or suppression of the plant’s immune networks.

The closely related potyviruses Bean common mosaic virus (BCMV) and Bean common mosaic necrosis virus (BCMNV) are major constraints on common bean (Phaseolus vulgaris) production. Crop losses caused by BCMV and BCMNV impact severely not only on commercial scale cultivation of this high-value crop but also on production by smallholder farmers in the developing world, where bean serves as a key source of dietary protein and mineral nutrition. In many parts of the world, progress has been made in combating BCMV through breeding bean varieties possessing the I gene, a dominant gene conferring resistance to most BCMV strains. However, in Africa, and in particular in Central and East Africa, BCMNV is endemic and this presents a serious problem for deployment of the I gene because this virus triggers systemic necrosis (black root disease) in plants possessing this resistance gene. Information on these two important viruses is scattered throughout the literature from 1917 onward, and although reviews on resistance to BCMV and BCMNV exist, there is currently no comprehensive review on the biology and taxonomy of BCMV and BCMNV. In this chapter, we discuss the current state of our knowledge of these two potyviruses including fundamental aspects of classification and phylogeny, molecular biology, host interactions, transmission through seed and by aphid vectors, geographic distribution, as well as current and future prospects for the control of these important viruses.

The closely related potyviruses Bean common mosaic virus (BCMV) and Bean common mosaic necrosis virus (BCMNV) are major constraints on common bean (Phaseolus vulgaris) production. Crop losses caused by BCMV and BCMNV impact severely not only on commercial scale cultivation of this high-value crop but also on production by smallholder farmers in the developing world, where bean serves as a key source of dietary protein and mineral nutrition. In many parts of the world, progress has been made in combating BCMV through breeding bean varieties possessing the I gene, a dominant gene conferring resistance to most BCMV strains. However, in Africa, and in particular in Central and East Africa, BCMNV is endemic and this presents a serious problem for deployment of the I gene because this virus triggers systemic necrosis (black root disease) in plants possessing this resistance gene. Information on these two important viruses is scattered throughout the literature from 1917 onward, and although reviews on resistance to BCMV and BCMNV exist, there is currently no comprehensive review on the biology and taxonomy of BCMV and BCMNV. In this chapter, we discuss the current state of our knowledge of these two potyviruses including fundamental aspects of classification and phylogeny, molecular biology, host interactions, transmission through seed and by aphid vectors, geographic distribution, as well as current and future prospects for the control of these important viruses.

Cameroon has a wide range of agro-ecological zones, having indigenous chicken populations which are thought to be adapted and diversified. Genetic diversity of the Cameroon chicken populations from agro-ecological zones I, II, III and IV was assessed using 25 microsatellite markers. A total of 314 chickens were genotyped, revealing 226 distinct alleles and 24 private alleles (10.62%). The mean polymorphic information content was 0.57. The average observed, expected and unbiased frequencies of heterozygote were 0.60, 0.62 and 0.65 respectively, with the mean Shannon index of 1.21. The global inbreeding coefficient among population was 0.13. Inbreeding coefficient varied significantly with 4.27% variation observed among ecotypes. Within ecotypes the highest diversity was observed in the Bafang-Bakou population having 7.92±4.22 alleles per locus, 168.80±4.73 gene copies, 9 private alleles and 0.68±0.02 expected heterozigosity. However the same region displayed the highest inbreeding coefficient (0.13). In all the populations, 67% of the loci did not deviate significantly from the Hardy-Weinberg. The neighbor-joining tree, UPGMA cladogram as well as the Evanno’s population structure parameters revealed existence of 3 clusters in Cameroon chicken populations. The current study confirmed usefulness of microsatellites for studying genetic variation of the Cameroonian indigenous chicken. They demonstrate information on genetic variability of Cameroon local chicken populations, offer steps towards rational decision making prior to genetic improvement and conservation programs, without compromising the existence of each unique genotype.