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The A-strain of Maize streak virus (MSV) causes maize streak disease (MSD) which is a major biotic threat to maize production in sub-Saharan Africa. Previous studies have described different MSV strains of economic importance from southern and eastern African countries, and how eastern African regions are hubs for MSV diversification. Despite these efforts, and lack of extensive sampling, there is limited knowledge about the MSV-A diversity in Ethiopia. Here, field sampling of maize plants and wild grasses with visible MSD symptoms were carried out in western Ethiopian regions of Gambela, Oromia, and Benishangul-Gumuz, during the maize growing season of 2019. The complete genomes of MSV isolates (n = 60) were cloned and Sanger sequenced. We use a model based phylogenetic approach to analyse 725 full MSV genome sequences available in the GenBank together with newly recovered genomes from Ethiopia to determine their subtypes and recombinant lineages. Of the 127 fields accessed, MSD prevalence was highest at 96% in Gambela region, and lowest in Oromia at 66%. Highest mean symptom severity of 4/5, (where 5 is the highest and 1 the lowest) was observed for both Gambela and Benishangul-Gumuz. Our results show that these newly determined MSV isolates belong in the recombinant lineage V of the A1 subtype with the widest dissemination, and economic significance in the sub-Saharan Africa and the adjacent Indian Ocean islands.

Maize streak caused by the Maize streak virus (MSV, genus Mastrevirus) is transmitted by Cicadulina spp., and is responsible for considerable maize yield losses in all maize production zones in Africa, including Cameroon. A survey was conducted in 3 agro-ecological zones (AEZ) of Cameroon (Sudano-Sahelian: zone I, Western Highlands: zone III and Bimodal Rainforest: zone V) between November 2017 and November 2019 to determine the status of streak disease in maize farms. The incidence and severity were determined in 90 maize fields, 30 fields per AEZ; the effect of lightning on the disease was also assessed using 15 fields under shade and 15 opened fields per AEZ. The highest streak disease incidence (60%) was found in AEZ I, whereas the lowest incidence was 10% in AEZV. The highest disease incidence and severity (80% and 4.5 respectively) were observed in maize fields under shade as compared to open fields (70% and 4.5 respectively). The phylogenetic analysis of MSV sequences from symptomatic plants indicated it as MSV-A strain identical to be previously reported to determine the virus diversity in relation to the other characterization isolates. This information is important for the development of control strategies to limit yield losses due to MSV.

In this paper we formulated and analyzed an optimal deterministic eco-epidemiological model for the dynamics of maize streak virus (MSV) and examine the best strategy to fight maize population from maize streak disease (MSD). The optimal control model is developed with three control interventions, namely prevention (u1), quarantine (u2) and chemical control (u3). To achieve an optimal control strategy, we used the Pontryagin’s maximum principle obtain the Hamiltonian, the adjoint variables, the characterization of the controls and the optimality system. Numerical simulations are performed using Forward-backward sweep iterative method. The findings show that each integrated strategy is able to mitigate the disease in the specified time. However due to limited resources, it is important to find a cost-effective strategy. Using Incremental Cost-Effectiveness Ratio(ICER) a cost-effectiveness analysis is investigated and determined that the combination of prevention and quarantine is the best cost-effective strategy from the other integrated strategies. Therefore, policymakers and stakeholders should apply the integrated intervention to stop the spread of MSV in the maize population.

Rice is an important staple food in Nigeria, affected by several diseases especially viruses. This study was carried out to evaluate the incidence and severity of two important viruses on rice plants and to identify associated insects in the Federal Capital Territory (F.C.T), Abuja in 2019. Field experiment was carried out from June to October, 2019 at the Teaching and Research Farm of the Faculty of Agriculture, University of Abuja, Nigeria, where ten rice varieties were assessed for incidence and severity. The seed and leaf samples were collected for serological indexing. Data collected was subjected to statistical analysis using SPSS and mean separation was done with Duncan Multiple Range Test. Of the 210 leaf samples collected, FARO 61 and 44 had the lowest incidence (19%), while FARO 65 recorded the highest (25.3%). FARO 52 recorded the highest severity (46%) while FARO 61 and FARO 60 had the lowest severity (30.1%) for rice yellow mottle sobemo-virus (RYMV) and maize streak geminivirus (MSV). Insects such as Spittle bug (Locris rubens and Poophilus costalis), Ladybird beetle (Cheilomenes sulphurea) and Groundhopper (Paratettix sp) were trapped on the field. All rice seed and leaf samples collected did not test positive to RYMV and MSV using Enzyme-Linked immunosorbent assay (ELISA). This study provides the first research work on rice viruses in the FCT and further studies are recommended. Key words: Nigeria, rice, rice yellow mottle sobemo-virus (RYMV), maize streak geminivirus (MSV), incidence, severity, virus symptoms, enzyme linked immuno sorbent assay (ELISA).

Maize lethal necrosis disease (MLND) is a devastating viral disease of maize caused by double infection with Maize chlorotic mottle virus (MCMV) and any one of the Potyviridae family members. Management of MLND requires effective resistance screening and surveillance tools. In this study, we report the use of small RNA (sRNA) profiling to detect MLND causal viruses and further the development of alternative detection markers for use in routine surveillance of the disease‐causing viruses. Small RNAs (sRNAs) originating from five viruses namely MCMV, Sugarcane mosaic virus (SCMV), Maize streak virus (MSV), Maize‐associated totivirus (MATV) and Maize yellow mosaic virus (MYMV) were assembled from infected maize samples collected from MLND hot spots in Kenya. The expression of the identified viral domains was further validated using quantitative real‐time PCR. New markers for the detection of some of the MLND causal viruses were also developed from the highly expressed domains and used to detect the MLND‐causative viruses in maize and alternative hosts. These findings further demonstrate the potential of using sRNAs especially from highly expressed viral motifs in the detection of MLND causal viruses. We report the validation of new sets of primers for use in detection of the most common MLND causal viruses MCMV and SCMV in East Africa.

Maize lethal necrosis (MLN) is emergent in East Africa, first reported in 2011 in Kenya, and is devastating to maize production in the region. MLN is caused by coinfection of maize with the emergent maize chlorotic mottle virus (MCMV) and any of several maize-infecting potyviruses endemic in East Africa and worldwide. Here, we examined the distribution of MCMV and sugarcane mosaic virus (SCMV), the major viruses contributing to MLN in Rwanda. These and other viruses in maize across Rwanda were further characterized by deep sequencing. When identified, MCMV had high titres and minimal sequence variability, whereas SCMV showed moderate titres and high sequence variability. Deep sequencing also identified maize streak virus and other maize-associated viruses, including a previously described polerovirus, maize yellow mosaic virus, and barley yellow dwarf virus, diverse maize-associated totiviruses, maize-associated pteridovirus, Zea mays chrysovirus 1, and a maize-associated betaflexivirus. Detection of each virus was confirmed in maize samples by reverse transcription polymerase chain reaction.

Maize streak virus (MSV) continues to be a major biotic constraint for maize production throughout Africa. Concerning the quantitative nature of inheritance of resistance to MSV disease (MSVD), we sought to identify new loci for MSV resistance in maize using F2:3 population. The mapping population was artificially inoculated with viruliferous leafhoppers under screenhouse and evaluated for MSVD resistance. Using 948 DArT markers, we identified 18 quantitative trait loci (QTLs) associated with different components of MSVD resistance accounting for 3.1–21.4% of the phenotypic variance, suggesting that a total of eleven genomic regions covering chromosomes 1, 2, 3, 4, 5 and 7 are probably required for MSVD resistance. Two new genomic regions on chromosome 4 revealed the occurrence of co-localized QTLs for different parameters associated with MSVD resistance. Moreover, the consistent appearance of QTL on chromosome 7 for MSVD resistance is illustrating the need for fine-mapping of this locus. In conclusion, these QTLs could provide additional source for breeders to develop MSV resistance.

In this paper, we proposed and analyzed an optimal control deterministic model for the dynamics of Maize Streak Virus pathogen interaction with a pest invasion on Maize plant to examine the best st...

In this paper, an ecoepidemiological deterministic model for the transmission dynamics of maize streak virus (MSV) disease in maize plant is proposed and analysed qualitatively using the stability theory of differential equations.The basic reproduction number with respect to the MSV free equilibrium is obtained using next generation matrix approach. The conditions for local and global asymptotic stability of MSV free and endemic equilibria are established. The model exhibits forward bifurcation and the sensitivity indices of various embedded parameters with respect to the MSV eradication or spreading are determined. Numerical simulation is performed and dispalyed graphically to justify the analytical results.

Maize streak virus (MSV) belongs to the Geminiviridae. Four forms of MSV coat protein (CP) assemblages were isolated from infected plants: geminate capsids, T = 1 icosahedral capsids, pentamers and decamers of CPs. Sequential exposure of geminate capsids to increasing pH, from 4.8 to 7.2 was used to monitor capsid disassembly. The capsids remain intact at pH4.8, disassemble to decamers and pentamers by pH6.4 and aggregate by pH7.2. Similarly, high salt and divalent cations cause disassembly. The disassembly process was reversed in low pH and low salt, but resulted in empty (no DNA) single and geminate capsid assemblies. This is likely due to disruption of CP-DNA interactions under acidic conditions and suggests a mechanism of capsid assembly in which the genome is packaged into preformed empty capsids. The pH assay developed in this study provides a method for characterizing the conditions that are the determinants of geminivirus assembly and disassembly.

In Ethiopia, maize is the staple food and one of the main sources of calories particularly in the major maize producing-regions of the country. Survey was conducted to determine the prevalence, incidence and severity of foliar maize diseases in North Gondar Zone. A total of 150 farmers’ fields were randomly sampled from five districts (Chilga, Gondar zuria, Takussa, Metema and Dembia) in North Gondar Zone of Amhara Region during cropping seasons of 2015 and 2016 years. Five quadrants were examined per farmers’ field for estimation of maize foliar disease incidence and severity infestation. This was done followed by pathogen isolation and disease identification laboratory procedures. Both of two years surveyed data were collected, analyzed and expressed using simple percentage. Results indicated that the dominant maize diseases were caused by Exserohilum turcicum, Puccinia sorghi and Cercospora zeae-maydis pathogen. Maize disease incidence of E. turcicum ranged from 50 to 80%, P. sorghi 19 to 62% whereas that of C. zeae-maydis reached 42% on foliar maize disease. In addition 3-19% of disease incidence of maize streak virus was recorded from seemingly healthy maize plants. Among four identified diseases Turcicum leaf blight (TLB), Common leaf rust (CLR) and Gray leaf spot (GLS) were recorded as major disease, while maize streak virus (MSV) was as minor disease. The present study provides an indication of the incidence and severity of foliar diseases of maize on which management strategies could be derived to improve the maize production in the surveyed areas. Key words: Disease, foliar, incidence, maize, prevalence, severity.

Wheat dwarf virus (WDV), an important cereal pathogen, is closely related to Maize streak virus (MSV), a model virus of the Mastrevirus genus. Based on its similarity to known MSV resistance strategies, a truncated part of the WDV replication-associated (RepA) gene (WDVRepA215) and the WDV RepA gene with a mutated retinoblastoma-related protein (RBR) interaction domain (WDVRepA215RBRmut) were cloned into the pIPKb002 expression vector and transformed into immature embryos of spring barley cv. Golden Promise plants through Agrobacterium-mediated transformation. A detailed study of T1-generation plants infected by leafhoppers (Psammotettix alienus) fed on infection sources of variable strength was performed over a 5-week period encompassing the initial stages of virus infection. A DNA WDV TaqMan qPCR assay normalized using the DNA puroindoline-b SYBR Green qPCR assay for samples on a per week basis revealed an approximately 2-week delay in WDVRepA215RBRmut plants to WDVRepA215 plants before significant increases in the WDV viral levels occurred. Both WDVRepA215 and WDVRepA215RBRmut plants showed similar levels of transgenic transcripts over the screened period; however, the transgenic plants also showed increased numbers of infected plants compared to the control plants.

Aluminium toxicity in acidic soils (Al) and the maize streak virus disease (MSV) cause significant losses in maize productivity. These constraints can occur simultaneously in sub-Saharan Africa but there are no maize hybrids that combine resistance for both stresses. Therefore, the objectives of the study were to determine combining ability, gene action and heterosis for MSV and Al tolerance in maize. Ninety-nine experimental hybrids were generated from a 10 × 10 factorial mating design. The experimental maize hybrids, and 21 commercial hybrids were evaluated for MSV resistance under artificial infestation in Zimbabwe, and for grain yield and agronomic performance across eight environments in South Africa and Zimbabwe. Ninety-seven experimental hybrids and five standard control hybrids were evaluated for Al tolerance in a laboratory in South Africa. There were significant (p

Maize streak virus disease (MSVD), caused by Maize streak virus (MSV; genus Mastrevirus), is one of the most severe and widespread viral diseases that adversely reduces maize yield and threatens food security in Africa. An effective control and management of MSVD requires robust and sensitive diagnostic tests capable of rapid detection of MSV. In this study, a loop-mediated isothermal amplification (LAMP) assay was designed for the specific detection of MSV. This test has shown to be highly specific and reproducible and able to detect MSV in as little as 10 fg/µl of purified genomic DNA obtained from a MSV-infected maize plant, a sensitivity 105 times higher to that obtained with polymerase chain reaction (PCR) in current general use. The high degree of sequence identity between Zambian and other African MSV isolates indicate that this LAMP assay can be used for detecting MSV in maize samples from any region in Africa. Furthermore, this assay can be adopted in minimally equipped laboratories and with potential use in plant clinic laboratories across Africa strengthening diagnostic capacity in countries dealing with MSD.

Accelerating crop improvement for increased yield and better adaptation to changing climatic conditions is an issue of increasing urgency in order to satisfy the ever-increasing global food demand. However, the major bottleneck is the absence of high-throughput plant phenotyping methods for rapid and cost-effective data-driven variety selection and release in plant breeding. Traditional phenotyping methods that rely on trained experts are slow, costly, labor-intensive, subjective, and often require destructive sampling. We explore ways to improve the efficiency of crop phenotyping through the use of unmanned aerial vehicle (UAV)-based multispectral remotely sensed data in maize (Zea mays L.) varietal response to maize streak virus (MSV) disease. Twenty-five maize varieties grown in a trial with three replications were evaluated under artificial MSV inoculation. Ground scoring for MSV infection was carried out at mid-vegetative, flowering, and mid-grain filling on a scale of 1 (resistant) to 9 (susceptible). UAV-derived spectral data were acquired at these three different phenological stages in multispectral bands corresponding to Green (0.53–0.57 μm), Red (0.64–0.68 μm), Rededge (0.73–0.74 μm), and Near-Infrared (0.77–0.81 μm). The imagery captured was stitched together in Pix4Dmapper, which generates two types of multispectral orthomosaics: the NoAlpha and the transparent mosaics for each band. The NoAlpha imagery was used as input into QGIS to extract reflectance data. Six vegetation indices were derived for each variety: normalized difference vegetation index (NDVI), green normalized difference vegetation index (GNDVI), Rededge NDVI (NDVIrededge), Simple Ratio (SR), green Chlorophyll Index (CIgreen), and Rededge Chlorophyll Index (CIrededge). The Random Forest (RF) classifier was used to evaluate UAV-derived spectral and VIs with and without variable optimization. Correlations between the UAV-derived data and manual MSV scores were significant (R = 0.74–0.84). Varieties were classified into resistant, moderately resistant, and susceptible with overall classification accuracies of 77.3% (Kappa = 0.64) with optimized and 68.2% (Kappa = 0.51) without optimized variables, representing an improvement of ~13.3% due to variable optimization. The RF model selected GNDVI, CIgreen, CIrededge, and the Red band as the most important variables for classification. Mid-vegetative was the most ideal phenological stage for accurate varietal phenotyping and discrimination using UAV-derived multispectral data with RF under artificial MSV inoculation. The results provide a rapid UAV-based remote sensing solution that offers a step-change towards data availability at high spatial (submeter) and temporal (daily/weekly) resolution in varietal analysis for quick and robust high-throughput plant phenotyping, important for timely and unbiased data-driven variety selection and release in plant breeding programs, especially as climate change accelerates.

Highlights • New stress-tolerant maize hybrids were tested in four East African countries. • They were evaluated by 2,0252025 farmers (55% women) at 27 sites in Kenya and Rwanda. • New hybrids had 18% higher yields than commercial checks under farmers’ conditions. • Their yields were similar to those of commercial checks under optimal conditions. • Farmers generally gave the highest scores to the hybrids with the highest yields., The development and deployment of high-yielding stress tolerant maize hybrids are important components of the efforts to increase maize productivity in eastern Africa. This study was conducted to: i) evaluate selected, stress-tolerant maize hybrids under farmers’ conditions; ii) identify farmers’ selection criteria in selecting maize hybrids; and iii) have farmers evaluate the new varieties according to those criteria. Two sets of trials, one with 12 early-to-intermediate maturing and the other with 13 intermediate-to-late maturing hybrids, improved for tolerance to multiple stresses common in farmers’ fields in eastern Africa (drought, northern corn leaf blight, gray leaf spot, common rust, maize streak virus), were evaluated on-farm under smallholder farmers’ conditions in a total of 42 and 40 environments (site-year-management combinations), respectively, across Kenya, Uganda, Tanzania and Rwanda in 2016 and 2017. Farmer-participatory variety evaluation was conducted at 27 sites in Kenya and Rwanda, with a total of 2025 participating farmers. Differential performance of the hybrids was observed under low-yielding (3 t ha−1) environments. The new stress-tolerant maize hybrids had a much better grain-yield performance than the best commercial checks under smallholder farmer growing environments but had a comparable grain-yield performance under optimal conditions. These hybrids also showed better grain-yield stability across the testing environments, providing an evidence for the success of the maize-breeding approach. In addition, the new stress- tolerant varieties outperformed the internal genetic checks, indicating genetic gain under farmers’ conditions. Farmers gave high importance to grain yield in both farmer-stated preferences (through scores) and farmer-revealed preferences of criteria (revealed by regressing the overall scores on the scores for the individual criteria). The top-yielding hybrids in both maturity groups also received the farmers’ highest overall scores. Farmers ranked yield, early maturity, cob size and number of cobs as the most important traits for variety preference. The criteria for the different hybrids did not differ between men and women farmers. Farmers gave priority to many different traits in addition to grain yield, but this may not be applicable across all maize-growing regions. Farmer-stated importance of the different criteria, however, were quite different from farmer- revealed importance. Further, there were significant differences between men and women in the revealed-importance of the criteria. We conclude that incorporating farmers’ selection criteria in the stage-gate advancement process of new hybrids by the breeders is useful under the changing maize-growing environments in sub-Saharan Africa, and recommended to increase the turnover of new maize hybrids.

Alfalfa leaf curl virus (ALCV) is the first geminivirus for which aphid transmission was reported. Transmission byAphis craccivorawas determined previously to be highly specific and circulative. Using various complementary techniques, the transmission journey of ALCV was monitored from its uptake from infected plant tissues up to the head of its vector. ALCV was shown to be restricted to phloem tissues using fluorescencein situhybridization (FISH) and electropenetrography (EPG) monitoring of virus acquisition. Furthermore, the virus is heterogeneously distributed in phloem tissues, as revealed by FISH and quantitative PCR of viral DNA acquired by EPG-monitored aphids. Despite the efficient ingestion of viral DNA, about 106viral DNA copies per insect in a 15 h feeding period on ALCV-infected plants, the individual maximum transmission rate was 12 %. Transmission success was related to a critical viral accumulation, around 1.6×107viral DNA copies per insect, a threshold that generally needed more than 48 h to be reached. Moreover, whereas the amount of acquired virus did not decrease over time in the whole aphid body, it declined in the haemolymph and heads. ALCV was not detected in progenies of viruliferous aphids and did not affect aphid fitness. Compared to geminiviruses transmitted by whiteflies or leafhoppers, or to luteoviruses transmitted by aphids, the transmission efficiency of ALCV byA. craccivorais low. This result is discussed in relation to the aphid vector of this geminivirus and the agroecological features of alfalfa, a hardy perennial host plant.

For pathogens infecting single host species evolutionary trade-offs have previously been demonstrated between pathogen-induced mortality rates and transmission rates. It remains unclear, however, how such trade-offs impact sub-lethal pathogen-inflicted damage, and whether these trade-offs even occur in broad host-range pathogens. Here, we examine changes over the past 110 years in symptoms induced in maize by the broad host-range pathogen, maize streak virus (MSV). Specifically, we use the quantified symptom intensities of cloned MSV isolates in differentially resistant maize genotypes to phylogenetically infer ancestral symptom intensities and check for phylogenetic signal associated with these symptom intensities. We show that whereas symptoms reflecting harm to the host have remained constant or decreased, there has been an increase in how extensively MSV colonizes the cells upon which transmission vectors feed. This demonstrates an evolutionary trade-off between amounts of pathogen-inflicted harm and how effectively viruses position themselves within plants to enable onward transmission., SCOPUS: ar.j, info:eu-repo/semantics/published

The type of gene action conferring combined resistance to maize streak virus (MSV) and maize stripe virus (MStV) was investigated in a Quality Protein Maize (QPM) population, ART/98/SW6-OB. Full-sib and half-sib progenies generated using North Carolina Design I mating scheme were evaluated in 2015 and 2016 in two locations endemic to the viral diseases in Nigeria. Serological study was also conducted on the progenies to validate the disease scores on the field. Significant mean square of genotypes was observed for MSV severity, MStV incidence and severity, plant height and days to flowering, while mean square of environment by females in males’ interaction was significant for grain yield and MSV incidence. Estimates of additive variances were larger than dominance variance for grain yield and MSV severity with moderate to high narrow-sense heritability estimates. This indicates that there is adequate genetic variability for improving grain yield and resistance to MSV in the maize population. The mean titre values of MSV and MStV for the progenies were significantly higher than the healthy control. MSV and MStV incidence were negatively correlated to days to 50% silking. Titre values were negatively correlated with grain yield but positively correlated with MSV and MStV incidence. Recurrent selection method that capitalizes on both additive and dominance variances would be effective in improving the population for grain yield and resistance to MSV and MStV diseases. Key words: Correlation, gene action, maize streak virus, maize stripe virus, resistance, North Carolina design.

Maize streak virus (MSV, genus Mastrevirus, family Geminiviridae), vectored by the leafhoppers (Cicadulina sp.), is the most economically important viral disease of maize endemic to Sub-Saharan Africa and its offshore islands. Yield losses due to MSV are mainly controlled through use of resistant varieties. ‘Recovery’ (ability of plants to reduce symptom severity), is one of the types of resistance being used to develop MSV resistant cultivars through breeding. This study was conducted to map Quantitative Trait Loci (QTLs) associated with recovery resistance to MSV in a mapping population comprising 250 S1 lines derived from a cross between two MSV resistant lines. The population was genotyped using single nucleotide polymorphism (SNP) markers at 269 loci. A genetic map of 11 linkage groups was constructed comprising 230 SNP markers. Four QTLs, two putative QTLs with significant effect on chromosome 3 and two other QTLs with reduced effect on chromosomes 7 and 9, were identified from the population. The two QTLs on chromosome 3 together accounted for 47 to 51% of the total phenotypic variance while the other two QTLs accounted for 28 to 32% of the total variation. These QTLs originated from the two parents of the mapping population had both additive and dominance effects but interaction among the four loci was not significant. Further validation of these QTLs associated with recovery resistance in other diverse populations will lead to the development of new genomic resources to enhance breeding for MSV resistant maize. Keywords: Mastrevirus, Maize breeding, Maize streak, Leafhoppers, QTL

Background Maize lethal necrosis is caused by a synergistic co-infection of Maize chlorotic mottle virus (MCMV) and a specific member of the Potyviridae, such as Sugarcane mosaic virus (SCMV), Wheat streak mosaic virus (WSMV) or Johnson grass mosaic virus (JGMV). Typical maize lethal necrosis symptoms include severe yellowing and leaf drying from the edges. In Kenya, we detected plants showing typical and atypical symptoms. Both groups of plants often tested negative for SCMV by ELISA. Methods We used next-generation sequencing to identify viruses associated to maize lethal necrosis in Kenya through a metagenomics analysis. Symptomatic and asymptomatic leaf samples were collected from maize and sorghum representing sixteen counties. Results Complete and partial genomes were assembled for MCMV, SCMV, Maize streak virus (MSV) and Maize yellow dwarf virus-RMV (MYDV-RMV). These four viruses (MCMV, SCMV, MSV and MYDV-RMV) were found together in 30 of 68 samples. A geographic analysis showed that these viruses are widely distributed in Kenya. Phylogenetic analyses of nucleotide sequences showed that MCMV, MYDV-RMV and MSV are similar to isolates from East Africa and other parts of the world. Single nucleotide polymorphism, nucleotide and polyprotein sequence alignments identified three genetically distinct groups of SCMV in Kenya. Variation mapped to sequences at the border of NIb and the coat protein. Partial genome sequences were obtained for other four potyviruses and one polerovirus. Conclusion Our results uncover the complexity of the maize lethal necrosis epidemic in Kenya. MCMV, SCMV, MSV and MYDV-RMV are widely distributed and infect both maize and sorghum. SCMV population in Kenya is diverse and consists of numerous strains that are genetically different to isolates from other parts of the world. Several potyviruses, and possibly poleroviruses, are also involved. Electronic supplementary material The online version of this article (10.1186/s12985-018-0999-2) contains supplementary material, which is available to authorized users.

Maize is an important cereal crop in sub-Saharan Africa but production is adversely affected by maize streak virus disease (MSVD). In Ghana, re-occurrence of the disease has been reported in several regions, therefore, necessitating the development of resistant hybrids as the most sustainable and economical option. The objectives of the study were to identify parents and hybrids that combine MSVD resistance with high yield and determine the influence of maternal effect on the inheritance of MSVD resistance. To achieve these, five parental inbred lines namely: TZEI-4, TZEI-7, TZEI-22, TZEI-31 and TZEI-157 were crossed in a full diallel mating design during the major season of 2015. The resulting F1 hybrids were evaluated under natural and artificial infestations during the minor and major seasons of 2015/2016 using 9 x 3 alpha-lattice design with three replications. General combining ability (GCA) and specific combining ability (SCA) mean squares were significant for MSVD severity mean score and only SCA for grain yield. Additive gene effect was preponderant for MSVD severity mean score, whereas grain yield was influenced by non-additive gene effect. Maternal effect had no significant contribution to the inheritance of MSVD resistance. GCA by environment and SCA by environment mean squares were significant for MSVD severity mean score. GCA effects revealed that inbreds TZEI-7 and TZEI-22 were resistant to MSVD. They could be good combiners for grain yield in addition to TZEI-31 and TZEI-157. Hybrids TZEI-4*TZEI-22 and TZEI-4*TZEI-31 showed resistance to MSVD as revealed by their SCA effects and heterotic values. TZEI-7*TZEI-157, TZEI-31*TZEI-157, TZEI-22*TZEI-157 and TZEI-4*TZEI-22 had positive and significant SCA effect, mid-parent heterosis and high parent heterosis for grain yield. Promising hybrids TZEI-4*TZEI-22, TZEI-22*TZEI-157, TZEI-7*TZEI-157 and TZEI-31*TZEI-157 identified in this study should be further tested in multi-locations across Ghana to determine their stability and adaptability. Key words: Maize streak virus disease, grain yield, resistance, full diallel, general combining ability, specific combining ability.

Genetic vulnerabilities (GV) of maize (Zeamays L.) have been experienced for a half century globally. Research on quantitative gene resistance (here called “co-survival tolerance”) against GV have been studied on Puccinia sorghi common rust, Exserohilum turicum northern corn leaf blight, Bipolaris maydis Southern corn leaf blight, maize streak virus, parasitic witchweed Striga species, Puccinia polysora tropical rust, Peronosclerspora sorghi downy mildew and Ustilago maydis smut. Among the above GE experiences, the most striking experience was parasitic witchweed Striga hermonthica, S. asiatica and S. aspera species in Africa. Without co-survival tolerance, Striga problems in Africa may not be solved in next few decades. The tolerance is controlled by quantitative gene. African origin parasite problems are causing damage of Africa’s food crops in 7 billion US dollars annually. Parasites and hosts must be live together and co-survive in nature. The author’s experiences of GV with maize in China have been two popular hybrids; Jeungdan 958 and Seunok 335. The former hybrid was covered over 10 million ha during the period of 2007-2013. Its genetic vulnerability due to too wide areas of cultivation of a single hybrid was occurred by corn borers and smut. While Seunok 335 and its sister hybrids now cover majority of maize cultivation of North Eastern (NE) region of China. Seunok 335 has severe root lodging problem under storm. The author observed the lodging in the north of Shenyang, Liaoning Province in 2008, followed in the NE provinces. In addition, it was attacked by E. turcicum in the western region of Jilin Province. Both USA and China have a quarter of the world maize cultivation, each 35 million ha and produce average yield of 10.5 and 6.5t/ha, respectively. To increase maize production for feed, food and industries as well as to reduce climate changes, China’s maize cultivation and breeding must be focused on diverse hybrid development and machine harvest. The later returns stalk and leave to soil. Copies of super hybrids e.g. Seunok 335 by other companies must be discouraged. Under climate changes, breeding stable hybrids with tolerance controlled by QTL must be encouraged. Tolerance breeding has clear advantage from GMO because it shall provide a buffering effect minimizing mutation of aggressive genes. Under the climate changes, the tolerance breeding confers buffering effects of host stability. The author has bred hybrids with tolerance against major biotic and abiotic stresses. Target traits are normal field, sticky, sweet maize, bio energy maize with genes of bm3 + high sugar + leafy, and black herb maize.

Plant viruses are major constraints to crop production worldwide, causing US$60 billion losses annually. This study assessed various agricultural sector stakeholders’ knowledge and perceptions of plant viruses in Zimbabwe. Data was collected from six provinces using surveys and participatory rural appraisal methodologies between December 2013 and October 2014. Maize streak virus, Tobacco mosaic virus, Cucumber mosaic virus, Tomato mosaic virus and Groundnut rosette virus were ranked as the country’s five most important plant viruses by agricultural technical staff. Most (72%) technical staff rated Maize streak virus as the most important plant virus in Zimbabwe. Over 30% of farmers were self-taught to identify diseases, while only 15.3% were trained by agricultural extension staff. Most (95.8%) technical staff trained people in disease identification through running short courses, use of demonstration plots and field days. The majority (41.9%) of farmers recommended the use of radio/TV/newspaper broadcasts to improve virus awareness. Only 23.7% of farmers and 41.6% of technical staff had heard about TSWV/tospoviruses. While most (97.2%) technical staff rated TSWV/tospoviruses as “fairly important” to “very important” plant pathogens, only 15.7% were able to correctly identify tospoviral vectors. The study showed that there is poor knowledge of plant viruses the stakeholders in the agricultural sector. There is need to train the technical staff in plant virology so that they can disseminate their knowledge to farmers for improved virus disease management. Key words: Awareness, disease identification, tospoviruses, training.

The significance of applying different rates of soil elements on host selection by a viral vector was studied in a confined habitat, to understand the mechanism of host selection by the leafhopper (CicadulinambilaNaudé), a vector of Maize Streak Virus Disease (MSV). Field collected leafhoppers were used in a screen house to assess insect settling preferences by evaluating insect behavior towards host plants, exposed to different rates of nitrogen and phosphorus fertilizers (0, 25, 50 and 75kg/ha.). Analysis of the two elements in the host plant tissues showed significant variation in levels of percent nitrogen (% N: p = 0.031) and phosphorus (% P: p = 0.001). Similarly, a significantly higher number of insects settled on plants treated with a higher rate of nitrogen (21%) and phosphorus (44%), compared to low rates of the same (9% and 28% respectively) (p = 0.019). Host choice by insects was significantly longer phosphorus treated hosts (four days) than nitrogen treated (three days). No significant differences were detected in the analysis of host plants for % neutral detergent fibers, acid detergent fibers, lignin and tannins. However, regression analysis revealed that neutral detergent fibers had significantly negative relationship with nitrogen fertilizer, while and phosphorus showed a negative relationship with lignin. This study showed that fertilizer amendments can critically affect host attack by leafhoppers with amplifications on viral disease transmission.

In sub Saharan Africa, past effort has registered success in developing high yielding and foliar disease resistant maize (Zea mays L.) varieties, which are deficient in pro-vitamin A. A new initiative is to develop maize varieties, tolerant to foliar diseases and rich in pro-vitamin A carotenoids. To achieve this, yellow conversions of white testers and other elite maize varieties have been developed by the International Center for Maize and Wheat Development (CIMMYT). Unlike the white lines, limited information on agronomic performance and disease resistance is available for yellow maize conversions. This study was conducted to evaluate the performance of white maize and their corresponding yellow maize conversions for yield and tolerance to Maize streak virus (MSV) disease; and determine the inheritance patterns of these traits. Fourty seven three-way hybrids generated in a Line by tester mating design (North Carolina 2), 12 inbred lines (used as male parents), 4 single crosses (used as female parents) and 3 commercials checks were screened for resistance to Maize streak virus (MSV) disease at the National Crop Resources Research Institute (NaCRRI) in Uganda. The same genotypes were evaluated in a 9x5 alpha lattice design in three locations of Uganda (National Crop Resources Research Institute (NACRRI), National Semi Arid Resources Research Institute (NaSARRI) and Bulambuli) for agronomic performance. Results confirmed tolerance to MSV in testers CML202, CML395, CML444, CML445 and CML312-SR (white). Genotypes performed significantly differently for yield, anthesis days, plant height, ear height, husk cover, grain texture, reaction to Gray leaf spot (GLS) (P0.05) in agronomic performance and tolerance to diseases. General combining ability (GCA) was more important than specific combining ability (SCA) for most traits, except for anthesis days, Turcicum leaf blight (TLB), GLS and yield. GCA effects for yield were not significant in both lines (male parents) and single cross testers (female parents) of white and yellow conversions. However, two unique cases were observed for diseases; yellow conversion of line CML444 significantly combined for susceptibility to TLB; while tester CML312/CML442 combined for resistance to GLS. Additionally, there was low heritably estimates for tolerance to MSV and yield. Generally, there was no significant difference between white and corresponding yellow maize conversion, implying that there is no significant loss in MSV resistance and yield performance while converting white into yellow maize.Key words: Combining ability, pro-vitamin A, Zea mays L.

Agroinoculation is a technique permitting the transmission of geminivirus genomes cloned in Agrobacterium tumefaciens into a wide variety of mono- and dicotyledonous host plants. Most geminiviruses are obligately transmitted by insect vector species under natural conditions; therefore, agroinoculation has greatly simplified the study of this group of viruses. In many cases, agroinoculation has replaced insect transmission, and has been used to compare virulence characteristics among viruses. Here we report on the discovery that, in agroinfectious Maize streak virus constructs, the orientation of cloned viral genomes relative to the Cauliflower mosaic virus 35S (CaMV35S) promoter of the binary cloning vector pBI121 can significantly affect agroinfectivity of the constructs. Rates at which plants became symptomatic were significantly higher when agroinoculating maize seedlings with constructs containing the CaMV35S promoter upstream of the viral replication-associated protein (Rep) gene than when the same viruses were cloned either in the opposite orientation or into a vector without a strong eukaryotic promoter sequence. Plants infected using the construct with Rep cloned downstream of the CaMV35S promoter also displayed more stunting and, in the early stages of the infection, more severe chlorotic streak symptoms.

Despite the development and deployment of maize streak-resistant (SR) germ plasm, virus-induced symptoms are still commonly observed on maize in Lagos, Nigeria. Therefore, surveys were conducted between April 2001 and February 2002 to determine the identity, prevalence, and incidence of maize viruses in 18 local government areas (LGAs) in and around Lagos by visual examination and serodiagnostic screening of symptomatic plants. All 112 fields surveyed during the dry season (September to December) and 18 fields surveyed during the late dry season (December to February) had plants infected by Maize streak virus (MSV), whereas 97.1% of the 170 fields surveyed during the wet season (April to August) had plants infected by MSV. Maize mottle/chlorotic stunt virus (MMCSV) was prevalent in 99.1, 88.9, and 67.4% of the fields surveyed during the dry, late dry, and wet seasons, respectively. The incidence of MSV was higher in 16 of the LGAs. The highest incidence of MSV was 18.9%, whereas that of MMCSV was 7.4%. Serodiagnostic screening of leaf samples showing virus-induced symptoms, using antigen-coated plate enzyme-linked immunosorbent assay, indicated that 1,192/1,475 (80.8%) and 949/1,210 (78.4%) of the samples were positive for MSV and MMCSV, respectively. Vector transmission and host range studies confirmed the identity of the viruses. The results confirm the presence of MSV and MMCSV in Lagos and suggest that the use of MSV-susceptible cultivars is still widespread. Methods of ensuring effective utilization of existing SR germ plasm and controlling maize viruses in general are discussed.

Maize streak is the most widespread and important disease of maize in sub-Saharan Africa. Maize streak virus (MSV)-resistant maize germ plasm is available in several countries, but little is known about the stability of its resistance to MSV strains that may differ from one region to another. We used four maize inbred lines (CML312, CML206, CML216, and MSR) known to differ widely for their resistance to MSV in Harare, and evaluated their resistance to 20 MSV isolates collected from the wild during 2 years at locations across Zimbabwe. Maize streak development and symptom severity were evaluated in replicated greenhouse experiments using artificial inoculation via viruliferous leafhoppers. All 20 MSV isolates induced maize streak symptoms on moderately and highly susceptible genotypes by about 1 week after inoculation (WAI). Differences among isolates for severity of early maize streak symptoms were ephemeral, and resistance was accurately differentiated by all isolates by 3 to 4 WAI. Differences in final maize streak symptom scores induced by the isolates were statistically significant, but differed only by a maximum of 7% in 1999 and 19% in 2000. Although genotype, isolate, and genotype by isolate effects for maize streak symptom scores were significant (P < 0.01), relative MSV resistance of the genotypes was consistently ranked by all 20 MSV isolates.

Prior to the introduction of highly resistant sugarcane varieties, Sugarcane streak virus (SSV) caused serious sugar yield losses in southern Africa. Recently, sugarcane plants with streak symptoms have been identified across South Africa. Unlike the characteristic fine stippling and streaking of SSV, the symptoms resembled the broader, elongated chlorotic lesions commonly observed in wild grasses infected with the related Maize streak virus (MSV). Importantly, these symptoms have been reported on a newly released South African sugarcane cultivar, N44 (resistant to SSV). Following a first report from southern KwaZulu-Natal, South Africa in February 2006, a survey in May 2007 identified numerous plants with identical symptoms in fields of cvs. N44, N27, and N36 across the entire South African sugarcane-growing region. Between 0.04 and 1.6% of the plants in infected fields had streak symptoms. Wild grass species with similar streaking symptoms were observed adjacent to one of these fields. Potted stalks collected from infected N44 plants germinated in a glasshouse exhibited streak symptoms within 10 days. Virus genomes were isolated and sequenced from a symptomatic N44 and Urochloa plantaginea plants collected from one of the surveyed fields (1). Phylogenetic analysis determined that while viruses from both plants closely resembled the South African maize-adapted MSV strain, MSV-A4 (>98.5% genome-wide sequence identity), they were only very distantly related to SSV (~65% identity; MSV-Sasri_S: EU152254; MSV-Sasri_G: EU152255). To our knowledge, this is the first confirmed report of maize-adapted MSV variants in sugarcane. In the 1980s, “MSV strains” were serologically identified in sugarcane plants exhibiting streak symptoms in Reunion and Mauritius, but these were not genetically characterized (2,3). There have been no subsequent reports on the impact of such MSV infections on sugarcane cultivation on these islands. Also, at least five MSV strains have now been described, only one of which, MSV-A, causes significant disease in maize and it is unknown which strain was responsible for sugarcane diseases on these islands in the 1980s (2,3). MSV-A infections could have serious implications for the South African sugar industry. Besides yield losses in infected plants due to stunting and reduced photosynthesis, the virus could be considerably more difficult to control than it is in maize because sugarcane is vegetatively propagated and individual plants remain within fields for years rather than months. Moreover, there is a large MSV-A reservoir in maize and other grasses everywhere sugarcane is grown in southern Africa. References: (1) B. E. Owor et al. J Virol. Methods 140:100, 2007. (2) M. S. Pinner and P. G. Markham. J. Gen. Virol. 71:1635, 1990. (3) M. S. Pinner et al. Plant Pathol. 37:74, 1998.

Cotton not only provides the world’s best natural spinnable fibre but also its seed is a rich source oil and protein, which is best for food and livestock feed. A biotic and biotic stresses always a serious threat to cotton production world widely. There is a demand of such cultivars which could oppose these stresses with wide genetic variability. Molecular breeding along with marker technology opened new ways in crop improvement. Genome mapping which is the identification of genomic regions linked with different traits; using construction of linkage map and quantitative trait loci (QTL) analysis can be used to identify resistant sources with the use of marker assistant selection (MAS). Improvements in control of many biotic diseases like verticillium (V) and Fusarium Wilt (FW), Reniform and Root-knot Nematodes had been made using molecular breeding. Cotton leaf curl disease (CLCuD) is the most distressing diseases of cotton in Pakistan, north-western areas of India and some parts of Africa which could be improved using these biotechnological tools. In many agricultural crops viral diseases like tomato yellow leaf curl virus (TYLCV), tomato mosaic virus (ToMV), tomato spotted wilt virus (TSWV), rice black-streaked virus (RBSV), Maize Streak Virus (MSV), Maize dwarf mosaic virus (MDMV), SCMV (Sugarcane mosaic virus), WSMV (Wheat streak mosaic virus), MCDV (Maize chlorotic dwarf virus), MMV (Maize mosaic virus), MFSV (Maize fine streak virus), Rice Stripe Virus (RSV), Rice yellow mottle virus (RYMV), rice black-streaked dwarf virus (RBSDV) and Barley Yellow Dwarf Virus (BYDV) had been studied using molecular markers. This Review study provides explanation of molecular markers involved in crop improvement especially for disease resistance in cotton and other field crop which could carry out to find out CLCuD resistant sources in upland cotton.

Maize streak virus (MSV) is responsible for streak disease of maize and poses a serious threat to maize production in sub-Saharan Africa. Polygenic resistance to MSV has become an essential requirement in modern maize cultivars to mitigate yield losses. Many single nucleotide polymorphism (SNP) markers linked to putative MSV resistance loci have been identified for use in forward breeding. This study aimed to validate, using the high-throughput kompetitive allele specific PCR (KASP) assay, the diagnostic ability of the three SNP markers linked to the loci for the Msv1 resistance trait in 151 early generations inbred lines with diverse genetic backgrounds, together with nine MSV-resistant elite lines and a susceptible check (cv. Pool-16). The phenotypic responses were determined by MSV inoculation using viruliferous leafhoppers (Cicadulina triangular) under screenhouse conditions. Based on an established MSV disease rating system, the maize lines were categorized into resistant, moderately resistant, susceptible, and highly susceptible. The three SNPs associated with MSV resistance were detected in 133 lines, which were categorized as resistant (54), moderately resistant (76), and susceptible (1). The 18 early generation lines without these SNPs were classified as moderately resistant (10), susceptible (5), and highly susceptible (3). This study confirms the strong association of SNPs with MSV resistance and their usefulness for forward breeding in maize while emphasizing the need to identify additional markers to screen lines for MSV resistance without any ambiguity.