Close-up of corn and leaf streak virus chlorotic banding symptoms on a mature corn leaf. Relation of maize belt virus disease and its vectors (Homoptera: Cicadelidae) to soil macronutrients and altitude in Kenya.
Introduction
Maize and its importance in Africa
Production constraints of maize in Africa
Major biotic constraints
Maize streak virus disease
- Maize streak virus biology
- Maize streak virus disease geographic distribution
- Maize streak virus disease symptoms
- Damage caused by maize streak virus disease
- Control of maize streak virus disease
- Cultural practices
- Chemical practices
- Use of maize streak virus disease-resistant maize genotypes
Chlorosis of the entire lamina can develop from chlorotic lines in highly susceptible varieties (Thottappilly et al., 1993; Bosque-Perez, 2000; . Fajemisin, 2003). Insecticidal control of foliar fungi generally requires repeated applications of insecticides to control migrating fungi (Magenya et al., 2008).
Downy mildew disease
- Downy mildew biology
- Geographic distribution of downy mildew disease
- Symptoms of downy mildew
- Damage caused by downy mildew disease
- Control methods of downy mildew disease
- Cultural control
- Chemical control
- Use of downy mildew-resistant maize genotypes
In Africa, outbreaks of diabetes have been reported from Uganda, Mozambique and the Democratic Republic of Congo (Ajala et al., 2003). Downy mildew is one of the most devastating diseases of maize in Nigeria and Mozambique (Pingali and Pandey, 2001; Ajala et al., 2003).
Breeding of disease resistance maize varieties
- Qualitative resistance
- Quantitative resistance
- Nature and mechanism of MSV disease resistance
- Nature and mechanism of downy mildew disease resistance
Quantitative resistance can occur at any level between a minimum and a maximum level (Parlevliet, 1995; Robinson, 2006; Wisser et al., 2006). The genetics of DM resistance have been shown to be complex and polygenic in nature, with additive effects mainly contributing to resistance (George et al., 2003).
Classical breeding
Stability of QTL across populations has been shown to be variable; however, this is not the case for the MSVD QTL (Pernet et al., 1999). It has been suggested that genetic engineering is best utilized when manipulating traits that depend on one or a few genes (Boopathi et al., 2011).
Marker-assisted selection in plant breeding
Marker-assisted breeding vs. conventional breeding
Conventional breeding methodology, on the other hand, relies on phenotypic evaluation, which does not always accurately reveal the basic genomic information of the plant (Dreher et al., 2000; Collard et al., 2005). Environmental effects and genotype x environment interactions can significantly obscure the presence or absence of specific alleles, making it difficult for breeders to identify plants with desired traits (Dreher et al., 2000).
Application of markers for screening for disease resistance
This provides information on the number of genes or regions to be transferred through breeding programs (Redinbaugh et al., 2004). A study was conducted by Asea et al. 2008) to assess the utility of molecular markers linked to consensus QTL controlling partial resistance systems to NCLB, GLS and MSV in maize.
Molecular genetic screening techniques
- Restriction fragment length polymorphism (RFLPs)
- Random amplified polymorphic DNA (RAPDs)
- Amplified fragment length polymorphisms (AFLPs)
- Simple sequence repeats (SSRs)
- Single nucleotide polymorphisms (SNPs)
Random amplified polymorphic DNA analysis was developed independently by two different laboratories (Welsch and McClelland, 1990; Williams et al., 1990). Amplified fragment length polymorphisms technology developed by Vos et al. (1995) overcame the limitation of reproducibility of RAPDs (Agarwal et al., 2008).
High resolution melt (HRM) analysis technology
High-resolution melting analysis can be performed in approximately two minutes, so analysis of PCR amplicons using this technique enables rapid cost-effective genotyping, especially with large sample numbers, making it efficient in clinical and epidemiological studies (Gudrun and Wittwer, 2004; Steer et al., 2008).
FTA TM technology
Features and benefits of using FTA TM cards
DNA stored on FTATM cards was successfully amplified by PCR, whereas DNA stored on non-FTA cards was not amplified (Mbogori et al., 2006; McClure et al., 2009). The use of FTATM cards can thus reduce costs, sampling time and sample storage space (Ndunguru et al., 2005).
Genetic diversity and its importance for breeding
Genetic analysis of maize belt virus isolates from Uganda reveals wide distribution of a recombinant variant. Genetic diversity of maize germplasm lines and implications for breeding maize virus resistant hybrids.
Introduction
The adoption of hybrids in maize production has led to increased yields around the world (Warburton et al., 2002). However, molecular markers can detect variation at the DNA sequence level (Diniz et al., 2005) and are genetic distances (GD).
Materials and methods
- Plant material
- DNA extraction
- Simple sequence repeats primer selection
- PCR amplification and detection conditions
- Data analysis
PowerMarker v3.25 (Liu and Muse, 2005) was used to determine PIC, gene diversity, and heterozygosity values for each SSR marker used in the study. The allele frequency data from PowerMarker v3.25 were used to export the data in binary format for analysis with NTSYS-PC (Numerical Taxonomy and Multivariate Analysis for Personal Computers) v2.1.
Results
Genetic diversity
Observed heterozygosity was calculated by dividing the number of heterozygous individuals by the number of individuals scored. A dendrogram was constructed using the UPGMA (unweighted paired group method using arithmetic means) method as implemented in NTSYS-PC v2.1 to infer genetic relationships and phylogeny.
Analysis of maize genotype associations
The LP23 line was in a different cluster from the CML505 and CML509 lines, reflecting the large genetic distances between the lines. 68 Figure 2.1: UPGMA dendrogram of 25 maize inbred lines based on dice coefficient calculated using 19 SSR markers.
Discussion
Analysis of genetic diversity using simple sequence repeats
The CML505 and CML509 lines were derived from the same population with tropical lowland adaptation and powdery mildew resistance. Consistent with pedigree information, lines E46 and E47 were placed in the same cluster 2 because both lines were derived from ZM521.
Implications for breeding new hybrids
Implications for developing new inbred lines
Conclusions
Quantitative resistance loci to maize stripe virus disease in maize genotypes used in hybrid development. Maize stripe virus resistance gene in the African maize inbred line CIMMYT CML202.
Introduction
This was made possible by the ability of HRM to simultaneously detect and genotype DNA polymorphisms (Montgomery et al., 2007). High-resolution fusion assay, which requires less time compared to electrophoresis assay (Steer et al., 2008), was used for the analysis of microsatellite markers after PCR.
Materials and methods
- Germplasm and generations
- Tissue sampling and DNA collection
- Comparison of DNA extracted from FTA TM elute cards with
- DNA samples
- Simple sequence repeats (SSR) analysis
- PCR and HRM conditions
However, hybrid vigor in these lines is compromised by the susceptibility of the LP23 line to the MSV disease. Some of these markers were included in the screening of the possible parental lines but most were taken from Danson et al.
Results
Comparison of DNA extraction by FTA TM cards and that extracted
The primers were optimized in terms of the number of FTATM disks per elute to be used for each PCR reaction and the range of melting temperatures in the HRM assay. The fusion profile generated for each amplicon after real-time PCR was analyzed using Rotor-Gene 6000 Series Software (Version 1.7.87) (Corbett Research, Sydney, Australia).
Comparison of HRM melt profiles generated when sufficient and
PCR amplifications were performed in 20 µl reaction volumes consisting of approximately 20 ng genomic DNA template, 10 µl 2 x Quantace SensiMix for PCR reaction components, and 200 n m forward and reverse primers. 89 Figure 3.2: Melting profiles of genomic DNA extracted from FTATM elution cards with sufficient and insufficient plant juice printed on FTATM cards from parental line CML509 amplified using SSR primer umc2228.
HRM curve profiles for the screening for MSV resistance
91 Figure 3.4: Difference graph of the parental LP23 line and CML505/LP23 progeny lines in relation to the parental line CML505 (baseline). MSV- SUS MSV- RES msv-sus msv-sus msv-sus has msv-sus msv-sus msv-sus has msv-sus msv-sus has msv-sus msv-res msv-res msv-res msv-res msv- res msv-res msv-res msv-res msv-res msv-res msv-res msv-res msv-res msv-res msv-res msv-res.
Discussion
The polymorphism detected between the parental lines allowed the classification of the progeny genotypes. Such variation allows for improved discrimination and genotyping of the HRM curve analysis technique (Steer et al., 2008).
Conclusions
Classification of poultry adenovirus serotypes using high-resolution melting curve analysis of the hexon gene region. A screening method for detecting Simple Sequence Repeat (SSR) polymorphism of Zea Mays using high-resolution melting curve analysis.
Introduction
Combining multiple different resistance genes into a single genotype (gene pyramid) expands the expression of resistance in a new cultivar for sustainable permanent control of biotic stress in crops (Eibach et al., 2007; Joshi and Nayak, 2010). However, large areas are still planted with varieties that are not resistant to important pathogens (Paliwal, 2000; . Pratt et al., 2003).
Materials and methods
- Locations
- Germplasm and generations
- Establishment of screening nurseries and artificial inoculation for
- Planting
- Inoculation
- Disease assessment
- Establishment of screening nurseries and artificial inoculation of
- lnoculation
- Planting
- Disease assessment
- Statistical analysis
Seed inoculation from the local land variety was done by placing a layer of seedlings on top of the diseased leaf layer in clean containers and allowed to sporulate overnight in a 21oC incubator (Fig. 4.2D). Infected seedlings were planted in black clay soil at both ends of the field as propagating rows with 0.5 m inter-row spacing (Fig. 4.2E).
Results
Disease expression and effect of MSV disease on growth of parents
Visual assessments of DM disease severity were made on whole plots and the mean disease score of each progeny line was determined. Data for MSV disease scores and plant height for all plants and the parental lines LP23, CML505 and CML509 were analyzed by one-way analysis of variance (ANOVA) followed by the Newman-Keuls multiple comparison test to detect significant differences between lines. .
Disease expression and effect of MSV on growth of the progeny
Although there were no significant differences in MSV scores between CML505 and CML509, the latter had a significantly higher plant height than the former, which is attributed to genotypic differences.
Disease expression of DM in the progeny lines
Individual plants from a total of 41 progeny lines that exhibited MSV disease severity scores of 2.5 or less at both sites within each of the F3 family lines were then selected based on the presence of the msv1 gene as detected using SSR data (Chapter three ) or DM disease resistance in the field, ie for example NM-4 and NM-5 although detected in the marker, were chosen due to the limits of dominance of DM resistance. 122 Table 4.3: Dates of pollen shedding and silking, number of ears and MSV and DM results of 41 progeny lines.
Discussion
In the current study, the MSV disease severity score results recorded in Chokwe were not used to conduct evaluations. Recombination explains the lack of correlation between the marker and field data in the current study.
Conclusions
Significance and transmission of maize streak virus disease in Africa and options for management: an overview. However, productivity is affected by susceptibility to corn streak virus (MSV) disease.
Introduction
Several techniques have been developed to test for SNPs, including the Sequenom MassARRAY iPLEX genotyping platform (Gabriel et al., 2009). In this study, SNP genotyping was performed using the Sequenom MassArray genotyping platform (Sequenom, San Diego, USA), following standard protocols provided by Gabriel et al.
Materials and methods
- Plant material
- DNA Extraction
- SNP selection and amplification
- Statistical analysis
DNA extraction was performed using a Sarkosyl-based method (Hasan et al., 2008) at the DNA LandMarks laboratory in Quebec, Canada. SNP data were scored based on the presence or absence of marker alleles and these data were used to estimate genetic similarity (GS) between any pair of lines based on the Jaccard coefficient using the NTSYSpc v2.1 software package (Exeter Software Setauket, NY, USA ). A dendrogram showing the genetic relatedness between lines was constructed by the unweighted pairwise group method using the method of arithmetic means (UPGMA).
Results
Genetic diversity levels
Greater genetic distances were observed between all DMSR progeny lines and the MSV-resistant CML505 donor parent, with lineage similarity to CML505 ranging from 60% to 83%. It is clearly shown that the progeny lines were more distantly related to CML509 than to the other parental lines.
Patterns of genetic diversity
Discussion
However, there were high levels of variation between the control lines, with the lines in Groups 1 to 5 consisting of temperate lines B73, MO17 and South African lines (DXL37 and 8CED67; H24W), which are derived from temperate and subtropical material. The genetic distances between the lines varied from 12% to 48% (Table 5.3) and this can be explained by the fact that only 400 SNPs were used in the present study.
Conclusions
Microsatellite analysis of the correlation between molecular and morphological traits in different maize inbred lines. Selection of suitable lines for the introgression of the msv1 gene for improved heterosis in a cultivar for Mozambique.
Similarity matrix of the 50 maize inbred lines based on 400 SNP
![Table 3.2: List of potential 10 SSR markers for msv1 introgression (Chr 1.04-0.5) [Danson et al., 2006; Maize database (www.maizegdb.org)]](https://thumb-ap.123doks.com/thumbv2/pubpdfnet/10640687.0/103.892.108.817.670.1035/table-potential-markers-introgression-danson-maize-database-maizegdb.webp)
