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  • 1
    Electronic Resource
    Electronic Resource
    QTL for Resistance to Setosphaeria turcica in Tropical African Maize (1999)
    Springer
    Crop science 39 (1999), S. 514-523 
    Details
    ISSN: 1435-0653
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Setosphaeria turcica (Luttrell) Leonard & Suggs causes northern corn leaf blight (NCLB), an important disease of maize (Zea mays L.) in sub-Saharan Africa and other tropical and temperate regions. Quantitative trait loci (QTL) for resistance were mapped and characterized in a population of F2∝3 lines derived from a cross between the susceptible line Lo951 and the highly resistant CIMMYT line CML202, and tested in three inoculated trials in Kenya (n = 194-256 lines). Incubation period (IP) and area under the disease progress curve (AUDPC, based on three readings) were assessed. Both traits showed a continuous distribution in the population with no transgressive segregation. Variance components for genotypes (G) and environments (E) were highly significant for both traits. G × D interaction was also significant but less important. Heritability was 0.86 for IP and 0.81 for AUDPC. Genotypic and phenotypic correlations between IP and AUDPC were tight (rg = -0.84, rp = -0.71). The genetic map encompassed 110 RFLP marker loci with an average interval length of 17 centimorgans (cM). Composite interval mapping revealed different but overlapping sets of QTL in the individual environments. In the combined analysis, 10 QTL were detected for IP and AUDPC. These included two QTL with resistance alleles coming from the susceptible parent, Lo951. Six QTL (on Chromosome 2, 3, 5, 8, 9) were associated with both traits, two affected only IP, another two only AUDPC. The QTL explained 61% of the genotypic and 52% of the phenotypic variances of IP (AUDPC: 69 and 56%). The magnitude of the individual QTL effects was homogeneous and their gene action additive. Marker-assisted improvement of NCLB resistance is considered feasible, though not necessarily economically viable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/
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  • 2
    Electronic Resource
    Electronic Resource
    Analysis of resistance to Striga hermonthica in diallel crosses of sorghum (2000)
    Springer
    Euphytica 116 (2000), S. 33-40 
    Details
    ISSN: 1573-5060
    Keywords: GCA ; SCA ; sorghum ; striga plant emergence ; striga seed germination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Parasitic flowering weeds of the genus Striga aremajor biotic constraints to sorghum (Sorghum bicolor(L.) Moench) production in sub-Saharan Africa. The agar-gel assay was used to evaluate stimulation ofStriga hermonthica (Del.) Benth. seed germination by a complete F1 diallel involving nine sorghum cultivars and inbred lines. Striga populations from Mali and Niger were employed. The same genetic materials were planted in pot trials in both countries to observe striga plant emergence. Variation in hybrid performance was determined by general (GCA) and specific combining ability (SCA) effects, with preponderance of GCA, for both germination distance in the agar-gel assay and number of emerged striga. Reciprocal effects were significant only in the agar-gel assay and were unstable across striga populations. For lines and hybrids, estimates of broad-sense heritabilities were 0.97 and 0.91 for germination distance, and 0.38 and 0.58 for emerged striga, respectively. Only a weak positive relationship existed between in vitro germination distance and emerged striga number in the pot trial. Although selection for low germination distance has merit, valuable material with resistance mechanisms other than low stimulant production may be lost if these traits are not additionally assessed. Laboratory assays which allow a non-destructive, quick and economical screening for resistance mechanisms other than the low stimulant character are likely to increase the efficiency of breeding programs for striga resistance. The significant contribution of SCA effects indicates that thorough screening of testcrosses is indispensable for selection in hybrid sorghum breeding programs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004046001009
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  • 3
    Electronic Resource
    Electronic Resource
    A gene for resistance to the maize streak virus in the African CIMMYT maize inbred line CML202 (1998)
    Springer
    Molecular breeding 4 (1998), S. 147-154 
    Details
    ISSN: 1572-9788
    Keywords: composite interval mapping ; maize streak virus ; QTL ; RFLP ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Resistance to maize streak virus (MSV) is an essential trait of improved maize varieties in sub-Saharan Africa. We mapped quantitative trait loci (QTL) for resistance to MSV in a population of 196 F2:3 lines derived from a cross between the maize inbred lines CML202 (resistant) from CIMMYT-Zimbabwe and Lo951 (susceptible) from Italy. Field tests were planted at two locations in Zimbabwe, inoculated with viruliferous leaf hoppers (Cicadulina mbila), and scored twice (21 and 83 days after infesting, DAI) on a 1–5 scale. The mean final streak intensity (score 2) of the parent lines was 2.2 (CML202) and 4.8 (Lo951). Genotype × location interaction was large for score 1 but negligible for score 2. Consequently, the heritability was higher for score 2 (0.93) than for score 1 (0.62). By composite interval mapping across locations, using a linkage map with 110 RFLP loci, four significant (LOD ≥3.0) QTL were identified for score 1 on chromosomes (C) 1, 2, 3, and 4, respectively. All four were contributed by CML202. For score 2, only the QTL on C 1 was significant (LOD =37), explaining 59% of the phenotypic and 64% of the genotypic variance. The QTL's partially dominant gene action was consistent with the nearly intermediate resistance of the F1 generation (relative heterosis for resistance 12%). The presence of one major QTL is consistent with the bimodal frequency distribution of the mapping population showing a clear 3:1 segregation. This gene seems to be allelic or identical to Msv1, a major resistance gene which was previously identified in the same genomic region in Tzi4, an inbred line from IITA. Inbred CML202 had lower final disease ratings than Tzi4. The greater resistance of CML202 may be due to allelic differences at the msv1 locus or due to the minor QTL on C 2, 3, and 4 which were not detected in Tzi4. z y Trigo (International Maize and Wheat Improvement Center); IITA, International Institute of Tropical Agriculture; IRAT, Institute de Recherches Agronomiques Tropicales et des Cultures Vivrières; KARI, Kenya Agricultural Research Institute; MSV, maize streak virus; QTL, quantitative trait locus/loci
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009602620244
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