Posts Tagged ‘tropical maize’

Response to S1 recurrent selection for resistance to two stem borers, Busseola fusca and Chilo partellus, in two tropical maize populations

Posted by gabrielamartinez on , in Journal Articles

56905Authors: Mwimali, M., Derera, J., Mugo, S.N., Tongoona, P.

Published in: Euphytica, In Press.


 

Stem borers, Busseola fusca and Chilo partellus, are among the key devastating lepidopteran insect pests ofmaize causing grain yield losses.Recurrent
selection studies for stem borer resistance in maize are limited. However, maize populations carrying resistance genes to these stem borers have not been exploited fully in breeding programmes. The objective of the study was to separately improve resistance to B. fusca and C. partellus stem borers for two maize populations CML395/MBR C5 Bc and CML444/MBR/MDR C3Bc and therefore grain yield after two cycles of S1 progeny recurrent selection. Cycle 0 and the advanced generations (cycle 1-susceptible, cycle 1-resistant and cycle 2-resistant) were evaluated at three locations in Kenya using a 35 9 12 a-lattice design with 2 replications. The net reductions in cumulative tunneling, number of exit holes and leaf feeding damage scores ranged from0 to 69 %for both populations after two cycles of selection. In the two populations, each cycle of selection for borer resistance improved grain yield by 0.5–0.8 t ha-1. Actual net gains in grain yield with reference to cycle 0 were 43 % for population CML395/MBRC5 Bc under B. fusca infestation and 70 % under C. partellus infestation. For population CML444/MBR/MDR C3Bc, the actual net gains in grain yield were 25 %under B. fusca infestation and 36 % under C. partellus infestation. The reductions in the injurious effects attributable to leaf feeding damage, cumulative stem tunneling and number of exit holes contributed towards the 43 and 70 % net genetic gain in grain yield under B. fusca and C. partellus infestation respectively, for both populations. Broad sense heritability (H2) for grain yield ranged from 2 to 98 % in both maize populations. The study showed that two cycles of S1 progeny recurrent selection was effective in accumulating favourable alleles for B. fusca and C. partellus stem borer resistance.

Genetic diversity of tropical early-maturing maize inbreds and theirperformance in hybrid combinations under drought and optimum growing conditions

Posted by gabrielamartinez on , in Journal Articles

56902Authors: Oyekunle, M., Badu-Apraku, B., Franco, J., Hearne, S.

Published in: Field Crops Research 2014, vol. 170, p. 55-65.


 

Hybrid development is enhanced by the assessment and understanding of genetic diversity and dis-tance within inbreds. One hundred and fifty hybrids derived from 30 early-maturing inbreds plus sixchecks were evaluated at three locations in Nigeria for 2 years to assess their performance under droughtand well-watered conditions. In addition, twenty three microsatellite markers were employed to assessgenetic diversity of selected 42 inbreds. Significant differences were observed among inbreds and hybridsfor most traits under both research conditions. A total of 130 alleles were detected ranging from two fornc133 to nine for phi299852 with an average of 5.7 alleles per locus. Polymorphic information contentranged from 0.17 for phi308707 to 0.77 for phi084 with an average of 0.54. Thirty-one unique alleleswere detected in 21 inbreds. Microsatellite markers classified the inbred lines into five groups. Geneticdistance estimates among pairs of inbreds ranged from 0.42 (TZEI 26 vs TZEI 108) to 0.85 (TZEI 24 vs TZEI4) with an average of 0.67. Correlation between microsatellite-based GD estimates of the parental linesand their F1hybrids were not significant for grain yield and other traits under drought and well-wateredconditions. However, significant correlations existed between F1hybrid grain yield and heterosis underdrought and well-watered conditions. TZEI 31 × TZEI 18 was identified as the highest-yielding and stablehybrid across environments and should be promoted for adoption by farmers in West and Central Africa.

Early vertical distribution of roots and its association with drought tolerance in tropical maize

Posted by Carelia Juarez on , in Journal Articles

Published in Plant and Soil 377 (1-2295-308, 2014

Grieder, C.; Trachsel, S.;Hund, A.

Background and aims: Selection for deep roots to improve drought tolerance of maize (Zea mays L.) requires presence of genetic variation and suitable screening methods.

Methods: We examined a diverse set of 33 tropical maize inbred lines that were grown in growth columns in the greenhouse up to the 2-, 4-, and 6-leaf stage and in the field in Mexico. To determine length of roots from different depths at high throughput, we tested an approach based on staining roots with methylene blue and measuring the amount of absorbed dye as proxy measure for root length.

Results: Staining provided no advantage over root weights that are much easier to measure and therefore preferable. We found significant genotypic variation for all traits at the 6-leaf stage. For development rates between the 2-leaf and the 6-leaf stage, genotypes only differed for rooting depth and the number of crown roots. Positive correlations of leaf area with root length and rooting depth indicated a common effect of plant vigor. However, leaf area in growth columns was negatively related to grain yield under drought (r = −0.50).

Conclusion: The selection for deeper roots by an increase in plant vigor likely results in a poorer performance under drought conditions. The proportion of deep roots was independent of other traits but showed a low heritability and was not correlated to field performance. An improved screening protocol is proposed to increase throughput and heritability for this trait.

QTL mapping in three tropical maize populations reveals a set of constitutive and adaptive genomic regions for drought tolerance

Posted by Carelia Juarez on , in Journal Articles

Published in Theoretical and Applied Genetics, 2012

Gustavo Dias Almeida, Dan Makumbi, Cosmos Magorokosho, Sudha Nair, Aluízio Borém, Jean-Marcel Ribaut, Marianne Bänziger, Boddupalli M. Prasanna, Jose Crossa and Raman Babu

Despite numerous published reports of quantitative trait loci (QTL) for drought-related traits, practical applications of such QTL in maize improvement are scarce. Identifying QTL of sizeable effects that express more or less uniformly in diverse genetic backgrounds across contrasting water regimes could significantly complement conventional breeding efforts to improve drought tolerance. We evaluated three tropical bi-parental populations under water-stress (WS) and well-watered (WW) regimes in Mexico, Kenya and Zimbabwe to identify genomic regions responsible for grain yield (GY) and anthesis-silking interval (ASI) across multiple environments and diverse genetic backgrounds. Across the three populations, on average, drought stress reduced GY by more than 50 % and increased ASI by 3.2 days. We identified a total of 83 and 62 QTL through individual environment analyses for GY and ASI, respectively. In each population, most QTL consistently showed up in each water regime. Across the three populations, the phenotypic variance explained by various individual QTL ranged from 2.6 to 17.8 % for GY and 1.7 to 17.8 % for ASI under WS environments and from 5 to 19.5 % for GY under WW environments. Meta-QTL (mQTL) analysis across the three populations and multiple environments identified seven genomic regions for GY and one for ASI, of which six mQTL on chr.1, 4, 5 and 10 for GY were constitutively expressed across WS and WW environments. One mQTL on chr.7 for GY and one on chr.3 for ASI were found to be ‘adaptive’ to WS conditions. High throughput assays were developed for SNPs that delimit the physical intervals of these mQTL. At most of the QTL, almost equal number of favorable alleles was donated by either of the parents within each cross, thereby demonstrating the potential of drought tolerant × drought tolerant crosses to identify QTL under contrasting water regimes.

 

Quality control genotyping for assessment of genetic identity and purity in diverse tropical maize inbred lines

Posted by Carelia Juarez on , in Journal Articles

Published in Theoretical and Applied Genetics, 2012

Kassa Semagn, Yoseph Beyene, Dan Makumbi, Stephen Mugo, B. M. Prasanna, Cosmos Magorokosho and Gary Atlin

Quality control (QC) genotyping is an important component in breeding, but to our knowledge there are not well established protocols for its implementation in practical breeding programs. The objectives of our study were to (a) ascertain genetic identity among 2–4 seed sources of the same inbred line, (b) evaluate the extent of genetic homogeneity within inbred lines, and (c) identify a subset of highly informative single-nucleotide polymorphism (SNP) markers for routine and low-cost QC genotyping  and suggest guidelines for data interpretation. We used a total of 28 maize inbred lines to study genetic identity among different seed sources by genotyping them with 532 and 1,065 SNPs using the KASPar and GoldenGate platforms, respectively. An additional set of 544 inbred lines was used for studying genetic homogeneity. The proportion of alleles that differed between seed sources of the same inbred line varied from 0.1 to 42.3 %. Seed sources exhibiting high levels of genetic distance are mis-labeled, while those with lower levels of difference are contaminated or still segregating. Genetic homogeneity varied from 68.7 to 100 % with 71.3 % of the inbred lines considered to be homogenous. Based on the data sets obtained for a wide range of sample  sizes and diverse genetic backgrounds, we recommended a subset of 50–100 SNPs for routine and low-cost QC genotyping, verified them in a different set of double haploid and inbred lines, and outlined a protocol that could be used to minimize errors  in genetic analyses and breeding.