Dagne Wegary

The Influence of Water Stress on Yield and Related Characteristics in Inbred Quality Protein Maize Lines and Their Hybrid Progeny

Water stress is one of the factors most frequently limiting maize production, food security, and economic growth in sub-Saharan Africa. The unprecedented combination of climatic risk, declining soil fertility, the need to expand food production into more marginal areas as population pressure increases, high input costs, extreme poverty, and unavailability of credit systems, have resulted in small holder farmers in southern and eastern Africa producing maize in extremely low-input/low risk systems (Banziger and Diallo, 2004). As a consequence, crop yields are falling to very low levels and food insecurity is widespread amongst agricultural communities (Kamara et al., 2004). The development of maize germplasm able to tolerate water stress is crucial if the productivity of maize based farming systems is to be sustained or increased (Betran et al., 2003). Maize genotypes perform differently under water stress conditions due to the existence of genetic variability for tolerance to stress (Bolanos and Edmeades, 1993; Lafitte and Edmeades, 1994; Banziger et al., 2000; 2006; Diallo et al., 2004). Betran et al. (2003) observed hybrids performing well under stress and suggested the possibility of combining stress tolerance and yield potential in tropical maize hybrids. Tolerance of maize to water stress is partly related to the development of the root system, which in turn influences water and nutrient uptake by crop plants (Moll et al., 1982; Kamara et al., 2004). In general, however, the amount of grain yields recorded from maize genotypes fall with the severity of water stress (Betran et al., 2003). Breeding strategies to develop stress tolerant maize inbred lines include screening and selection of inbreds under managed stress conditions, multi-location testing of progeny in a representative sample of the target environments, and selection under high plant populations (Beck et al., 1997). Additional information from adaptive secondary traits (ears per plant, anthesis-silking interval and leaf senescence) that show differential expression between optimal and stress conditions is genetically variable and is correlated with grain yield and is commonly used to increase selection efficiency (Bolanos and Edmeades, 1993; 1996; Banziger and Lafitte, 1997). When genetic variance and

Genetic variation and population structure of maize inbred lines adapted to the mid-altitude sub-humid maize agro-ecology of Ethiopia using single nucleotide polymorphic (SNP) markers

BackgroundMolecular characterization is important for efficient utilization of germplasm and development of improved varieties. In the present study, we investigated the genetic purity, relatedness and population structure of 265 maize inbred lines from the Ethiopian Institute of Agricultural Research (EIAR), the International Maize and Wheat Improvement Centre (CIMMYT) and the International Institute of Tropical Agriculture (IITA) using 220,878 single nucleotide polymorphic (SNP) markers obtained using genotyping by sequencing (GBS).ResultsOnly 22% of the inbred lines were considered pure with <5% heterogeneity, while the remaining 78% of the inbred lines had a heterogeneity ranging from 5.1 to 31.5%. Pairwise genetic distances among the 265 inbred lines varied from 0.011 to 0.345, with 89% of the pairs falling between 0.301 and 0.345. Only <1% of the pairs had a genetic distance lower than 0.200, which included 14 pairs of sister lines that were nearly identical. Relative kinship analysis showed that the kinship coefficients for 59% of the pairs of lines was close to zero, which agrees with the genetic distance estimates. Principal coordinate analysis, discriminant analysis of principal components (DAPC) and the model-based population structure analysis consistently suggested the presence of three groups, which generally agreed with pedigree information (genetic background). Although not distinct enough, the SNP markers showed some level of separation between the two CIMMYT heterotic groups A and B established based on pedigree and combining ability information.ConclusionsThe high level of heterogeneity detected in most of the inbred lines suggested the requirement for purification or further inbreeding except those deliberately maintained at early inbreeding level. The genetic distance and relative kinship analysis clearly indicated the uniqueness of most of the inbred lines in the maize germplasm available for breeders in the mid-altitude maize breeding program of Ethiopia. Results from the present study facilitate the maize breeding work in Ethiopia and germplasm exchange among breeding programs in Africa. We suggest the incorporation of high density molecular marker information in future heterotic group assignments.

Evaluation of quality protein maize inbred lines for resistance to maize weevil Sitophilus zeamais (Coleoptera: curculionidae) and other important agronomic traits

Searching new sources of resistance to the maize weevil are critical in a successful breeding program to address grain damage by postharvest pests. This study was undertaken to evaluate resistance in 28 quality protein maize (QPM) inbred lines against Sitophilus zeamais infestation and their important agronomic attributes, and consequently their value for use in breeding programs to develop resistant QPM hybrids. Susceptibility index (SI), which considers the progeny number in the F1 generation and the time the insects take to mature from egg to adult, was used to measure the susceptibility. Out of the 28 inbred lines tested, one inbred line (CML-142) was resistant, three (CML-144/144-7-b (F2)-4-2-1-1-1-1-1, POOL 15QPFS-693-B-2-B-#-B-B-B-# and CML-149) were moderately resistant and the remaining 24 inbred lines were categorized as susceptible to highly susceptible. Importantly, those inbred lines that are resistant and moderately resistant had better yield and other agronomic performances as compared to the susceptible ones. These resistant and moderately resistant inbred lines showed considerable reduction in grain damage and losses for S. zeamais, suggesting that they contained genes that confer resistance to the pest. Correlations between kernel size, breadth and texture with some important susceptibility parameters were found to be significant, indicating possible influence of these factors together with others in determining the susceptibility of the QPM inbred lines to S. zeamais. Identification of QPM lines resistant to S. zeamais in the present study offers an opportunity to breed for resistance to maize weevil in developing QPM hybrid with enhanced resistance to S. zeamais.

Genetic relationships and heterotic structure of quality protein maize (Zea mays L.) inbred lines adapted to eastern and southern Africa

Information on heterotic patterns of quality protein maize (QPM) inbred lines would help to design appropriate breeding strategies for QPM. The objectives of this study were to assess the genetic relationships and heterotic structure of elite QPM inbred lines adapted to eastern and southern Africa (ESA) using simple sequence repeat (SSR) markers. Thirty-five inbred lines consisting of 32 QPM and three non-QPM inbred lines were genotyped using 40 SSR markers that yielded a total of 217 alleles, with an average of 5.43 and range of 2–10 alleles per marker. The number of alleles per inbred line varied from 40 to 82, with a mean of 51.5. About 81% of the pairwise comparisons between the lines had genetic distance estimates varying from 0.250 to 0.415. The unweighted paired group method using arithmetic averages (UPGMA) clustering algorithm and model-based population structure analysis showed the presence of two to three major groups, mainly consistent with maturity groups and pedigree information. This information can facilitate effective utilization of the QPM inbred lines in breeding programs.

Evaluation of quality protein maize inbred lines for resistance to Turcicum leaf blight and grey leaf spot disease under field condition at mid altitude sub-humid agro-ecology of Ethiopia

Grey Leaf Spot and Turcicum Leaf Blight, severe foliar diseases of maize caused by the fungi Cercospora zeamaydis and Exserohilum turcicum, are characterized by relatively rapid leaf necrosis and premature death of foliage which reduces grain yield of maize crop in Ethiopia, the diseases become a major problem in all major maize growing areas. The study was carried out with the objective to evaluate and identify resistant/tolerant quality protein maize inbred lines to turcicum leaf blight and grey leaf spot diseases. A total of 25 QPM inbred lines were evaluate and necessary data on incidence, disease severity, AUDPC, plant height and grain yield were recorded. Result of combined analysis variance showed significant (p<0.05) difference of year x inbred lines interaction for TLB and GLS severity. The performances of the inbred lines were not consistent across years as evident from the significant year x genotypes interactions. Out of twenty five quality protein inbred lines, four of them showed resistant to turcicum leaf blight and three inbred lines resistance to grey leaf spot disease. The majority of quality protein inbred lines were showed moderate resistant to both diseases. Some quality protein maize inbred lines resistance to both diseases, indicating that it can carry genes for multiple traits. However, further study required through fine mapping and identification of co-located QTLs. Overall, the identified resistance inbred lines can be utilized in future maize breeding program like for possible use of introgression into cultivars, as source of donor and varietal resistance development.