Abstract
One hundred maize inbred lines and eighty four hybrids were characterized for resistance to maize stem borer and post-harvest insect pests. This was achieved using genetic distance and population structure based on simple sequence repeat (SSR) markers and biophysical traits. The test materials were evaluated for stem borer, maize weevil and larger grain borer (LGB) resistance. Leaf samples were harvested from 10 healthy plants per genotype and bulked. Genomic DNA was extracted using a modified version of mini-prep Cetyl Trimethyl Ammonium Bromide (CTAB) method. The samples were genotyped with 55 SSRs makers. Univariate analysis of variance was done using the general linear model procedure of SAS statistical package. Rodgers genetic distance was calculated for all data sets as a measure of genetic distance using NTSYS-pc for Windows. The distance matrices were used to generate phenograms using the unweighted pair group method based on arithmetic average (UPGMA) method in MEGA5. The genotypes were assigned into different populations using population structure software. The data was further subjected to discriminant and principal component analysis to group the gnotyoes. Analysis of molecular variance within and among the different populations was done using arlequin. There were significant differences (P ≤ 0.001) for all the biophysical traits evaluated. The SSR marker data estimated successfully the close relationship among different hybrids and inbred lines within clusters. Comparisons of the different multivariate analyses revealed high concordance among the different approaches of analyses. The results of this study can be directly used by breeding programs to develop resistant genotypes.
Highlights
Maize is a staple food for more than 300 million people in sub Saharan Africa (SSA) and is commonly grown by small-scale and resource poor farmers in rural areas (Shiferaw et al, 2011)
There are different possible methods that help in minimizing yield loss by insect pest, host plant resistance developed through breeding is a preferred method to disseminate improved maize varieties due to its environmental and human safety, relatively low cost, and ease of use by farmers
simple sequence repeat (SSR) makers are widely used by maize researchers because they are available in large numbers in the public domain (MaizeGDB: http://www.maizegdb.org), co-dominant, multiallelic, highly polymorphic even in closely related individuals, can be exchanged between laboratories, and have uniform distribution in the genome (Gupta et al, 2002; Prasanna et al, 2010)
Summary
Maize is a staple food for more than 300 million people in sub Saharan Africa (SSA) and is commonly grown by small-scale and resource poor farmers in rural areas (Shiferaw et al, 2011). The average maize yield in SSA was estimated at 1.4 t/ha, which is extremely low as compared to the 3.3 t/ha reported in developing countries in other parts of the world, the 4.9 t/ha worldwide production and the 8.4 t/ha in industrialized countries. Maize stem borers cause maize losses of up to 15% in susceptible germplasm in the infested ecologies, while the storage pest, such as maize weevil and larger grain borer (LGB). There are different possible methods that help in minimizing yield loss by insect pest (e.g. chemical, biological and cultural methods), host plant resistance developed through breeding is a preferred method to disseminate improved maize varieties due to its environmental and human safety, relatively low cost, and ease of use by farmers. Some of the MBR germplasm have been released and disseminated in some countries
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