Abstract
Maize (Zea mays L.) is the staple food in Kenya, and mapping the qualitative trait loci (QTL) associated with resistance to maize stem borer pest is important towards marker assisted breeding for this quantitative trait. The objective of this study was to identify any QTL associated with resistance to Chilo partellus and Busseola fusca, the two important stem borer pests in maize production in Kenya. A total of 203 F2:3 individuals from a cross between CML442, a stem borer susceptible maize inbred line and CKSBL10026, a stem borer resistant maize inbred line; and 152 SNPs were used for mapping the QTL. Data were collected on leaf damage, stem borer exit holes and stem tunneling length as putative stem borer damage traits. A likelihood odds ratio (LOD) scores of 3.0 and maximum recombination frequency of 0.50 were used to declare linkage. LOD scores between 2.5 and 2.9 were considered strong indications of a QTL. Resistance QTL for the three putative traits were detected on chromosomes 1-7 and 9 for both individual locations and stem borer species analysis. In B. fusca sites, one QTL for reduced stem tunnelling was revealed on chromosome 4 while in the C. partellus sites, one QTL for reduced stem tunnelling was identified on chromosome 4 and another for reduced stem borer exit holes was identified on chromosome 5. Phenotypic variances explained ranged from 6 to 10%, suggesting a need to validate these QTL using a larger population and in different environments. Key words: Busseola fusca, Chilo partellus, mapping, quantitative trait loci (QTL), resistance, single nucleotide polymorphisms (SNPs), stem borer.
Highlights
Insect pests affect 46% of global maize growing area causing about 24.5% of world maize loss annually
In B. fusca sites, one qualitative trait loci (QTL) for reduced stem tunnelling was revealed on chromosome 4 while in the C. partellus sites, one QTL for reduced stem tunnelling was identified on chromosome 4 and another for reduced stem borer exit holes was identified on chromosome 5
Heritability for resistance traits based on combined sites analysis was low for both stem borer species but high when estimated for evaluations at individual sites except at Mtwapa (Table 2)
Summary
Insect pests affect 46% of global maize growing area causing about 24.5% of world maize loss annually. Maize stem borer species are the primary field pests that feed on leaves, cob and pith resulting in stem damage and grain yield losses in the entire world wherever maize is grown (Mihm, 1997; Samayoa et al, 2015a). The stem borers are some of the major pests that account for the low maize production, with lepidopteran stem borers, including the African stem borer (Busseola fusca Fuller), the spotted stem borer (Chilo partellus Swinhoe) and the pink stem borer (Sesamia Calamistis Hampson) being the most damaging pests in eastern and southern Africa, where they cause 13 to 40% yield losses (De Groote, 2002; Mailafiya et al, 2011). In Kenya, the major maize stem borer species are C. partellus, B. fusca and S. calamistis. C. partellus is found in the warmer and lower areas, B. fusca is predominant in the cooler and higher altitudes areas while S. calamistis is found in low densities in all ecologies in Kenya (Ong‘amo et al, 2006)
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