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CIMMYT and IITA breeding programs are selected for tolerance to important biotic stresses (GLS, MSV,
ear rots, Striga, turcicum leaf blight and rusts, among others). Past maize research at CIMMYT and IITA
has tended to focus on the early stages of quantitative trait locus (QTL) mapping for biotic stresses, but
stopped short of delivering the validated, tightly linked or gene‐based markers needed to breed
efficiently for biotic stress tolerances that are oligogenically inherited. This SI will prioritize the finemapping
and positional cloning work needed for development of breeder‐ready, low‐cost SNP markers
for resistance to MSV, GLS, E. turcicum, and other key adaptive diseases (BLSB, PFSR, downy mildews),
allowing the rapid introgression of an appropriate suite of resistances into stress‐tolerant lines.
Efforts to identify donor germplasm and tagged alleles conferring resistance to yield‐limiting leaf and ear
diseases need to be increased, especially for emerging diseases (tar spot in Latin America; BLSB in Asia),
for which little breeding work has been done. CIMMYT, IITA, NARS, and private‐sector programs need to
join forces to ensure effective hot‐spot and inoculated screening for donor identification, and to share
the cost and effort required to develop production markers for both oligogenically and polygenically
controlled biotic stress resistances. Significant progress has been made to identify stable genetic
resistance for most major maize diseases and for Striga (Gerpacio and Pingali 2007; Lal et al. 2000;
Bosque‐Perez 2000; Pratt and Gordon 2006; Menkir et al. 2007; Welz & Geiger 2000).
Available sources of resistance must be confirmed in multiple environments to facilitate identification of
the most suitable resistance genes and donors for use in breeding programs. CIMMYT has started
multilocation phenotyping of elite inbred lines for response to several diseases of economic importance,
including GLS, E. turcicum, MSV; ear rots, southern corn leaf blight, and southern and common rusts.
Preliminary results have identified several good sources of resistance for all diseases and across
locations. Maize inbred lines with diverse genetic backgrounds and differential disease reaction patterns
developed at CIMMYT and IITA will form an association panel for testing in multiple locations in sub‐
Saharan Africa. Similar efforts are being planned for regionally important diseases such as bacterial leaf
and sheath blight and downy mildew and PFSR in India.
Progress in breeding for host plant resistance to economically important insects has been slower than
breeding for disease resistance. However, CIMMYT and IITA have developed several insect‐resistant
populations (to stem borer and storage pests) which have been successfully used in Kenya and Nigeria
and can be used to introgress insect resistance into agronomically elite materials with high levels of
abiotic stress tolerance and high yield potential. Several inbred lines have been developed combining
resistance to stem borers and storage pests. Wide testing of these materials in Kenya, Tanzania, and
Uganda is taking place as part of the Insect Resistant Maize for Africa (IRMA) project, resulting in the
release of insect‐resistant hybrids. Efforts are being made to combine insect resistance and drought
tolerance, using doubled haploid technology to rapidly develop inbred lines combining insect and
drought tolerance. Identification of QTLs and associated gene‐based markers for resistance will facilitate
the rapid conversion of agronomically elite inbred lines to higher levels of tolerance.
Current approaches to improve insect and disease resistance at IITA, CIMMYT, and in national programs
are based largely on phenotypic selection and have resulted in populations with improved resistance to
MSV, leaf disease and storage insects. However, these approaches are inefficient when inoculated
screening is unreliable or expensive and natural occurrence of the stress is intermittent. They are also
slow and expensive when the objective is to convert elite, drought‐tolerant inbreds to higher levels of
tolerance. Quantitative trait loci (QTL) associated with resistance to many diseases (NLB, downy mildew,
SLB, rust, GLS, and many other diseases) and insects have been identified and mapped in maize (Wisser
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