Drought, like many other environmental stresses, has adverse effects on crop yield including maize (Zea mays L.). Low water availability is one of the major causes for maize yield reductions affecting the majority of the farmed regions around the world. Therefore, the development of drought-tolerant lines becomes increasingly more important. In maize, a major effect of water stress is a delay in silking, resulting in an increase in the anthesis-silking interval, which is an important cause of yield failures. Diverse strategies are used by breeding programs to improve drought tolerance. Conventional breeding has improved the drought tolerance of temperate maize hybrids and the use of managed drought environments, accurate phenotyping, and the identification and deployment of secondary traits has been effective in improving the drought tolerance of tropical maize populations and hybrids as well. The contribution of molecular biology will be potential to identify key genes involved in metabolic pathways related to the stress response. Functional genomics, reverse and forward genetics, and comparative genomics are all being deployed with a view to achieving these goals. However, a multidisciplinary approach, which ties together breeding, physiology and molecular genetics, can bring a synergistic understanding to the response of maize to water deficit and improve the breeding efficiency.

Experimentally induced introgression and selection during domestication and maize (Zea mays L.) improvement involved selection of specific alleles at genes controlling morphological and agronomic traits, resulting in reduced genetic diversity relative to unselected genes. The plant breeder would have to extend crosses to the wild relatives to introduce novel alleles and diversify the genetic base of elite breeding materials. The use of maize wild relatives (Teosintes and Tripsacum) genes to improve maize performance is well established with important examples dating back more than 60 years. In fact, Teosintes and Tripsacum are known to possess genes conferring tolerance to several biotic and abiotic stress including chlorotic dwarf virus, downy mildew, Fusarium, Striga hermonthica, rootworms, drought and flooding. This review provides an overview of the application of these wild relatives and demonstrates their roles on the development of stress tolerant maize plants. It also highlights the use of Teosintes and Tripsacum to improve selected quantitative traits such as yield.

Wild relatives possess potential genetic diversity for maize (Zea mays L.) improvement. Characterization of maize-mexicana introgression lines (ILs) is of great value to diversify the genetic base and improve the maize germplasm.Four maize-mexicana IL generations, i.e. BC1, BC2, BC3, and RIL, were constructed under the elite inbred background of 48-2, elite inbred line that is widely used in maize breeding in Southwestern China, and were phenotyped in different years and genotyped with 56110 SNPs. The results indicated that 48-2 had higher phenotypic performances than all the characterized ILs on most of the agronomic traits. Compared with other ILs, BC2 individuals exhibited more similar performance to 48-2 on most traits and possessed the highest kernel ratio (66.5%). Population structure and principal component analysis indicated that BC3 individuals gathered closer to 48-2 and exhibited the lowest mexicana-introgression frequency (0.50%), while BC2 (29.06%) and RIL (18.52%) showed higher introgression frequency. The high level of genetic diversity observed in the maize-mexicana ILs demonstrated that Z. mays ssp. mexicana can serve as a potential source for the enrichment of maize germplasm.