Partitioning and Passion, Potholes and Partnerships: A Journey with Tropical Maize

By the mid-1970s it was clear that tropical maize was very susceptible to drought that coincided with flowering, and a program to improve its tolerance was launched at CIMMYT, Mexico. Yield gains from selecting for an index comprising grain yield plus secondary traits under managed drought stress in Mexico were significant and immediate, and did not reduce yield potential. Progress from recurrent selection in one population was soon followed by selection in five others as methods were refined. Yield gains under a range of drought severity averaged around 100 kg ha^-1 yr^-1 or 3-5% per year. Gains in each population were from increased frequency of alleles imparting tolerance, though new sources of drought tolerant inbreds were also generated. Selection resulted in changed partitioning that favored ear growth and kernel set under stress, and resulted in rapid silk growth and a short anthesis-silking interval. A similar pattern of response, though less dramatic, was observed under low nitrogen. After careful validation in the mid 90’s, the methodology moved to southern Africa, a region plagued by severe and unpredictable drought. Later, through the generosity of key donors, similar methods were applied to germplasm adapted to much of sub-Saharan Africa. Today 368 drought tolerant hybrids and OPVs producing 65,000 tons of certified maize seed/year are deployed in that region alone. Key factors leading to the success of this program are: the vision of founding CIMMYT staff; continuity of support by program leaders and donors for over 40 years; an array of talented young scientists who believed passionately that they could make a difference; and excellent partnerships with national research programs and seed companies who are increasingly leading initiatives in product development and adoption. Additional lessons learned, and implications for temperate maize will also be discussed during the presentation.