Identification of drought, heat and combined drought and heat tolerant donors in maize (Zea mays L.)

Low maize yields and the impacts of climate change on maize production highlight the need to improve yields in eastern and southern Africa. Climate projections suggest higher temperatures within drought-prone areas. Research in model species suggests that tolerance to combined drought and heat stress is genetically distinct from tolerance to either stress alone, but this has not been confirmed in maize. In this study we evaluated 300 maize inbred lines testcrossed to CML539. Experiments were conducted under optimal conditions, reproductive stage drought stress, heat stress and combined drought and heat stress. Lines with high levels of tolerance to drought and combined drought and heat stress were identified. Significant genotype x trial interaction and very large plot residuals were observed; consequently, the repeatability of individual managed stress trials was low. Tolerance to combined drought and heat stress in maize was genetically distinct from tolerance to individual stresses, and tolerance to either stress alone did not confer tolerance to combined drought and heat stress. This finding has major implications for maize drought breeding. Many current drought donors and key inbreds used in widely-grown African hybrids were susceptible to drought stress at elevated temperatures. Several donors tolerant to drought and combined drought and heat stress, notably La Posta Sequia C7-F64-2-6-2-2 and DTPYC9-F46-1-2-1-2, need to be incorporated into maize breeding pipelines

Maize for Changing Climate - Chasing the Moving Target

The average annual growth rate of harvested maize area from 1993 to 2013 was 2.7% in Africa, 3.1% in Asia, and 4.6% in Latin America (FAOSTAT, 2018). Maize has emerged as the cereal with largest global production, which surpassed rice in 1996 and wheat in 1997, and its production is increasing at twice the annual rate of rice and three times that of wheat (Fischer et al., 2014). Among cereals, including rice, wheat and other coarse cereal, maize has recorded highest increase in area and productivity during 2006-2015 and is projected to keep the momentum during 2016-2025 (OECD/FAO, 2016). Asia, with its 31% share in global maize production from about 34.0% of the total global area harvested, is the second largest maize producer in the world. The current decade continued impressive growth in maize production, as all the sub-regions showed significant increase in maize production (Figure 1), including Southeast Asia -10.8%, Southern Asia - 27.3% and East Asia - 30.6%, which resulted in an overall 27.7% maize production increase in Asia within a short period of 2010-2016 (FAOSTAT, 2018). These gains in maize production were contributed by increase in productivity per unit area and increase in maize growing areas in some countries

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Not AvailableMost parts of the Asian tropics are hotspots of climate change effects and associated weather variabilities. One of the major challenges with climate change is the uncertainty and inter-annual variability in weather conditions as crops are frequently exposed to different weather extremes within the same season. Therefore, agricultural research must strive to develop new crop varieties with inbuilt resilience towards variable weather conditions rather than merely tolerance to individual stresses in a specific situation and/or at a specific crop stage. C4 crops are known for their wider adaptation to range of climatic conditions. However, recent climatic trends and associated variabilities seem to be challenging the threshold limit of wider adaptability of even C4 crops like maize. In collaboration with national programs and private sector partners in the region, CIMMYT-Asia maize program initiated research for development (R4D) projects largely focusing on saving achievable yields across range of variable environments by incorporating reasonable levels of tolerance/resistance to major abiotic and biotic stresses without compromising on grain yields under optimal growing conditions. By integrating novel breeding tools like - genomics, double haploid (DH) technology, precision phenotyping and reducing genotype × environment interaction effects, a new generation of maize germplasm with multiple stress tolerance that can grow well across variable weather conditions were developed. The new maize germplasm were targeted for stress-prone environments where maize is invariability exposed to a range of sub-optimal growing conditions, such as drought, heat, waterlogging and various virulent diseases. The overarching goal of the stress-resilient maize program has been to achieve yield potential with a downside risk reduction.Not Availabl