b'improvements to drought tolerance without compromising over-all productivity. We have had success using molecular breeding and prediction for complex traits dealing with the multitude of mechanisms that come together to provide drought tolerances such as root development, limited transpiration, response to humidity, water balance, reproductive resilience, or ears that can hold more kernels.Messina says a joint study conducted by Corteva, the Phenotype Screening Corporation, the University of Kentucky and the University of Queenslands Alliance for Agriculture and Food Innovation published in May 2021 in the Journal of Experimental Biology, investigated the proposal that changes in root systems architecture (RSA) might underpin the 3-fold increase in maize grain yield over the last century.The researchers found that both RSA and yield have changed with decades of maize breeding, but not the crop water uptake. The results from X-ray phenotyping showed that single crossThanda Dhliwayo. Qingwu Xue.hybrids have smaller root systems than double cross hybrids and that yield and yield components were higher for single crosses than double crosses across densities and irrigation. Taken together, the results suggest that changes in RSA were not the cause of increased water uptake, but an adaptation to high-den-sity stands used in modern agriculture. The researchers add that advances in root physiology and phenotyping can create opportunities to maintain long-term genetic gain in maize, but a shift from ideotype to crop and pro-duction system thinking will be required.Drought is a complex problem and breeding by dealing with multiple mechanisms is more effective than pursuing one-trait solutions, Messina says. Days are becoming warmer and drier, and we need to develop varieties that can deal with that. New techniques are making it more effective to create new genetic material through recombination that increases the number of crosses that can be made. Breeding Methods Old and NewTraditionally, breeding for drought stress tolerance employs the use of natural genes found in landraces, crop wild relativesMatt Reynolds.and neglected and underutilized species (NUS) and introducing them into existing cropping systems.Traits and alleles are combined strategically into already val- 97%, with 9% monocot and 38% dicot. Bacterial genes com-uable genetic backgrounds so they can be readily used by publicprised 1.5% and fungi 1.2%. Of the plant genes, maize genes were and private breeders globally, says Reynolds. Novel lines based53% with the next three top species being Arabidopsis (37%), on these approaches are in high demand from public and privaterice (6%) and sorghum (1.8%).breeders of the International Wheat Improvement Network. The authors reported that some genes performed positively Untempered by social and/or political constraints thatin one hybrid, neutral or even negative in another hybrid combi-currently prevent public wheat breeding programs from uti- nation, demonstrating the value of value of top-cross testers to lizing newer genetic tools, the private corn seed sector hasproperly evaluate promising leads. The corollary, they noted, is made significant strides in crop improvement using transgenicthat some number of genes likely did not perform well in primary approaches in the development of drought tolerances. tests because of negative interactions with that germplasm pos-Messina says that biotechnology has been instrumental insibly obscuring the genes potential.Cortevas ability to improve corn agronomic traits such as yield,Field testing is admittedly expensive and time-consuming. nitrogen use efficiency and drought tolerance.The authors highlighted a few criteria for successful field testing. For the multi-year transgene study (2010-2018), the authors,First, define the desired effect size. Given the lengthy road to current and former Corteva scientists, field tested a total of 1,671market, the effect should be large enough to increase elite germ-unique genes sourced from 47 species. Plant genes comprisedplasm yield, often some 20 years hence.58/ SEEDWORLD.COMSEPTEMBER 2021'