Maize long-term genetic progress explains current dominance over sorghum in Argentina

Abstract

Sorghum (Sorghum bicolor L. Moench) is traditionally known for its better adaptation to drought when compared to other cereals like maize (Zea mays L.). However, genetic gains are significantly higher for maize than for sorghum, and are known to include drought tolerance. We analyzed maize and sorghum harvested area, yield, and yield stability using publically available farm data from 1970 to 2016 in Argentina, where both crops are sown across a large environmental gradient (water balance from ca.−400 to −1100 mm year−1). Yield stability was assessed by analyzing county yield residuals relative to average yields. Both crops had comparable yields in 1970, but showed a different yield progress (ca. 110 kg ha−1 year−1 or 1.73 % year−1 and 62 kg ha−1 year−1 or 1.26 % year−1 for maize and sorghum, respectively). Yield difference in favor to maize became more evident since late 90´s, together with the introduction of genetically modified (GM) materials in this crop. Today this consistent maize yield advantage over sorghum is observed across all regions, even those with more frequent water shortages. It also impacted in the maize area, being 6-fold larger than that of sorghum in 2016. Sorghum yield stability was traditionally higher than that of maize (maize yield relative residuals were 4–15 % higher than that of sorghum), but today both crops have similar yield stability in most regions. Yield progress showed comparable rates to reported genetic gains for maize (0.85–1.74 % year−1), but not for sorghum (0.09 % year−1). The contrasting investment in breeding, GM traits, and agronomy explains major differences between crops, and can be extrapolated to other countries where both crops have differential genetic yield gains. Sorghum yield stability is desirable in marginal areas, but alternative benefits (higher residue, non-GM gluten free grain for specialty markets) might be more important in the future for promoting this crop.