Challenges of Maize Breeding Under Tropical Conditions of Brazil

Abstract

Tropical maize production represents 49% of the global maize harvested area. In terms of productivity, the annual increase rate in tropical regions is twice as higher as the increase rate in temperate regions. The increase in maize grain yield was expressive in the last 41 years in Brazil. Such achievement was possible due to the joint efforts of many areas of science, especially, plant breeding. Although maize breeding success, many are the challenges faced by the maize breeders to develop high-yielding maize hybrids. Tropical conditions provide more intense challenges in terms of pests and diseases pressures, and above all, water deficit conditions. In addition, the constant increase of breeding programs costs requires the development and application of new techniques to improve the genetic gain per time unit, increasing the maize breeding programs’ efficiency. This review discusses the main challenges faced by maize breeding programs under tropical conditions, highlighting topics related to the development of maize hybrids for first and second growing seasons; breeding for biotic and abiotic stresses conditions; specialty maize breeding; use of transgenic in maize; and genomic tools to maximize the efficiency of maize breeding programs under tropical conditions.

Assessment of yield performance and stability of hybrids and populations of tropical maize across multiple environments in Southeastern Brazil

“…Drought, low N, and high nighttime temperature conditions are the major abiotic factors limiting the yield of maize in tropical environments (Boomsma et al., 2009; Durães, 2014; Edmeades et al., 2017; Nurmberg et al., 2022; Von Pinho et al., 2022). Low N is considered the second most limiting factor to maize yield, and the effects of low N stress on maize yield appear to be more intense under drought stress than under optimum moisture since N is transported in the soil mainly by mass flow and therefore is highly soil water dependent (Bänziger, 2000; Barber & Cushman, 1981; DeBruin & Butzen, 2014).…”

“…In relation to heat stress, high temperature negatively affects maize growth, development, and yield mainly in lowland tropical environments (0–600 m above sea level, asl), which are characterized by lower solar radiation and high night temperature, that is, lower diurnal temperature amplitude, especially during the maize grain filling stage (Durães, 2014; Fancelli, 2017; Prasanna et al., 2021; Von Pinho et al., 2022). High night temperature associated with lower diurnal temperature amplitude during maize flowering and post‐flowering resulted in increases in night respiration and reductions in photosynthesis, crop growth rate, kernel number, and grain yield (Alam et al., 2017; Hussain et al., 2019; Kettler et al., 2022; Wang et al., 2020).…”

“…During the 2020/21 season, Brazilian maize production was significantly affected by drought occurrence during the reproductive phase of maize, and the amount of harvested maize was reduced by approximately 15.00 million metric tons, which represented a decline of 16% compared with 2019/20 maize production (CONAB, 2022). Drought, low N, and high nighttime temperature conditions are the major abiotic factors limiting the yield of maize in tropical environments (Boomsma et al, 2009;Durães, 2014;Edmeades et al, 2017;Nurmberg et al, 2022;Von Pinho et al, 2022). Low N is considered the second most limiting factor to maize yield, and the effects of low N stress on maize yield appear to be more intense under drought stress than under optimum moisture since N is transported in the soil mainly by mass flow and therefore is highly soil water dependent (Bänziger, 2000;Barber & Cushman, 1981;DeBruin & Butzen, 2014).…”

“…In the presence of genotype by environment interaction (GEI), different cultivars respond differently to diverse environments, and consequently, the rank of cultivars may vary in different environments, complicating the identification of maize cultivars across multiple environments (De Leon et al., 2016; El‐Soda et al., 2014; Haldane, 1946; Yan, 2016). In tropical environments, the GEI tends to be stronger than in non‐tropical environments due to the more pronounced and frequent occurrence of abiotic stress, such as drought, heat, and low N (Edmeades et al., 2017; Nurmberg et al., 2022; Von Pinho et al., 2022). Consequently, maize cultivars must be evaluated across multiple tropical environments before their recommendation and release for farmers.…”