Plant growth regulators ameliorate or exacerbate abiotic, biotic and combined stress interaction effects on Zea mays kernel weight with inbred-specific patterns

Plant growth regulators have documented roles in plant responses to single stresses. In combined-stress environments, plants exhibit novel genetic architecture for growth traits and physiological responses can display synergistic effects. Synergistic responses have been used to optimize agronomic production and recommendations for adaptation to weather and field conditions can be used to improve selective breeding for higher yielding crops. We hypothesized that alterations in hormone balance would alter phenotypic responses to abiotic and crowding stress in a genotype-specific manner. We investigated the role of plant growth regulators in modulating combined-stress growth responses in Zea mays. Maize inbreds were exposed to all single, double and triple combinations of the following stressors in a field environment: drought, nitrogen deprivation, and increased plant density. Growth regulator chemical treatments were applied in a factorial design using a range of inbred genotypes. We found significant differences between the seed weights of plants given different chemical treatments and when single-stress environments were compared to combined stress environments. Different inbred genotypes exhibited contrasting patterns of response to combined stress and plant growth regulator treatment. Plant growth regulators altered combined-stress response pathways in maize inbreds; predictions of growth regulator effects would be improved by better characterization of stress environments and genotype-environment interactions.