The Interaction Between Abiotic and Biotic Soil Factors Modulates Heterosis Expression in Maize

Heterosis, or hybrid vigor, refers to the phenotypic superiority of hybrids relative to their parental inbred lines. Recent work showed that manipulation of the soil microbial community consistently altered heterosis but the direction of the effect was dependent on microbiome composition, environment, or both. Abiotic factors such as temperature, water availability, and soil nutrients are known modifiers of heterosis expression; however, whether interactions between the soil microbial community and abiotic properties affect heterosis is largely unknown. To further understand how microbes influence heterosis, we characterized variation in maize heterosis when grown in soil inocula derived from historical maize farms or prairies. While we did not observe consistent differences in heterosis among plants grown in these inocula, our observations affirm that microbial effects on heterosis are likely specific to the local microbial community. The introduction of a nutrient amendment resulted in greater heterosis in the presence of an agricultural soil inoculum than in the presence of a prairie soil inoculum. In addition, the interaction between soil inoculum and nutrient treatment structured bacterial and fungal community composition in the root endosphere. Furthermore, root bacterial diversity was significantly higher under nutrient-limited conditions. These results suggest that the contributions of genotype by environment interactions to heterosis are dependent on microbial context. Further, they provide direct evidence for the interactive effect of the soil microbial community and abiotic environment on heterosis and suggest that consideration of the soil microbial community may be helpful for breeding hybrid maize varieties for optimized performance in diverse environmental contexts.