Heterosis or hybrid vigor refers to the superior phenotypes of hybrids relative to their parent inbred lines. Hybrid vigor was discovered in maize over a century ago and since then, comprise nearly all commercially grown grains. While quantitative genetic and molecular mechanisms have explained some heterotic patterns, the mechanism is still largely unknown. Previous work has shown that rhizosphere microbiomes differ between maize hybrid and inbred lines, and that microbiome features in hybrids are not intermediate to their parent lines. Here we show that heterosis of root biomass and germination in maize is dependent on the soil microbial community. To determine whether heterosis is apparent in highly controlled environments, two inbred lines (B73 and Mo17) and their hybrid (B73xMo17) were treated with either an uninoculated control or a synthetic community. In a subsequent experiment, the same lines were subjected to three treatments – farm soil slurry, autoclaved farm soil slurry, and sterile buffer control – to determine whether complex soil microbiomes also induce heterosis. Lastly, we conducted a field experiment to assess whether heterosis occurs in farm soil exposed to five soil treatments: steamed, fumigated with allyl isothiocyanate (AITC), steamed and fumigated with AITC, fumigated with chloropicrin, and untreated control.
Results/Conclusions
In the first growth chamber experiment, we observed that the inbred and hybrid plants did not show heterosis when grown under sterile conditions but did show heterotic patterns when grown with the synthetic bacterial community. In the second growth chamber experiment, the hybrid advantage was much more apparent in the live farm soil slurry than the autoclaved aliquot and sterile buffer control, which had similar biomasses for B73 and B73xMo17. A strong negative effect on germination for both inbred lines was also observed when treated with the live farm soil slurry but not for the hybrid. In the field experiment, heterosis of shoot biomass was not affected and rates of germination success were consistent among treatments. Together, our results show a negative effect of soil microbes on the germination and growth of B73 and Mo17 but not B73xMo17. These results demonstrate for the first time, to our knowledge, soil microbe’s role as ecological drivers of heterosis. Further investigation into the genetic mechanisms of microbe dependent heterosis can help us understand the evolution of plant-microbiome interactions and provide solutions to sustainable maize production.