Soil microbes play a surprising role in corn hybrid vigour

Research shows ‘what’s driving heterosis’ — and it’s more than just the genetics in the seed

Tests in bags reflected the effects of heterosis when microbes were added.

The tiny organisms living in soil may have a greater effect than previously known on yield and crop resistance to pests and disease.

Researchers at North Carolina State University and the University of Kansas have shown that soil microbes — such as viruses, bacteria and fungi — play a role in heterosis or hybrid vigour, the superior performance of crossed plant lines, or hybrids, over inbred plant lines.

Research into hybrid vigour has generally highlighted the roles of genetic and abiotic environmental factors behind the phenomenon. Finding that the biotic soil environment impacts heterosis was a bit surprising.

“This work moves us toward a better understanding of what’s driving heterosis,” said Manuel Kleiner, an assistant professor of plant and microbial biology at North Carolina State and an author of a paper describing the research.

“Microbes are critical players in causing effects on corn plants. It’s not just temperature and soil type.”

The researchers experimented with two types of inbred corn plants and a hybrid of those two lines in laboratory and field tests in North Carolina and Kansas.

They started by growing the corn plants in sterile bags. Both types of plants grew similarly sized roots and shoots inside the bags. But when the researchers added a controlled set of microbes known to associate with corn roots in nature, hybrid lines grew more than inbred lines. Their roots and shoots weighed more, showing the expected effects of heterosis.

“This seemed to be the result of a negative microbial effect on inbred lines, rather than a helping effect on hybrids,” Kleiner said.

Similar heterosis-enhancing activity of microbes was observed in field tests in North Carolina in which hybrid and inbred lines were grown in untreated plots, plots treated with an antimicrobial chemical and in plots treated with both the antimicrobial chemical and a method of “cooking” the soil by sending ultra-hot steam into it.

Surprisingly, when a similar experiment was performed in Kansas, the opposite effect was observed. Treatments that reduced the microbial populations in the soil caused increased heterosis.

“We can now say that microbes will have effects on heterosis, but we can’t predict the direction of those effects,” Kleiner said.

The researchers plan to continue studying the effects of microbes on corn heterosis.

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