U.S. farmers have long hoped to extend sugarcane's growing range northward from the Gulf coast because it substantially increase the land available for sugar and (for as long as subsidies last) biofuels.

Several hybrid canes developed in the 1980s have proved hardy in cooler climes, surviving overwinter as far north as Booneville, Arkansas, but no one had tested whether
the offspring of crosses between sugarcane and a hardy, cold-tolerant grass, Miscanthus - "miscanes" - actually photosynthesize, and thus continue to grow, when the thermometer dips.

Researchers now report that two miscanes perform as well as the grass species Miscanthus x giganteus at 50 degrees Fahrenheit (10 degrees Celsius), staying green and converting carbon dioxide to plant matter at a steady rate. Although the rate of photosynthesis drops at 50 degrees, it doesn't stall out altogether, as it does in sugarcane. Unlike tropical sugarcane, Miscanthus x giganteus is just as productive in the cool spring and autumn as in the heat of summer. It sprouts earlier than corn in the spring, and its leaves stay green and active well into the autumn.

The researchers exposed the miscanes to 10 days of 10-degree C conditions in the laboratory, measuring the rate of photosynthesis all the while. When they raised temperatures again to 25 degrees (77 degrees F), photosynthesis rebounded in the miscanes similar to Miscanthus x giganteus x giganteus. This means that the gains in chill-tolerance did not blunt sugarcane's productivity - a happy finding, the researchers said.

Field studies confirmed the laboratory findings.

Modeling studies suggest that extending sugarcane's growing season by 30 days - allowing it to photosynthesize in cooler temperatures the way Miscanthus does - can boost sugarcane yield by as much as 25 percent in the U.S. 

"If we could get these plants to grow as far north as hardiness zone 8, that would be really great," said University of Illinois crop sciences professor Erik Sacks, who led the research with postdoctoral researcher Katarzyna Glowacka. "That's a huge amount of land, and some of it is not very productive currently."

The miscanes could be grown for sugar or as a productive biofuels crop on the least productive land in the American South, Sacks said.

"To avoid potential food vs. fuel concerns, we wouldn't put it in a place with highly productive agriculture, like the Mississippi Delta," he said.

Many years of work remain before chill-tolerant miscanes are available for production on a large scale, the researchers said. But the new findings establish that sugarcane can be made chill-tolerant without losses in productivity, they said.

 Published in Global Change Biology Bioenergy.