Saccharum x Miscanthus intergeneric hybrids (miscanes) exhibit greater chilling tolerance of C4 photosynthesis and postchilling recovery than sugarcane (Saccharum spp. hybrids)

Although commercial sugarcane (Saccharum spp. hybrid) produces large biomass yields, its lack of cold tolerance limits its cultivation to the tropics and subtropics. In contrast, sugarcane's close relative, Miscanthus, tolerates low temperatures. We studied 18 miscane genotypes, derived from hybridizations between two genotypes of sugarcane and two genotypes of Miscanthus (one each of M. sinensis and M. sacchariflorus). In an initial greenhouse experiment on long-duration chilling stress (12-13 degrees C day/7-9 degrees C night), photosynthetic rates of the Miscanthus parents were significantly higher than the sugarcane parents after 7 days of chilling and were more than double by 14 days. The Miscanthus also retained more of their prechilling (22-25 degrees C day/13-15 degrees C night) photosynthetic rates (68%-72% 7 days, 64%-66% 14 days) than the sugarcanes (27% 7 days, 19%-20% 14 days). Seven of 18 miscanes exhibited higher photosynthetic rates than their sugarcane parents after 7 days of chilling, whereas after 14 days only four miscane genotypes had significantly higher photosynthetic rates than their sugarcane parents, but notably two of these did not differ from their highly tolerant Miscanthus parents. In a subsequent growth chamber experiment to evaluate short-duration chilling stress and postchilling recovery, three miscanes representing the range of responses observed in the greenhouse experiment were compared with their parents. After 4 days of chilling (12/7 degrees C day/night), the miscanes retained between 45% and 60% of their prechilling photosynthetic rate, with the best entry not significantly different from its Miscanthus parent (66%), and all three miscanes performed significantly better than the sugarcane parents (32%-33% for sugarcanes). After 7 days of postchilling recovery (26/18 degrees C day/night), the Miscanthus parents and two of the miscanes fully recovered their prechilling photosynthetic rates but the sugarcane parents only recovered 69%-73% of their prechilling rates. Thus, genes from Miscanthus can be used to improve chilling tolerance of sugarcane via introgression.