Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2005
Publication Date: 4/25/2006
Citation: Franks, C.D., Burow, G.B., Burke, J.J. 2006. A comparison of US and Chinese sorghum germplasm for early season cold tolerance. Crop Science. 46:1371-1376. Interpretive Summary: Grain sorghum is an important crop in the Southern Great Plains, but since it is of tropical origin, the dates and locations in which it can be grown are limited due to cool soil temperatures early in the planting season. Developing grain sorghum lines which can tolerate these low temperatures would be of significant benefit to growers within this region. It has previously been reported that sorghum from certain regions in China has a distinct genetic advantage in terms of its ability to germinate and grow under cool conditions. In this study, we compared a set of ten of these Chinese lines, ten U.S. hybrids, and ten U.S. parental lines commonly used in making hybrids, for germination and seedling cold tolerance. We evaluated all 30 of these lines for germination across a range of temperatures in the laboratory, for seedling growth under cool conditions in a growth chamber, and for emergence and seedling growth in an early spring field trial. It was found that the Chinese lines germinated and emerged faster, and at lower temperatures, than either class of U.S. material. Most U.S. hybrids quickly overcame this disadvantage by means of their vigorous seedling growth, but the Chinese lines remained superior to the U.S. parental lines throughout the tests. The results observed in the growth chamber corresponded well with those observed in the field trial. We conclude from these findings that 1) The Chinese lines would be a very good source of favorable genes for cold tolerance, especially for fast germination and stand establishment, and 2) The growth chamber is a suitable tool for simulating field conditions in cold tolerance studies.
Technical Abstract: Early season cold tolerance in grain sorghum [Sorghum bicolor (L.) Moench] is a desirable trait for extending its production range and minimizing risks associated with early spring plantings. This study was conducted to evaluate a set of Chinese germplasm of the working group Nervosum-Kaoliang for early season cold tolerance, both in germination and early season vigor. Ten Chinese accessions were compared with ten U.S. inbred parental lines and ten U.S. commercial hybrids for a range of cold tolerance traits under laboratory, growth chamber, and field settings. For germination under suboptimal temperatures, Kaoliangs were superior to both the inbred and hybrid classes, which were essentially identical in their response to germination-phase cold stress. This superiority manifested itself in the field in rate of emergence, as the Kaoliangs were substantially faster in emergence than the other two germplasm classes. In the growth chamber assays, Kaoliangs were not statistically different than U. S. hybrids for most traits measured at either of the two temperature treatments (12'C and 24'C), with the exception of shoot length, for which the Chinese germplasm was higher. At the cooler temperature, Kaoliangs were statistically greater than U. S. inbreds for only fresh shoot weight; when tested at the warmer temperature, Kaoliangs excelled for dry root weight, fresh and dry shoot weights, and fresh and dry whole plant weights, relative to the U.S. inbred class. With respect to variables measured in the field, the hybrids were statistically superior to Kaoliangs for total plot weight and final stand counts, and Kaoliangs were likewise superior to U. S. inbreds for both of these traits. For rate of field emergence, the Chinese germplasm showed a statistically significant superiority to both U.S. germplasm classes, and hybrids were significantly faster emerging than U.S. inbreds. It appears that Chinese accessions from this working group would serve as a source of favorable genes primarily for tolerance to low temperatures during the germination and emergence phase of growth in the breeding of cold tolerance sorghum lines. Significant correlations among variables related to early season cold tolerance measured in both the field and growth chamber indicated that growth chamber studies would be suitable for preliminary screening of sorghum germplasm for cold tolerance.