Submitted to: Molecular Breeding
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/30/2010
Publication Date: 9/4/2011
Citation: Burow, G.B., Franks, C., Burke, J.J., Xin, Z. 2011. Genetic dissection of early season cold tolerance in sorghum. Molecular Breeding. 28:391-402. Interpretive Summary: Sorghum like many other warm season cereal crops is vulnerable to cool soil and ambient air temperature at germination and seedling stages. An understanding of cold hardiness, especially early season cold tolerance is a key objective of the scientist involved in a number of sorghum improvement programs. The tagging and identification of chromosome regions and genes that control early season cold tolerance can immensely aid sorghum breeders in developing hardier lines and advance these lines faster from the experimental set-up to the farmers field. In this study, a Chinese landrace of sorghum referred to as Gaiagaoliang (a new source of cold tolerance) was crossed to an elite parent RTx430. High quality seeds of advance generation of offsprings were tested for the germinability under cool and optimal temperature in the laboratory and field emergence and vigor of seedlings at an early season planting time at two locations. Here the differences between 141 DNA markers were mapped. It was discovered that under laboratory conditions, two regions located in chromosome 1 and 2 were most likely to control germination at cold and optimal conditions. Note worthy was that a new region in chromosome 9 was found as likely to control field emergence. DNA markers were used as tag for these regions. Based on DNA tags it was revealed that offsprings with combined favorable alleles for cold germination and field emergence are now available and will serve as important starting point in efficient and effective introduction of early season cold tolerance in elite sorghum lines.
Technical Abstract: Early season cold tolerance during stand establishment at soil temperature of 15C (or below) is an important agronomic trait for warm season cereal crops such as sorghum. Sorghum (Sorghum bicolor L. Moench), generally lacks cold tolerance and is adversely affected by the stress during germination, emergence and early seedling growth. Notably, sources of early season cold tolerance are available in the diverse germplasm pool of sorghum. To better understand the genetics of early season cold tolerance in sorghum, mapping of quantitative trait loci (QTL) associated with early season cold tolerance traits and identification of markers for marker assisted selection (MAS) was carried out. A recombinant inbred population consisting of 171 F7-F8 recombinant inbred lines derived from the cross between RTx 430 (cold sensitive) and PI610727 (cold tolerant) was developed and a genetic map was constructed using microsattelites or simple sequence repeat (SSR) markers. The RILs were evaluated for cold and optimal temperature germinability, field emergence, and seedling vigor in two locations during early season planting. Several QTLs were detected for each trait. A QTL for cold germinability(Germ 12-2.1) coincided with optimalgerminability. Eight QTLs localized in chromosomes 1, 4, 7 and 9 were identified to be associated with improved field emergence in two locations. A novel QTL for field emergence (Fearlygerm-9.3) was found stable between two locations and could serve as source of markers for the trait selection. This study also demonstrated that PI 610727 could be a valuable parental source of cold tolerance for sorghum.