Morphological characterization and identification of molecular markers for dwarfism genes in Sorghum bicolor L. [Moench]

[摘要] English: Sorghum is a grain crop with enormous potential in meeting the nutritional needs ofpeople in developing countries, as well as optimising current meat and poultryproduction in the rest of the world. Sorghum has been overlooked in recent years and isnot utilised to its full potential, especially in African countries. The conversion of exoticlines in terms of height and maturity holds great potential for the development ofimproved varieties. The genes controlling height or dwarfism (dw) have also been foundto enhance drought tolerance making it an important trait to be incorporated for sorghumimprovement in semi-arid areas. However, little information is available on the geneticand physiological basis of height.In this study, near-isogenic lines developed for different height classes werecharacterised (Chapter 2). Significant differences were observed in plant height,internode length and flag leaf length between different height classes as previouslyhypothesised. However, the current study also identified significant differences in flagleaf width, panicle weight and number of panicle branches between the different heightclasses, in contrast to previous reports comparing only two height classes. Furthermore,this is the first report that plant height is correlated to flag leaf length, flag leaf width,panicle weight, leaf sheath length and panicle length.The exogenous application of gibberellic acid (GA) did not result in a final heightincrease, as expected from previous reports (Chapter 3). However, it was observed thatGA application may affected the growth response in the different height classes. Thissuggests that dwarf genes probably do not affect gibberellic acid biosynthesis but rathermay act as a negative regulator in response to GA and that other genes, possibly thematurity genes determine the response to GA.This is the first report of using SSRs on near-isogenic lines for different height classes toidentify specific dwarfism genes (Chapter 4). Potential markers were identified for thedW1, dW2 and DW3 genes in sorghum. These markers also allowed the deduction ofgenotypes for the different height classes. Linkage group A was confirmed to containloci affecting plant height. These markers will facilitate sorghum breeding and reducethe time needed for line conversion.The AFLP technique was effective in identifying a total of 164 possible markers for thedifferent dwarfism genes (Chapter 5). Markers were identified for recessive anddominant dwarfism alleles at dW1, dW2 as well as dW3. Furthermore, the genetic distanceobserved between the different near-isogenic height classes and the parental linesindicate that a bias exists in the retention of an unexpectedly large donor segment,possibly introduced through the selection of height and maturity characteristics.Future research resulting from the present study includes further investigation of theinteraction between the dwarfism and maturity genes, as well as the verification of SSRand AFLP markers in genetic material with confirmed genotypes in order to incorporatethese markers into international breeding programmes. The use of these markers inconversion programmes will allow more cost effective and accelerated sorghumimprovement.

[发布机构] University of the Free State