Recurrent selection for increased outcrossing rates in caudatum-race sorghum from Sudan
Final Report Abstract
Sorghum is a staple food for the majority of people living in the semi-arid areas of the Sudanian/Sahelian zone of Africa where most sorghum cultivars are specifically adapted to the respective climate. Under rain-fed conditions in Sudan, average grain yields are low and variable ranging from 0.5 to 0.8 t/ha. Farmer-preferred cultivars are genetically heterogeneous but display a low level of heterozygosity. The objective of this study were i) to increase the outcrossing rate in caudatum-race sorghum using recurrent selection (RS) and simple sequence repeat (SSR) markers as a tool for developing new sorghum populations with high heterozygosity, ii) to estimate population parameters determining progress from selection, and (iii) to provide sorghum materials with increased outcrossing rate to breeding programs in Sudan and ecologically similar regions of sub-Saharan Africa. One hundred parents, chosen for their early flowering and maturity, were intermated in an isolated crossing block. Progeny of this crossing block with a high level of heterozygosity were selected based on detection of polymorphism of SSR markers at seedling stage among populations. All established plants were sampled at the two-leaf stage for DNA extraction. Leaf tissue taken from 3200 plants (32 plants / accession) per cycle were genotyped using SSR markers and the 200 most polymorphic plants were selected as parents for the following RS cycle. This procedure was repeated for four subsequent selection cycles using five genomic markers in different combinations of duplex and triplex PCR. Molecular marker work was started in Germany at the University of Hohenheim and gradually transferred to the newly established laboratory of ARC in Wad Medani, Sudan. Molecular work and field experiments produced significant and publishable results. Genotyping data were used to estimate outcrossing rate in each cycle using the MLTR program. The outcrossing rate measured in progeny from a final field experiment increased after four cycles of recurrent selection from 15 to 35% from C0 to C4 population, respectively, and the observed heterozygosity increased from 7 to 26%. A significant positive effect of heterozygosity on grain yield and some other agronomic traits was observed at an unexpected magnitude. The immense increase of yield on a population basis can only partly be explained by heterosis. Additional forces such as improved individual (heterozygosity) and populational buffering (heterogeneity) and novel beneficial allelic combinations at numerous yield related genes which may have been formed through inter-mating within the genetically broad base-population, may have contributed to yield. Highly significant and positive correlation of heterozygosity with agronomic traits such as head diameter and head shape reflect the direct effect of heterozygosity. Large genetic variability and high heritability values together with high estimates of genetic advance indicate that further cycles of indirect recurrent selection could result in additional improvement of yield and yield related traits. Moreover, highly heterozygous RS populations showed improved drought tolerance. Finally, in only 4 cycles of RS improved genetic materials of sorghum with high potential for future breeding programs for marginal environments have been created. The project had a high capacity building component and helped to establish a functioning molecular marker laboratory, which has recently moved to Khartoum and is now the reference laboratory for biotechnology in Sudan.
Publications
- 2011. Marker-assisted recurrent selection for increased outcrossing rates in caudatum-race sorghum from Sudan. P 35-38 in: Book of abstracts, International CIMAC conference, University of Hohenheim, Stuttgart, 7-9 February 2011
Parzies, H.K., A.A. Abdallah, H.H. Geiger, and A.A. Ali
- 2011. Marker-assisted recurrent selection to increase outcrossing in sorghum caudatum-race from Sudan. PhD-thesis, Sudan Academy of Science, Agricultural Research Council
Abubaker Altahir Abdallah Mussa
