Date Published: April 18, 2019
Publisher: Public Library of Science
Author(s): Nguyen Phuong, Gloria Afolayan, Hartmut Stützel, Ralf Uptmoor, Mohamed El-Soda, David A. Lightfoot.
Understanding the adaptation mechanisms of sorghum to drought and the underlying genetic architecture may help to improve its production in a wide range of environments. By crossing a high yielding parent (HYP) and a drought tolerant parent (DTP), we obtained 140 recombinant inbred lines (RILs), which were genotyped with 120 DArT and SSR markers covering 14 linkage groups (LGs). A subset of 100 RILs was evaluated three times in control and drought treatments to genetically dissect their response to water availability. Plants with early heading date (HD) in the drought treatment maintained yield (YLD) level by reducing seed number SN and increasing hundred seed weight (HSW). In contrast, early HD in the control treatment increased SN, HSW and YLD. In total, 133 significant QTL associated with the measured traits were detected in ten hotspot regions. Antagonistic, pleiotropic effects of a QTL cluster mapped on LG-6 may explain the observed trade-offs between SN and HSW: Alleles from DTP reduced SN and the alleles from HYP increased HSW under drought stress, but not in the control treatment. Our results illustrate the importance of considering genetic and environmental factors in QTL mapping to better understand plant responses to drought and to improve breeding programs.
Sorghum bicolor L. Moench. is native to arid and semi-arid tropical environments and a drought-tolerant cereal. In general, sorghum growing seasons in Sub-Saharan Africa are characterized by initial rainfalls with subsequent periods of drought. Sorghum plants with high vigor and fast growth rates during early developmental stages may be advantageous in regions affected by drought early in the season . A plant’s response to drought can be categorized into three adaptive strategies, i.e., drought escape (e.g by early flowering), drought tolerance (e.g. by improving water-use efficiency), and drought avoidance (e.g. by increasing water uptake and reducing water loss, [2–4]. Evaluating the natural variation of these responses by testing large numbers of genotypes in several environments improves the understanding of genotype by environment interactions (G×E) (, which in turn allows to select breeding lines with improved yield stability and helps to identify superior alleles across different environments . Dissecting the genetic components underlying G×E can be achieved via mapping quantitative trait loci (QTL) and their effects in different environments, i.e., by estimating QTL by environment interaction (Q×E) effects [7–9].
The population used here was genotyped with 120 DArT and SSR markers covering 14 LG and a total length of 1212 cM, which is comparable with the length of the sorghum consensus map, which had a size of 1355.4 cM . DArT markers were used because they are affordable and represent a powerful high-throughput marker system suitable for QTL mapping. However, we are aware that the use of additional SNPs would be necessary to provide equal genome coverage and to allow direct comparisons with recent or future studies, in which SNPs are used [16–18].
Understanding crop response to drought and the underlying QTL is essential to increase crop productivity under drought conditions which is the ultimate goal for breeding programs.