<p></p><p>Sorghum (<i>Sorghum bicolor) </i>is a well-known
agronomic crop of global importance. The demand for sorghum as a food crop
makes it the fifth most important cereal in the world. The grain of sorghum is
utilized for food and feed, whereas the sorghum biomass may have many other
uses such as for fodder, bioenergy or even for construction. Globally, sorghum
is consumed as a food crop and used for home construction primarily in the
developing world. The grain and biomass
yield of sorghum is drastically reduced by the parasitic plant <i>Striga hermonthica </i>which is endemic to
Sub-Saharan Africa. To date, only one sorghum gene, <i>LGS1</i>, has been characterized as a genetic mechanism that reduces <i>S. hermonthica</i> parasitism by altering
the strigolactone composition of the host root exudates which results in a
reduction of the parasites ability to germinate. To establish more durable
resistance additional genetic variation needs to be identified that reduces the
<i>S. hermonthica </i>parasitism in sorghum,
but also reduces the parasitic weed seed bank by promoting suicidal
germination. To that end, the PP37 multi-parent advanced generation inter-cross
(MAGIC) population was developed, originally as a recurrent selection
population that was developed to recombine sorghum accessions with different
putative resistance mechanisms to <i>S.
hermonthica. </i>Whole genome sequences were developed for approximately 1,006
individuals of the PP37 MAGIC population. The population was phenotyped for <i>S. hermonthica </i>resistance during the
2016 and 2017 growing season in Northwestern Ethiopia. There was significant
spatial variation in the <i>S. hermonthica </i>natural
infestations that were partially attenuated for with artificial inoculation.
The data was used to conduct a genome-wide association study that detected
several subthreshold peaks, including the previously mapped <i>LGS1. </i>The highly quantitative nature of <i>S. hermonthica </i>resistance confounded
with the complex spatial variation in the parasite infestations across a given
location make it difficult to detect highly heritable variation across years
and environments. </p>
<p> In
addition to <i>S. hermonthica </i>resistance,
the plant architecture of the PP37 MAGIC was also assessed at a location in
Northwestern Ethiopia that is free of the parasite, as it significantly reduces
plant height. To asses plant architecture the total plant height, the height of
the panicle base, flag leaf height, and pre-flag leaf height were collected
using a relatively high-throughput barcoded measurement system. Sorghum head
exertion and panicle length were derived from this data. The actual measures of
plant architecture and the derived traits were used to conduct a genome-wide
association study. The high heritability of this trait demonstrated the
statistical power of the PP37 mapping population. Highly significant peaks were
detected that resolved the <i>dwarf3</i>
locus and an uncharacterized qHT7.1 that had only been previously resolved
using a recombinant inbred line population. Furthermore, a novel significant
locus was associated with exertion on chromosome 1. The random mating that was
utilized to develop the PP37 MAGIC has broken the population structure that
when present can hinder our ability associate regions of the genome to a given
phenotype. As a result, novel candidate gene lists have been developed as an
outcome of this research that refined the potential genes that need to be
explored to validate qHT7.1 and the novel association on chromosome 1. </p>
<p>This research
demonstrated the power of MAGIC populations in determining the genomic regions
that influence complex phenotypes, that facilitates future work in sorghum
genetic improvement through plant breeding.
This research however also demonstrates a large international research
effort. The nuisances and lessons learned while conducting this international research
project are also discussed to help facilitate and guide similar research
projects in the future. The broader impacts of this research on the society at
large are also discussed, to highlight the unique potential broader impacts of
international research in the plant sciences. The broader impacts of this
research include germplasm development and extensive human capacity building in
plant breeding genetics for developing country students and aspiring
scientists. Overall this research attempts to serve as a model for highlighting
the interdisciplinary nature and complexity of conducting international plant
science research, while also making significant strides in improving our understanding
the genetic architecture of quantitative traits of agronomic importance in
sorghum.</p><br><p></p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/10286864 |
| Date | 20 November 2019 |
| Creators | Megan E Khangura (7847480) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/A_Genome-wide_Association_Study_of_the_Quantitative_Resistance_to_i_Striga_hermonthica_i_and_Plant_Architecture_of_i_Sorghum_bicolor_i_in_Northwestern_Ethiopia/10286864 |
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