DOI: 10.5061/dryad.bcc2fqzfc
title: Sorghum leaf blight phenotypes for two recombinant inbred line populations

description: Sorghum leaf blight and northern corn leaf blight, both caused by
 Exserohilum turcicum, are major diseases of sorghum and maize,
 respectively. Examining the genetic architecture of resistance in sorghum
 will lead to a better understanding of the relationship between resistance
 in sorghum and maize, which can ultimately enhance management options in
 both crops. In 2018 and 2019 we evaluated two sorghum recombinant inbred
 line (RIL) populations for resistance to E. turcicum. The BTx623 x IS3620C
 and BTx623 x SC155 populations consisted of 235 and 81 RILs, respectively.
 Resistance in both populations was moderately to highly heritable. We
 identified a total of six quantitative trait loci (QTL) across the two
 populations. Three QTL with small to moderate effect sizes were identified
 in the BTx623 x IS3620C population. Three QTL, including a large-effect
 QTL on chromosome three that explained 24% of the variation, were
 identified in the BTx623 x SC155 population. We compared the identified
 QTL with the position of northern corn leaf blight candidate genes and
 found eight candidate resistance gene orthologs that colocalize with the
 sorghum leaf blight QTL. There were also several nucleotide-binding
 leucine rich repeat encoding genes within the candidate intervals.
 Understanding host resistance in multiple species furthers our
 understanding of the Exserohilum turcicum pathosystem.
description: We evaluated two recombinant inbred line (RIL) populations. SC155
 is more resistant than BTx623 to <em>Colletotricum
 sublineolum</em>, the causal agent of anthracnose (Patil et al.
 2017). IS3620C has been noted to be genetically divergent from BTx623, and
 the two parents segregate for numerous agronomic traits (Burow et al.
 2011; Kong et al. 2018) IS3620C is a guinea line (Hart et al., 2001),
 while SC155 is included in the sorghum conversion panel (Patil et al.,
 2017). Both RIL populations were grown in the field as
 single row plots in the summer of 2018 and 2019 at the Crop Sciences
 Research and Education Center in Urbana, IL. Standard agronomic practices
 for central Illinois were employed. Populations were grown under irrigated
 conditions in 2018 and 2019 to favor disease development. For the BTx623 ×
 IS3620C population, 246 and 235 lines were evaluated in 2018 and 2019,
 respectively. For the BTx623 × SC155 population 86 and 81 lines were
 evaluated in 2018 and 2019, respectively. Differences in the number of
 lines evaluated in each year was due to seed availability. Experiments
 were designed as a randomized complete block design with two replications
 for both populations in 2018 and 2019 using the <em>agricolae
 </em>package (De Mendiburu, 2014) in the statistical software R,
 version 3.6.0 (R Core Team, 2021). The respective parents for each RIL
 population were included in each replication. Infested
 sorghum grains were used as the source of inoculum. Inoculum was prepared
 as described by X. Zhang et al. (2020) using the isolates 15st003,
 16st001, and 15st008. These strains were isolated from diseased sorghum
 leaves in Illinois in 2015 and 2016. The isolates were cultured in vitro
 for two weeks on lactose-casein hydrolysate agar with a 12-hour light/dark
 photoperiod. Once all plates had growth covering at least one-third of the
 surface, 1000 mL of soaked, autoclaved sorghum grain was cultured in a
 mushroom bag with agar pieces taken directly from the culture plates. Two
 agar plates with at least one third coverage of fungal mycelia were placed
 in each mushroom bag. Bags were cultured for 2-3 weeks at room temperature
 with a 12-hour light/dark photoperiod. After grains were fully infested
 and spores were visually confirmed using a dissecting microscope, the
 grain was dried and stored at room temperature until needed for
 inoculation. Each plant was inoculated with 1.3 g of the prepared inoculum
 in the whorl at the V5 growth stage, or 29 days after planting in 2018 and
 35 days after planting in 2019 (Abendroth et al., 2011). Each plot was evaluated for percent
 disease coverage using a 0-100 scale in 5% increments, with 0% indicating
 no disease and 100% indicating that all the leaf area of the plants in the
 plot were necrotic with disease (Poland & Nelson, 2011). Both
 populations were rated four times starting two weeks before the earliest
 maturing plants started flowering. Plots were rated every 7-14 days. The
 area under the disease progress curve (AUDPC) was calculated for each plot
 using the agricolae package (De Mendiburu, 2014). Days to anthesis (DTA),
 defined as the day when at least 50% of the plot had visible anthers
 emerged, was recorded for both populations in 2019. Using the
 AUDPC data for each population, mixed models were fitted in R/lme4 (Bates
 et al., 2015). Factors defined as follows: Y<sub>ijk</sub>
 represents the measured AUDPC value from the genotype <em>i
 </em>in replicate <em>j</em> in environment
 <em>k</em>; <em>μ</em> represents the grand mean;
 <em>G<sub>i</sub></em> represents the random
 effect of genotype <em>i</em>;
 <em>R<sub>j(k)</sub></em> represents the random
 effect of replication <em>i</em> nested in environment
 <em>k</em>; <em>E<sub>k</sub></em>
 represents the random effect of environment <em>k</em>;
 <em>GE<sub>ik</sub></em> represents the random
 effect of the interaction between genotype <em>i</em> and
 environment <em>k</em>; and ε<sub>ijk</sub>
 represents the random error associated with Y<sub>ijk</sub>
 were included in the model. A best linear unbiased predictor (BLUP) was
 calculated for each line using the ranef function. For the BTx623 × SC155
 population the genotype × environment interaction was included in the
 model, but it was not included in the model for the BTx623 × IS3620C RIL
 population. BLUPs were extracted from this model.