Phenotypic evaluation to stripe rust and leaf rust
The leaf rust FDS of parent L224-3 was less than 10% and showed good resistance to leaf and stripe rust. The FDS of Zhengzhou 5389 was 100% across four environments, while the mean stripe rust FDS of Zhengzhou 5389 ranged from 50 to 100% in all environments (Fig. 1 and Fig. 2). The MDS in eight environments were significantly correlated with Pearson correlation coefficients (r) ranging from 0.215 to 0.910 (P < 0.01) (Table 1).
Table 1
Pearson correlation coefficients (r) for two-way comparisons of stripe rust and leaf rust responses in all environments.
Environmena | YR2017BD | YR2016BD | YR2017MY | YR2016MY | LR2017ZK | LR2016ZK | LR2017BD |
YR2016BD | 0.672** | | | | | | |
YR2017MY | 0.581** | 0.490** | | | | | |
YR2016MY | 0.487** | 0.557** | 0.670** | | | | |
LR2017ZK | 0.363** | 0.215** | 0.383** | 0.244** | | | |
LR2016 ZK | 0.410** | 0.361** | 0.341** | 0.342** | 0.636** | | |
LR2017BD | 0.349** | 0.224** | 0.357** | 0.209** | 0.910** | 0.647** | |
LR2016BD | 0.349** | 0.303** | 0.395** | 0.386** | 0.673** | 0.837** | 0.649** |
a Stripe rust severities were evaluated at Mianyang (MY) (2016 and 2017) and Baoding (BD) (2016 and 2017) and leaf rust severities were evaluated at Baoding (2016 and 2017) and Zhoukou (ZK) (2016 and 2017). |
** P < 0.01. |
Linkage map construction
After removing SNPs with monomorphism, markers with missing rate > 10%, and sites with distortion ratios (P < 1E− 5), 2,941 polymorphic markers were retained, 96 for the 1A chromosome, 213 for the 2A chromosome, 177 for the 2B chromosome, 192 for the 3A chromosome, 1882 for the 4B chromosome, 172 for the 6D chromosome, and 209 for the 7B chromosome (Fig. 3). A total of 1142 pairs of molecular markers (SSR primers) were screened to detect polymorphism between resistant parent L224-3 and susceptible parent Zhengzhou 5389. The results showed that 356 pairs of SSR primers showed polymorphism in the two parents before being analyzed for polymorphism in small populations. Finally, 19 pairs of molecular markers linked to potentially resistant genes were screened to detect the whole RIL population and construct a genetic linkage map for further QTL analysis. The 19 pairs of molecular markers were: Xbarc148, Xwmc312, Xgwm135, Xwmc183, Xwmc407, Xbarc124, Xbarc212, Lr37, Xgwm495, Xgwm165, Xgwm513, Xgwm251, Xgwm310, Xwmc47, Xwmc125, XGwm6, Xwmc517, Xwmc723, and Xgwm302.
QTL analysis for leaf and stripe rust resistance
Four resistant QTL were detected on chromosomes 1A, 2A, 4B and 7B, respectively, in the L224-3/Zhengzhou 5389 population (Table 2, Fig. 4). QLr.hbau-1A/QYr.hbau-1A, QLr.hbau-2A/QYr.hbau-2A, and QLr.hbau-4B/QYr.hbau-4B conferred resistance to both rusts, while QYr.hbau-7B conferred APR to stripe rust only.
Table 2
QTL for final disease severity to stripe rust and leaf rust in 166 RILs from the L224-3/Zhengzhou 5389 population.
Environmenta | QTLb | Chromosome | Interval | LOD scorec | Additived | R(%)e |
2016 BD Yr | QYr.hbau-1A | 1A | Xbarc148-Xwmc312 | 5.78 | 0.86 | 2.50 |
| QYr.hbau-2A | 2A | Xwmc407-Lr37 | 5.26 | -0.25 | 3.54 |
| QYr.hbau-4B | 4B | Xgwm251-Xwmc310 | 3.66 | -4.36 | 9.60 |
| QYr.hbau-7B | 7B | Xwmc517-Xwmc723 | 6.43 | -1.82 | 3.62 |
2016 MY Yr | QYr.hbau-4B | 4B | Xgwm251-Xwmc310 | 3.45 | -7.04 | 6.90 |
2017 BD Yr | QYr.hbau-2A | 2A | Xwmc407-Lr37 | 34.94 | -2.91 | 6.30 |
| QYr.hbau-4B | 4B | Xgwm251-Xwmc310 | 8.01 | -2.68 | 8.07 |
| QYr.hbau-7B | 7B | Xwmc517-Xwmc723 | 5.79 | -1.12 | 5.79 |
2017 MY Yr | QYr.hbau-1A | 1A | Xbarc148-Xwmc312 | 3.34 | 0.54 | 2.87 |
| QYr.hbau-2A | 2A | Xwmc407-Lr37 | 10.82 | -12.17 | 25.57 |
| QYr.hbau-4B | 4B | Xgwm251-Xwmc310 | 4.36 | -7.28 | 10.71 |
| QYr.hbau-7B | 7B | Xwmc517-Xwmc723 | 2.70 | -3.24 | 2.70 |
2016 BD Lr | QLr.hbau-2A | 2A | Xwmc407- Lr37 | 43.05 | -30.05 | 54.07 |
| QLr.hbau-4B | 4B | Xgwm251-Xwmc310 | 3.37 | -9.67 | 8.78 |
2016 ZK Lr | QLr.hbau-1A | 1A | Xbarc148-Xwmc312 | 2.77 | 0.41 | 2.26 |
| QLr.hbau-2A | 2A | Xwmc407-Xbarc124 | 10.48 | -7.27 | 27.30 |
2017 BD Lr | QLr.hbau-2A | 2A | Xwmc407- Lr37 | 16.22 | -15.55 | 39.16 |
2017 ZK Lr | QLr.hbau-2A | 2A | Xwmc407- Lr37 | 19.50 | -15.87 | 37.51 |
a Stripe rust severities were evaluated at Mianyang (MY) (2016 and 2017) and Baoding (BD) (2016 and 2017) and leaf rust severities were evaluated at Baoding (2016 and 2017) and Zhoukou (ZK) (2016 and 2017). |
b QTL that overlap in one-log support confidence intervals were assigned the same symbol |
c Logarithm of odds (LOD) score |
d Additive effect of the resistance allele |
e Percentage of phenotypic variance explained by individual QTL |
QLr.hbau-1A/QYr.hbau-1A, the first QTL, was within the marker interval Xbarc148-Xwmc312. QLr.hbau-1A was only detected in Zhoukou 2016, and explained 2.26% of the phenotypic variances in leaf rust. QYr.hbau-1A was detected in Baoding 2016 and Mianyang 2017, explaining 2.5% and 2.87% of the phenotypic variances in stripe rust, respectively (Table 2, Fig. 4).
The second QTL, QLr.hbau-2A/QYr.hbau-2A, was identified as Lr37/Yr17 based on marker detection. On 2AS two QTL loci, QLr.hbau-2A.1/QYr.hbau-2A.1 and QLr.hbau-2A.2/QYr.hbau-2A.2, were detected, one of the QTL was within the Xwmc407-Xbarc124 marker interval and the other locus was within the Xbarc212-Lr37 marker interval. The genetic distance between the two QTL loci was only 3.3 cM, so the two QTL detected on 2A should be provided by the same gene Lr37/Yr17. Lr37/Yr17 was stably detected in all environments assessed for leaf rust and explained 37.51–54.07% of the phenotypic variances. For stripe rust, QYr.hbau-2A was detected in three environments (except for Mianyang 2016), and explained 3.54–25.5% of the phenotypic variances (Table 2, Fig. 4).
The third QTL, QLr.hbau-4B/QYr.hbau-4B, is flanked by markers Xgwm251-Xwmc310. QLr.hbau-4B was only detected in Baoding 2016 for leaf rust, explaining 3.37% of the phenotypic variances. QYr.hbau-4B was stably detected in all environments for stripe rust evaluation and explained 6.9–10.71% of the phenotypic variances (Table 2, Fig. 4).
The last QTL, QYr.hbau-7B, within the marker interval Xwmc517-Xwmc723 was detected in three stripe rust environments (except for Mianyang 2016), and explained 2.7–5.79% of the phenotypic variances (Table 2, Fig. 4).