Genome-wide association mapping for wheat blast resistance in CIMMYT's international screening nurseries evaluated in Bolivia and Bangladesh

Abstract

Wheat blast caused by the fungus Magnaporthe oryzae pathotype Triticum (MoT) is an emerging threat to wheat production. To identify genomic regions associated with blast resistance against MoT isolates in Bolivia and Bangladesh, we performed a large genome-wide association mapping study using 8607 observations on 1106 lines from the International Maize and Wheat Improvement Centre's International Bread Wheat Screening Nurseries (IBWSNs) and Semi-Arid Wheat Screening Nurseries (SAWSNs). We identified 36 significant markers on chromosomes 2AS, 3BL, 4AL and 7BL with consistent effects across panels or site-years, including 20 markers that were significant in all the 49 datasets and tagged the 2NS translocation from Aegilops ventricosa. The mean blast index of lines with and without the 2NS translocation was 2.7 ± 4.5 and 53.3 ± 15.9, respectively, that substantiates its strong effect on blast resistance. Furthermore, we fingerprinted a large panel of 4143 lines for the 2NS translocation that provided excellent insights into its frequency over years and indicated its presence in 94.1 and 93.7% of lines in the 2019 IBWSN and SAWSN, respectively. Overall, this study reinforces the effectiveness of the 2NS translocation for blast resistance and emphasizes the urgent need to identify novel non-2NS sources of blast resistance.

Figure 1

Population structure analysis in the 50 International Bread Wheat Screening Nursery (IBWSN) with 269 lines, 35 Semi-Arid Wheat Screening Nursery (SAWSN) with 265 lines, 51 IBWSN with 285 lines and 36 SAWSN with 287 lines.

Figure 2

Markers significantly associated with blast resistance in the 50 International Bread Wheat Screening Nursery (IBWSN). A Bonferroni α level of 0.20 was used to correct for multiple testing and the most significant marker in each chromosome is indicated.

Figure 3

Markers significantly associated with blast resistance in the 35 Semi-Arid Wheat Screening Nursery (SAWSN). A Bonferroni α level of 0.20 was used to correct for multiple testing and the most significant marker in each chromosome is indicated.

Figure 4

Markers significantly associated with blast resistance in the 51 International Bread Wheat Screening Nursery (IBWSN). A Bonferroni α level of 0.20 was used to correct for multiple testing and the most significant marker in each chromosome is indicated.

Figure 5

Markers significantly associated with blast resistance in the 36 Semi-Arid Wheat Screening Nursery (SAWSN). A Bonferroni α level of 0.20 was used to correct for multiple testing and the most significant marker in each chromosome is indicated.

Figure 6

Markers significantly associated with blast resistance in the combined panel comprising the 50 and 51 International Bread Wheat Screening nurseries, 35 and 36 Semi-Arid Wheat Screening Nurseries. A Bonferroni α level of 0.20 was used to correct for multiple testing and the most significant marker in each chromosome is indicated.

Figure 7

Genomic fingerprinting of blast associated markers and regions in 1106 lines from the the 50 and 51 International Bread Wheat Screening nurseries and 35 and 36 Semi-Arid Wheat Screening Nurseries. The green color indicates the favorable allele (allele with a decreasing effect on the blast index), the blue color indicates the unfavorable allele (allele with an increasing effect on the blast index), the magenta color indicates the heterozygote and the white color indicates missing data.

Figure 8

Box plots of marker alleles in 1106 lines plotted against the mean blast indices of the lines evaluated in Jashore 2019, Okinawa 2018 and 2019, Quirusillas 2018, 2019 and 2020. The favorable allele is the allele with a decreasing effect on the blast index and the unfavorable allele is the allele with an increasing effect on the blast index.