Introgression of an adult-plant powdery mildew resistance gene Pm4VL from Dasypyrum villosum chromosome 4V into bread wheat.

Powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) seriously threatens wheat production worldwide. It is imperative to identify novel resistance genes from wheat and its wild relatives to control this disease by host resistance. Dasypyrum villosum (2n = 2x = 14, VV) is a relative of wheat and harbors novel genes for resistance against multi-fungal diseases. In the present study, we developed a complete set of new wheat-D. villosum disomic introgression lines through genomic in situ hybridization (GISH), fluorescence in situ hybridization (FISH) and molecular markers analysis, including four disomic substitution lines (2n=42) containing respectively chromosomes 1V#6, 2V#6, 3V#6, and 6V#6, and four disomic addition lines (2n=44) containing respectively chromosomes 4V#6, 5V#6, 6V#6 and 7V#6. These lines were subsequently evaluated for their responses to a mixture Bgt isolates at both seedling and adult-plant stages. Results showed that introgression lines containing chromosomes 3V#6, 5V#6, and 6V#6 exhibited resistance at both seedling and adult-plant stages, whereas the chromosome 4V#6 disomic addition line NAU4V#6-1 exhibited a high level of adult plant resistance to powdery mildew. Moreover, two translocation lines were further developed from the progenies of NAU4V#6-1 and the Ph1b mutation line NAU0686-ph1b. They were T4DL·4V#6S whole-arm translocation line NAU4V#6-2 and T7DL·7DS-4V#6L small-fragment translocation line NAU4V#6-3. Powdery mildew tests of the two lines confirmed the presence of an adult-plant powdery mildew resistance gene, Pm4VL, located on the terminal segment of chromosome arm 4V#6L (FL 0.6-1.00). In comparison with the recurrent parent NAU0686 plants, the T7DL·7DS-4V#6L translocation line NAU4V#6-3 showed no obvious negative effect on yield-related traits, providing a new germplasm in breeding for resistance.

Transferring an Adult-Plant Stripe-Rust Resistance Gene Yr7VS from Chromosome 7V of Dasypyrum villosum (L.) to Bread Wheat.

Stripe rust (Puccinia striiformis West. f.sp. tritici, Pst) is a destructive disease that seriously threatens wheat production globally. Exploring novel resistance genes for use in wheat breeding is an urgent need, as continuous Pst evolution frequently leads to a breakdown of host resistance. Here, we identified a set of wheat-Dasypyrum villosum 01I139 (V#6) disomic introgression lines for the purpose of determining their responses to a mixture of Pst isolates CYR32, CYR33 and CYR34 at both seedling and adult-plant stages. The results showed that all introgression lines exhibited high susceptibility at the seedling stage, with infection-type (IT) scores in the range of 6-8, whereas, for chromosomes 5V#6 and 7V#6, disomic addition lines NAU5V#6-1 and NAU7V#6-1 displayed high resistance at the adult-plant stage, indicating that adult-plant resistance (APR) genes were located on them. Further, in order to transfer the stripe-rust resistance on chromosome 7V#6, four new wheat-D. villosum introgression lines were identified, by the use of molecular cytogenetic approaches, from the self-pollinated seeds of 7D and 7V#6, in double monosomic line NAU7V#6-2. Among them, NAU7V#6-3 and NAU7V#6-4 were t7V#6L and t7V#6S monosomic addition lines, and NAU7V#6-5 and NAU7V#6-6 were homozygous T7DS·7V#6L and T7DL·7V#6S whole-arm translocation lines. Stripe-rust tests and genetic analyses of chromosome 7V#6 introgression lines revealed a dominant APR gene designated as Yr7VS on the chromosome arm 7V#6S. Comparison with the homozygous T7DL·7V#6S translocation line and the recurrent parent NAU0686 showed no significant differences in yield-related traits. Thus, T7DL·7V#6S whole-arm translocation with the APR gene Yr7VS provided a valuable germplasm for breeding for resistance.

Introgression of an All-Stage and Broad-Spectrum Powdery Mildew Resistance Gene Pm3VS from Dasypyrum villosum Chromosome 3V into Wheat.

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a serious disease that threatens wheat production globally. It is imperative to explore novel resistance genes to control this disease by developing and planting resistant varieties. Here, we identified a wheat-Dasypyrum villosum 3V (3D) disomic substitution line, NAU3815 (2n = 42), with a high level of powdery mildew resistance at both the seedling and adult-plant stages. Subsequently, NAU3815 was used to generate recombination between chromosomes 3V and 3D. Through genomic in situ hybridization (GISH), fluorescence in situ hybridization (FISH), and 3VS- and 3VL-specific markers analysis, four introgression lines were developed from the selfing progenies of 3V and 3D double monosomic line NAU3816, which was derived from the F1 hybrids of NAU3815/NAU0686. There were t3VS (3D) ditelosomic substitution line NAU3817, t3VL (3D) ditelosomic substitution line NAU3818, homozygous T3DL·3VS translocation line NAU3819, and homozygous T3DS·3VL translocation line NAU3820. Powdery mildew tests of these lines confirmed the presence of an all-stage and broad-spectrum powdery mildew resistance gene, Pm3VS, located on chromosome arm 3VS. When compared with the recurrent parent NAU0686 plants, the T3DL·3VS translocation line NAU3819 showed no obvious negative effect on yield-related traits. However, the introduction of the T3DL·3VS translocated chromosome had a strong effect on reducing the flag-leaf length. Consequently, the T3DL·3VS translocation line NAU3819 provides a new germplasm in breeding for both resistance and plant architecture.

Wheat Pm55 alleles exhibit distinct interactions with an inhibitor to cause different powdery mildew resistance.

Powdery mildew poses a significant threat to wheat crops worldwide, emphasizing the need for durable disease control strategies. The wheat-Dasypyrum villosum T5AL·5 V#4 S and T5DL·5 V#4 S translocation lines carrying powdery mildew resistant gene Pm55 shows developmental-stage and tissue-specific resistance, whereas T5DL·5 V#5 S line carrying Pm5V confers resistance at all stages. Here, we clone Pm55 and Pm5V, and reveal that they are allelic and renamed as Pm55a and Pm55b, respectively. The two Pm55 alleles encode coiled-coil, nucleotide-binding site-leucine-rich repeat (CNL) proteins, conferring broad-spectrum resistance to powdery mildew. However, they interact differently with a linked inhibitor gene, SuPm55 to cause different resistance to wheat powdery mildew. Notably, Pm55 and SuPm55 encode unrelated CNL proteins, and the inactivation of SuPm55 significantly reduces plant fitness. Combining SuPm55/Pm55a and Pm55b in wheat does not result in allele suppression or yield penalty. Our results provide not only insights into the suppression of resistance in wheat, but also a strategy for breeding durable resistance.