Highly effective mlo-based powdery mildew resistance in hexaploid wheat without pleiotropic effects

• Published in: Plant science (Limerick) 2023-10, Vol.335, p.111785-111785, Article 111785
• Main Authors: Ingvardsen, Christina R., Massange-Sánchez, Julio A., Borum, Finn, Füchtbauer, Winnie S., Bagge, Merethe, Knudsen, Søren, Gregersen, Per L.
• Format: Article
• Language: English
• Subjects: EMS mutagenesis; Hexaploid wheat; Mlo; Pleiotropic effects; Powdery mildew resistance; Triticum aestivum
• ISSN: 0168-9452; 1873-2259
• DOI: 10.1016/j.plantsci.2023.111785

Application of the mlo-based resistance in barley against powdery mildew attacks is a major success in crop breeding, since it confers durable disease resistance. Resistance caused by mutations in the Mlo gene seems to be ubiquitous across a range of species. This work addresses the introduction of mlo-based resistance into hexaploid wheat, which is complicated by the occurrence of three homoeologous genes: Mlo-A1, Mlo-B1 and Mlo-D1. EMS-generated mutant plants were screened for mutations in the three homoeologues. We selected and combined 6, 8, and 4 mutations, respectively, to obtain triple homozygous mlo mutant lines. Twenty-four mutant lines showed highly effective resistance towards attack by the powdery mildew pathogen under field conditions. All 18 mutations appeared to contribute to resistance; however, they had different effects on the occurrence of symptoms such as chlorotic and necrotic spots, which are pleiotropic to the mlo-based powdery mildew resistance. We conclude that to obtain highly effective powdery mildew resistance in wheat and to avoid detrimental pleiotropic effects, all three Mlo homoeologues should be mutated; however, at least one of the mutations should be of the weaker type in order to alleviate strong pleiotropic effects from the other mutations. •A range of different mutations in the three Mlo homoeologues in wheat can contribute to powdery mildew resistance.•Simultaneous mutations in all three Mlo homoeologues provide highly effective powdery mildew resistance in the field.•Strong mutations in all three Mlo homoeologues lead to severe pleiotropic effects, i.e. necrosis/chlorosis.•Weak mutations in one Mlo homoeologue can alleviate the pleiotropic effects from strong mutations in other homoeologues.•mlo mutations can be combined in wheat to obtain highly effective powdery mildew resistance without pleiotropic effects.