Marker-Assisted Gene Pyramiding and the Reliability of Using SNP Markers Located in the Recombination Suppressed Regions of Sunflower (Helianthus annuus L.).

Lili Qi,Guojia Ma

doi:10.3390/genes11010010

Abstract

Rust caused by the fungus Puccinia helianthi and downy mildew (DM) caused by the obligate pathogen Plasmopara halstedii are two of the most globally important sunflower diseases. Resistance to rust and DM is controlled by race-specific single dominant genes. The present study aimed at pyramiding rust resistance genes combined with a DM resistance gene, using molecular markers. Four rust resistant lines, HA-R3 (carrying the R4 gene), HA-R2 (R5), HA-R8 (R15), and RHA 397 (R13b), were each crossed with a common line, RHA 464, carrying a rust gene R12 and a DM gene PlArg. An additional cross was made between HA-R8 and RHA 397. Co-dominant simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers linked to the target genes were used to discriminate between homozygotes and heterozygotes in F2 populations. Five pyramids with different combinations of rust resistance genes were selected in the homozygous condition through marker-assisted selection, and three of them were combined with a DM resistance gene PlArg: R4/R12/PlArg, R5/R12/PlArg, R13b/R12/PlArg, R15/R12, and R13b/R15. The pyramiding lines with the stacking of two rust and one DM genes were resistant to all known races of North American sunflower rust and all known races of the pathogen causing DM, potentially providing multiple and durable resistance to both rust and DM. A cluster of 12 SNP markers spanning a region of 34.5 Mb on chromosome 1, which co-segregate with PlArg, were tested in four populations. Use of those markers, located in a recombination suppressed region in marker selection, is discussed.

Highlights

Sunflower (Helianthus annuus L.) is cultivated globally and is highly valued as a source of edible oil rich in lineoleic or oleic acids with a high vitamin E content
Five pyramids with different combinations of rust resistance genes were selected in the homozygous condition through marker-assisted selection, and three of them were combined with a downy mildew (DM) resistance gene
The pyramiding lines with the stacking of two rust and one DM genes were resistant to all known races of North American sunflower rust and all known races of the pathogen causing DM, potentially providing multiple and durable resistance to both rust and DM

Summary

Introduction

Sunflower (Helianthus annuus L.) is cultivated globally and is highly valued as a source of edible oil rich in lineoleic or oleic acids with a high vitamin E content. Sunflower crops can be infected by disease-causing bacterial, fungal, and viral pathogens, subsequently reducing yield and quality. De Toni are the two of the most important sunflower diseases. Rust caused by the fungus Puccinia helianthi Schwein. Downy mildew (DM) caused by the obligate pathogen Plasmopara halstedii (Farl.) Berl. Both are native to North America (NA) but have spread to nearly every sunflower growing region in the world; for review see [1,2]. Resistance to rust and DM is controlled by race-specific single dominant genes. There is a long history of the use of resistant varieties and hybrids to control rust and DM in sunflower production

Methods

Results

Conclusion