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RIPE: Powdery Mildew Resistance

Research in Plain English (RIPE)

Newly Identified Powdery Mildew Resistance Locus (REN11) on Chromosome 15 Confers Stable, Non Race Specific Resistance

Avinash Karn, Cheng Zou, Siraprapa Brooks, Jonathan Fresnedo-Ramirez, Franka Gabler, Qi Sun, David Ramming, Rachel Naegele, Craig Ledbetter and Lance Cadle-Davidson. (2021) Discovery of the REN11 Locus From Vitis aestivalis for Stable Resistance to Grapevine Powdery Mildew in a Family Segregating for Several Unstable and Tissue-Specific Quantitative Resistance Loci. Front. Plant Sci. 12:733899. doi: 10.3389/fpls.2021.733899

Summary by Michelle Podolec

The Takeaway

  • Grapevine Powdery Mildew (PM) is the most economically important foliar disease pathogen, with worldwide distribution.
     
  • Identifying broad-spectrum PM disease resistance loci is a goal of grape breeders and geneticists.
     
  • Of the 13 resistance loci known to breeders, most confer race-specific resistance (can be overcome, similar to single site fungicides); few confer broad-spectrum PM resistance.
     
  • This study, spanning 15 years, identified and confirmed the REN11 resistance locus.
     
  • REN11 provided strong PM resistance across leaf, rachis and berry tissues, and was stable and effective over years.
     
  • A set of DNA markers identified in this study can be used for marker-assisted selection for REN11.
     
  • These markers were used to find 28 additional breeding lines with REN11 resistance.

Background

Grape Powdery Mildew (PM) is caused by a genetically diverse pathogen (Erysiphe necator) that constantly evolves to overcome disease management strategies. Grape breeders seek to breed grapevines with broad-spectrum PM resistance, but this has been difficult as most resistance alleles are not effective against all PM isolates. This is known as race-specific resistance. Of the 13 PM resistance alleles currently known, few have the robust qualitative resistance grape breeders would desire. Further, most alleles show signs of being race-specific, which may lower their effectiveness to PM resistance under different use conditions.

A previous study hypothesized there were three independently assorting loci in the “Tamiami” population that conferred PM resistance. In this summary of 15 years of research, researchers tested that hypothesis further by exploring the reproducibility of those results across four different tissue types and in different environments.

Methods

Researchers in this project summarized data from 15 years of research, presenting information from 53 PM phenotypes (12 environments x four tissues, two greenhouse time points, a lab experiment, and two AUDPC tissues from a second family).

The researchers used Vitis hybrid c.v. Tamiami and prepared three crosses to validate the quantitative trait locus results. Progeny were grown at USDA ARS San Joaquin Valley Agricultural Sciences Center in Parlier, CA. Young vines were phenotyped for resistance to PM while being grown in the greenhouse, and also for their resistance in laboratory settings using PM inoculated samples and examining hyphal transects. Genotyping was performed using rhAmpSeq to determine haplotype variants across all vines in each family.  The four most frequent haplotypes within each family were identified. A genetic map was constructed for each grapevine family. The genotypes received quantitative trail loci (QTL) analysis to identify resistance loci. 

Researchers mapped the 19 grapevine chromosomes (Chr) and identified 12 QTL that were significant in different vineyard environments, greenhouse and lab experiments. Four QTL consistently were present in stems (Chr 8 and 9) and all four tissues tested (Chr 15), or all tissues except berries (Chr 6).

Researchers reviewed 20,651 vines previously fingerprinted with rhAmpSeq DNA markers for the desirable resistance alleles. They identified resistant progeny including those used in this study, 28 breeding lines, and four interspecific hybrid accessions located in the ARS repository at Winters, CA. This provides breeders with new sources of PM resistance.

Conclusions and Practical Considerations

Researchers discovered that REN11 from “Tamiami” and its resistant F1 offspring “B37-28” conferred moderate-to-strong, qualitative PM resistance. REN11 provided resistance across leaf, rachis and berry tissues, and was stable and effective over years. Resistance on stems was more complicated to determine, Ren11 and other loci on Chr 8 and 9 provide resistance in some environments. Chr 6 shows promise for additional foliar resistance to PM.

Michelle Podolec is extension support specialist with the statewide viticulture extension program, based at Cornell AgriTech in Geneva, NY.