19 research outputs found
Using a limited mapping strategy to identify major QTLs for resistance to grapevine powdery mildew (Erysiphe necator) and their use in marker-assisted breeding
A limited genetic mapping strategy based on simple sequence repeat (SSR) marker data was used with five grape populations segregating for powdery mildew (Erysiphe necator) resistance in an effort to develop genetic markers from multiple sources and enable the pyramiding of resistance loci. Three populations derived their resistance from Muscadinia rotundifolia âMagnoliaâ. The first population (06708) had 97 progeny and was screened with 137 SSR markers from seven chromosomes (4, 7, 9, 12, 13, 15, and 18) that have been reported to be associated with powdery or downy mildew resistance. A genetic map was constructed using the pseudo-testcross strategy and QTL analysis was carried out. Only markers from chromosome 13 and 18 were mapped in the second (04327) and third (06712) populations, which had 47 and 80 progeny, respectively. Significant QTLs for powdery mildew resistance with overlapping genomic regions were identified for different tissue types (leaf, stem, rachis, and berry) on chromosome 18, which distinguishes the resistance in âMagnoliaâ from that present in other accessions of M. rotundifolia and controlled by the Run1 gene on chromosome 12. The âMagnoliaâ resistance locus was termed as Run2.1. Powdery mildew resistance was also mapped in a fourth population (08391), which had 255 progeny and resistance from M. rotundifolia âTrayshedâ. A locus accounting for 50% of the phenotypic variation mapped to chromosome 18 and was named Run2.2. This locus overlapped the region found in the âMagnoliaâ-based populations, but the allele sizes of the flanking markers were different. âTrayshedâ and âMagnoliaâ shared at least one allele for 68% of the tested markers, but alleles of the other 32% of the markers were not shared indicating that the two M. rotundifolia selections were very different. The last population, 08306 with 42 progeny, derived its resistance from a selection Vitis romanetii C166-043. Genetic mapping discovered a major powdery mildew resistance locus termed Ren4 on chromosome 18, which explained 70% of the phenotypic variation in the same region of chromosome 18 found in the two M. rotundifolia resistant accessions. The mapping results indicate that powdery mildew resistance genes from different backgrounds reside on chromosome 18, and that genetic markers can be used as a powerful tool to pyramid these loci and other powdery mildew resistance loci into a single line
Downy mildew resistance evaluation in 28 grapevine hybrids promising for breeding programs in Trentino region (Italy)
Downy mildew is a major grapevine disease
caused by the biotrophic oomycete, Plasmopara
viticola. Numerous disease resistance studies of diverse
Vitis germplasm have been previously carried out to
identify downy mildew resistance sources; however,
ratings were mainly reported using leaf disc in vitro
testing and foliage field assessment, or upon leaf and
cluster field evaluations. In the current study, 28 grapevine
hybrid cultivars were screened using leaf disc bioassay,
for disease resistance characterization of both
existing and wild-collected materials. 16 hybrids were
identified as highly resistant or resistant, and will serve
as relevant resistance donors in future pre-breeding and
breeding programs. All grapevine hybrids were evaluated
for foliar and cluster downy mildew resistance in an
untreated field trial over three successive years. This
study showed that the leaf disc bioassay provided some
information on the resistance level of the genotypes
under scrutiny, but it was a weak predictor of their
resistance level under field conditions on leaves and
even more on bunches. These findings are relevant to
future applications in both traditional and marker-assisted
breeding programs which promote sustainable
viticulture