Leaf position, leaf age and plant age affect the expression of downy mildew resistance in Brassica oleracea

To complement existing control strategies, grape growers in humid climates desire cultivars with resistance to downy mildew caused by Plasmopara viticola. Numerous disease resistance screens of diverse Vitis germplasm have been conducted previously to identify downy mildew resistance; however, ratings of named cultivars were inconsistent and identities of resistant individuals in wild species were not typically provided. Inconsistencies among previous studies could be due to race-specific resistance. In the current study, controlled inoculations of two single isolates onto two leaf ages of 883 Vitis accessions were used and these results compared with natural infection in a fivefold replicated vineyard of 80 Vitis accessions in 2006 and 2007. Of the accessions rated in both assays, 16.2% were resistant to a single isolate but susceptible in the vineyard. Otherwise, there was good correlation of ratings between the field assay and the rating of older leaves (r = 0.62 to 0.71). Five accessions from Vitis cinerea, V. labrusca, and Vitis × champinii averaged zero severity in both vineyard years, yet some individuals of V. cinerea and V. labrusca were moderately or highly susceptible in the field. Similarly, although significant differences in mean severity separated V. vinifera, Vitis hybrid, V. riparia, and V. labrusca for single-isolate inoculations (from susceptible to resistant), notable intraspecies variation was identified for all well-represented species. Resistant individuals were identified in most species with the prominent exceptions of V. vinifera and V. acerifolia. Single-isolate, detached-leaf resistance ratings in 2006 corresponded well (94.6%) to 2007 ratings using a separate isolate collected from the same vineyard. Categorizing the ratings for this and previous studies, ratings infrequently corresponded among previous studies (31.9%) as well as between previous studies and the current single-isolate (34.9%) or vineyard (46.4%) ratings. These results highlight important factors for downy mildew resistance screens: leaf age, pathogen genotype, and host species and accession. The results further underscore the importance to breeders of uniform testing in multiple environments.

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Inheritance of downy mildew resistance and its relationship with biochemical traits in cauliflower ( Brassica oleracea L. var. botrytis )

Crop Protection ◽

10.1016/j.cropro.2017.12.024 ◽

2018 ◽

Vol 106 ◽

pp. 132-138 ◽

Cited By ~ 1

Author(s):

Arti Verma ◽

Yudhvir Singh

Keyword(s):

Brassica Oleracea ◽

Downy Mildew ◽

Downy Mildew Resistance ◽

Biochemical Traits ◽

Mildew Resistance ◽

Brassica Oleracea L

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Molecular Breeding Strategy and Challenges Towards Improvement of Downy Mildew Resistance in Cauliflower (Brassica oleracea var. botrytis L.)

Frontiers in Plant Science ◽

10.3389/fpls.2021.667757 ◽

2021 ◽

Vol 12 ◽

Author(s):

Ranjan K. Shaw ◽

Yusen Shen ◽

Zhenqing Zhao ◽

Xiaoguang Sheng ◽

Jiansheng Wang ◽

...

Keyword(s):

Brassica Oleracea ◽

Downy Mildew ◽

Molecular Breeding ◽

Draft Genome ◽

Full Potential ◽

Downy Mildew Resistance ◽

Resistance Qtls ◽

Mildew Resistance ◽

Resistant Cultivars ◽

Genomic Resources

Cauliflower (Brassica oleracea var. botrytis L.) is one of the important, nutritious and healthy vegetable crops grown and consumed worldwide. But its production is constrained by several destructive fungal diseases and most importantly, downy mildew leading to severe yield and quality losses. For sustainable cauliflower production, developing resistant varieties/hybrids with durable resistance against broad-spectrum of pathogens is the best strategy for a long term and reliable solution. Identification of novel resistant resources, knowledge of the genetics of resistance, mapping and cloning of resistance QTLs and identification of candidate genes would facilitate molecular breeding for disease resistance in cauliflower. Advent of next-generation sequencing technologies (NGS) and publishing of draft genome sequence of cauliflower has opened the flood gate for new possibilities to develop enormous amount of genomic resources leading to mapping and cloning of resistance QTLs. In cauliflower, several molecular breeding approaches such as QTL mapping, marker-assisted backcrossing, gene pyramiding have been carried out to develop new resistant cultivars. Marker-assisted selection (MAS) would be beneficial in improving the precision in the selection of improved cultivars against multiple pathogens. This comprehensive review emphasizes the fascinating recent advances made in the application of molecular breeding approach for resistance against an important pathogen; Downy Mildew (Hyaloperonospora parasitica) affecting cauliflower and Brassica oleracea crops and highlights the QTLs identified imparting resistance against this pathogen. We have also emphasized the critical research areas as future perspectives to bridge the gap between availability of genomic resources and its utility in identifying resistance genes/QTLs to breed downy mildew resistant cultivars. Additionally, we have also discussed the challenges and the way forward to realize the full potential of molecular breeding for downy mildew resistance by integrating marker technology with conventional breeding in the post-genomics era. All this information will undoubtedly provide new insights to the researchers in formulating future breeding strategies in cauliflower to develop durable resistant cultivars against the major pathogens in general and downy mildew in particular.

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ON THE WAY TO THE IDENTIFICATION OF A DOWNY MILDEW RESISTANCE GENE IN BRASSICA OLERACEA L.

Acta Horticulturae ◽

10.17660/actahortic.2013.1005.25 ◽

2013 ◽

pp. 233-237

Author(s):

J. Carlier ◽

C. Alabaça ◽

C. Rodrigues ◽

J. Leitão

Keyword(s):

Brassica Oleracea ◽

Downy Mildew ◽

Resistance Gene ◽

Downy Mildew Resistance ◽

Mildew Resistance ◽

Brassica Oleracea L ◽

The Way

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SCREENING TECHNIQUES FOR DOWNY MILDEW RESISTANCE IN GHERKIN CUCUMBERS

International Journal of Geomate ◽

10.21660/2017.40.2603 ◽

2017 ◽

Vol 13 (40) ◽

Author(s):

Piyavadee Charoenwattana

Keyword(s):

Downy Mildew ◽

Downy Mildew Resistance ◽

Mildew Resistance ◽

Screening Techniques

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High resolution mapping and candidate gene identification of downy mildew race 16 resistance in spinach

BMC Genomics ◽

10.1186/s12864-021-07788-8 ◽

2021 ◽

Vol 22 (1) ◽

Author(s):

Gehendra Bhattarai ◽

Wei Yang ◽

Ainong Shi ◽

Chunda Feng ◽

Braham Dhillon ◽

...

Keyword(s):

Candidate Genes ◽

Downy Mildew ◽

Association Analysis ◽

Spinacia Oleracea ◽

Genotyping By Sequencing ◽

Significant Snps ◽

Snp Markers ◽

Resistance Locus ◽

Downy Mildew Resistance ◽

Mildew Resistance

Abstract Background Downy mildew, the most devastating disease of spinach (Spinacia oleracea L.), is caused by the oomycete Peronospora effusa [=P. farinosa f. sp. spinaciae]. The P. effusa shows race specificities to the resistant host and comprises 19 reported races and many novel isolates. Sixteen new P. effusa races were identified during the past three decades, and the new pathogen races are continually overcoming the genetic resistances used in commercial cultivars. A spinach breeding population derived from the cross between cultivars Whale and Lazio was inoculated with P. effusa race 16 in an environment-controlled facility; disease response was recorded and genotyped using genotyping by sequencing (GBS). The main objective of this study was to identify resistance-associated single nucleotide polymorphism (SNP) markers from the cultivar Whale against the P. effusa race 16. Results Association analysis conducted using GBS markers identified six significant SNPs (S3_658,306, S3_692697, S3_1050601, S3_1227787, S3_1227802, S3_1231197). The downy mildew resistance locus from cultivar Whale was mapped to a 0.57 Mb region on chromosome 3, including four disease resistance candidate genes (Spo12736, Spo12784, Spo12908, and Spo12821) within 2.69–11.28 Kb of the peak SNP. Conclusions Genomewide association analysis approach was used to map the P. effusa race 16 resistance loci and identify associated SNP markers and the candidate genes. The results from this study could be valuable in understanding the genetic basis of downy mildew resistance, and the SNP marker will be useful in spinach breeding to select resistant lines.

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Mutants of downy mildew resistance in Lactuca sativa (lettuce).

Genetics ◽

10.1093/genetics/137.3.867 ◽

1994 ◽

Vol 137 (3) ◽

pp. 867-874

Author(s):

P A Okubara ◽

P A Anderson ◽

O E Ochoa ◽

R W Michelmore

Keyword(s):

Molecular Marker ◽

Downy Mildew ◽

Genomic Dna ◽

Spontaneous Mutation ◽

Multigene Families ◽

Downy Mildew Resistance ◽

Bremia Lactucae ◽

Wild Type ◽

Mildew Resistance ◽

Recessive Mutations

Abstract As part of our investigation of disease resistance in lettuce, we generated mutants that have lost resistance to Bremia lactucae, the casual fungus of downy mildew. Using a rapid and reliable screen, we identified 16 distinct mutants of Latuca sativa that have lost activity of one of four different downy mildew resistance genes (Dm). In all mutants, only a single Dm specificity was affected. Genetic analysis indicated that the lesions segregated as single, recessive mutations at the Dm loci. Dm3 was inactivated in nine of the mutants. One of five Dm 1 mutants was selected from a population of untreated seeds and therefore carried a spontaneous mutation. All other Dm1, Dm3, Dm5/8 and Dm7 mutants were derived from gamma- or fast neutron-irradiated seed. In two separate Dm 1 mutants and in each of the eight Dm3 mutants analyzed, at least one closely linked molecular marker was absent. Also, high molecular weight genomic DNA fragments that hybridized to a tightly linked molecular marker in wild type were either missing entirely or were truncated in two of the Dm3 mutants, providing additional evidence that deletions had occurred in these mutants. Absence of mutations at loci epistatic to the Dm genes suggested that such loci were either members of multigene families, were critical for plant survival, or encoded components of duplicated pathways for resistance; alternatively, the genes determining downy mildew resistance might be limited to the Dm loci.

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