Phenotypic Variation for Downy Mildew Resistance among Inbred Broccoli

Downy mildew, caused by Peronospora parasitica (Pers. Fr.) Fr., is one of the most economically important diseases of broccoli (Brassica oleracea L. Italica group). Previous studies have shown that resistance to downy mildew in broccoli is dependent on plant age with seedling resistance being independent of mature-plant resistance. The objectives of this study were to: 1) determine if valid evaluations for downy mildew resistance can be conducted at both the cotyledon and the three to four true-leaf stages on the same plants of a given broccoli entry; 2) determine if doubled-haploid (DH) lines derived from the resistant hybrid `Everest' also exhibit resistance to downy mildew and if so, characterize the resistance phenotype(s) in these lines; and 3) determine if identified resistant DH lines exhibit resistance to isolates of P. parasitica acquired from different geographic regions of the United States. Twenty-three DH broccoli inbreds and two commercial hybrids were evaluated for reaction at different developmental stages to infection by P. parasitica in a controlled environment. Results showed that broccoli plants can be evaluated for downy mildew resistance in a two-stage process. Inoculation at the cotyledon stage did not offer any cross-protection or otherwise influence the expression of reaction phenotype (RP) when the same plants were subsequently inoculated at the three to four true-leaf stage. Three different RPs to infection by P. parasitica were identified in DH inbreds. These were: 1) susceptibility at both the cotyledon stage and the true-leaf stage; 2) resistance at both the cotyledon and true-leaf stage; and 3) susceptibility at the cotyledon stage but resistance at the true-leaf stage. There was no effect of two pathogenic isolates from different geographic regions on RP of DH broccoli inbreds. Selection of plant resistance to downy mildew at the cotyledon stage will effectively identify plants with high levels of resistance at subsequent developmental stages.

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Inheritance of True Leaf Stage Downy Mildew Resistance in Broccoli

Journal of the American Society for Horticultural Science ◽

10.21273/jashs.126.6.727 ◽

2001 ◽

Vol 126 (6) ◽

pp. 727-729 ◽

Cited By ~ 11

Author(s):

Min Wang ◽

Mark W. Farnham ◽

Claude E. Thomas

Keyword(s):

Downy Mildew ◽

Control Method ◽

Recurrent Parent ◽

Downy Mildew Resistance ◽

Resistant Parent ◽

Dh Population ◽

Mildew Resistance ◽

Leaf Stage ◽

True Leaf ◽

High Level

Downy mildew, incited by the biotrophic fungal parasite, Peronospora parasitica (Pers. Fr.) Fr., is one of the most destructive diseases of broccoli (Brassica oleracea L., Italica Group) and other related crop species throughout the world. Cultivation of resistant cultivars is the most desirable control method because it provides a practical, long-term, and environmentally benign means of limiting damage from this disease. The commercial hybrid cultivar, Everest, has been shown previously to contain a high level of downy mildew resistance. Doubled-haploid (DH) lines developed from that hybrid were also shown to exhibit a similar, high level of resistance at the three- to four-leaf stage. To determine the mode of inheritance of this true leaf resistance, the resistant DH line was crossed to a susceptible line (derived from `Marathon') to produce an F1 hybrid. Subsequently, F2 and backcross (BC) populations were developed from the hybrid. In addition, a DH population of ≈100 lines was developed from the same F1 used to create the F2 and BC. All populations were evaluated for response to artificial inoculation with P. parasitica at the three- to four-leaf stage. F1 plants were resistant like the resistant parent and F2 populations segregated approximately nine resistant to seven susceptible. Using the resistant parent as recurrent parent, BC populations contained all resistant plants, while the BC to the susceptible parent fit a 1 resistant: 3 susceptible segregation ratio. These results can be explained by a model with two complementary dominant genes. This model was confirmed by the DH population that segregated ≈1:3, resistant to susceptible. Due to the dominant nature of this resistance, controlling genes should be easily incorporated into F1 hybrids and used commercially to prevent downy mildew.

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Genetic and histological characterization of downy mildew resistance at the cotyledon stage in Raphanus sativus L.

Euphytica ◽

10.1007/s10681-018-2289-x ◽

2018 ◽

Vol 214 (11) ◽

Cited By ~ 1

Author(s):

Paula S. Coelho ◽

António A. Monteiro

Keyword(s):

Downy Mildew ◽

Raphanus Sativus ◽

Downy Mildew Resistance ◽

Mildew Resistance ◽

Cotyledon Stage ◽

Raphanus Sativus L

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Construction of a sequence-based bin map and mapping of QTLs for downy mildew resistance at four developmental stages in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

Molecular Breeding ◽

10.1007/s11032-016-0467-x ◽

2016 ◽

Vol 36 (4) ◽

Cited By ~ 14

Author(s):

Shuancang Yu ◽

Tongbing Su ◽

Shenghua Zhi ◽

Fenglan Zhang ◽

Weihong Wang ◽

...

Keyword(s):

Downy Mildew ◽

Brassica Rapa ◽

Chinese Cabbage ◽

Developmental Stages ◽

Downy Mildew Resistance ◽

Mildew Resistance ◽

Bin Map

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Inheritance of downy mildew resistance at different developmental stages in Chinese cabbage via the leaf disk test

Horticulture Environment and Biotechnology ◽

10.1007/s13580-012-0057-8 ◽

2012 ◽

Vol 53 (5) ◽

pp. 397-403 ◽

Cited By ~ 7

Author(s):

Shengju Zhang ◽

Shuancang Yu ◽

Fenglan Zhang ◽

Longting Si ◽

Yangjun Yu ◽

...

Keyword(s):

Downy Mildew ◽

Chinese Cabbage ◽

Developmental Stages ◽

Leaf Disk ◽

Downy Mildew Resistance ◽

Mildew Resistance ◽

Disk Test ◽

Leaf Disk Test

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033 Characterization of Downy Mildew Resistance in USDA Broccoli Inbreds

HortScience ◽

10.21273/hortsci.34.3.446e ◽

1999 ◽

Vol 34 (3) ◽

pp. 446E-447

Author(s):

Min Wang ◽

Mark W. Farnham

Keyword(s):

Downy Mildew ◽

Screening Tests ◽

Downy Mildew Resistance ◽

Block Designs ◽

Peronospora Parasitica ◽

Seedling Resistance ◽

Mature Plant Resistance ◽

Leaf Stage ◽

Cotyledon Stage

Downy mildew, caused by Peronospora parasitica (Pers. ex Fr.), is one of the most economically important diseases in broccoli (Brassica oleracea L. Italica group). Previous studies reported that resistance to downy mildew in broccoli depends on plant age and that seedling resistance appears to be independent of mature-plant resistance. The objectives of our studies were to evaluate resistance and susceptibility of USDA broccoli inbreds to downy mildew and to investigate the interaction between the host and pathogen at two plant stages with single or double inoculation. Multiple screening tests at both cotyledon and three-expanded leaf stages using 38 entries, including USDA inbreds and commercial hybrids, were conducted in randomized complete-block designs. In these tests, every leaf of each plant was thoroughly sprayed with P. parasitica isolate PP1 at a concentration of 10,000 sporangia per ml at both stages. Ratings for downy mildew reaction phenotype were made at 9 days postinoculation on a 0-9 scale of increasing disease severity. We found significant phenotypic variation to infection among broccoli entries. We observed three general phenotypes: 1) resistance at both stages; 2) susceptible at cotyledon stage combined with resistance at three-expanded leaf stage; and 3) susceptibility at both stages. Additionally, inoculation at the cotyledon stage had no effect on inoculation at the three-expanded leaf stage.

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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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Integration of early disease-resistance phenotyping, histological characterization, and transcriptome sequencing reveals insights into downy mildew resistance in impatiens

Horticulture Research ◽

10.1038/s41438-021-00543-w ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Ze Peng ◽

Yanhong He ◽

Saroj Parajuli ◽

Qian You ◽

Weining Wang ◽

...

Keyword(s):

Disease Resistance ◽

Downy Mildew ◽

Transcriptome Sequencing ◽

Early Stage ◽

Economic Losses ◽

Potential Candidate ◽

Early Disease ◽

True Leaf ◽

Cotyledon Stage ◽

Wide Range

AbstractDowny mildew (DM), caused by obligate parasitic oomycetes, is a destructive disease for a wide range of crops worldwide. Recent outbreaks of impatiens downy mildew (IDM) in many countries have caused huge economic losses. A system to reveal plant–pathogen interactions in the early stage of infection and quickly assess resistance/susceptibility of plants to DM is desired. In this study, we established an early and rapid system to achieve these goals using impatiens as a model. Thirty-two cultivars of Impatiens walleriana and I. hawkeri were evaluated for their responses to IDM at cotyledon, first/second pair of true leaf, and mature plant stages. All I. walleriana cultivars were highly susceptible to IDM. While all I. hawkeri cultivars were resistant to IDM starting at the first true leaf stage, many (14/16) were susceptible to IDM at the cotyledon stage. Two cultivars showed resistance even at the cotyledon stage. Histological characterization showed that the resistance mechanism of the I. hawkeri cultivars resembles that in grapevine and type II resistance in sunflower. By integrating full-length transcriptome sequencing (Iso-Seq) and RNA-Seq, we constructed the first reference transcriptome for Impatiens comprised of 48,758 sequences with an N50 length of 2060 bp. Comparative transcriptome and qRT-PCR analyses revealed strong candidate genes for IDM resistance, including three resistance genes orthologous to the sunflower gene RGC203, a potential candidate associated with DM resistance. Our approach of integrating early disease-resistance phenotyping, histological characterization, and transcriptome analysis lay a solid foundation to improve DM resistance in impatiens and may provide a model for other crops.

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