Somatic variation plays a key role in the evolution of the Vf gene family residing in the Vf locus that confers resistance to apple scab disease

An apple breeding program has been carried out at the Department of Fruit Science for more than a decade. Several apple selections have been released from the progenies of crosses in 1992 and 1993. Six candidates were submitted for national recognition out of the hybrids examined for more than a decade. The six selections are resistant against all the three most important apple diseases (apple scab, powdery mildew and fire blight). Scab resistance is controlled by the Vf gene originating from the species Malus floribunda 821 and transmitted by cultivar Prima. Heterozygote Vfvf genotype of the six cultivar candidates was proved by molecular genetic examinations of Dept. Genetics and Plant Breeding. Characteristics of these selections from 'Prima' progenies are shown on the base of our own observations.

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Development of sequence-characterized amplified regions (SCARs) from amplified fragment length polymorphism (AFLP) markers tightly linked to the Vf gene in apple

Genome ◽

10.1139/g00-103 ◽

2001 ◽

Vol 44 (1) ◽

pp. 63-70 ◽

Cited By ~ 20

Author(s):

Mingliang Xu ◽

Ernesto Huaracha ◽

Schuyler S Korban

Keyword(s):

Length Polymorphism ◽

Fragment Length ◽

Fragment Length Polymorphism ◽

Apple Scab ◽

Amplified Fragment Length Polymorphism ◽

Genetic Distances ◽

Aflp Markers ◽

Scab Resistance ◽

Scar Markers ◽

Vf Gene

Amplified fragment length polymorphism (AFLP) markers have become widely used in saturating the region of a gene of interest for the ultimate goal of map-based cloning of the gene or for marker-assisted selection. However, conversion of AFLP markers into restriction fragment length polymorphism (RFLP) or polymerase chain reaction (PCR)-based markers will greatly expand their usefulness in genetic applications. Previously, we have identified 15 AFLP markers tightly linked to the Vf gene conferring scab resistance in apple. In this study, we have successfully converted 11 of these AFLPs into sequence-characterized amplified region (SCAR) markers. Of the remaining four nonconverted AFLP markers, one, ET2MC8-1, has been found to be very short (83 base pairs) and is an A/T rich (90%) marker; a second, EA2MG11-1, has shown identical sequences between Malus floribunda 821 (the original source of the Vf gene) and scab-susceptible apple cultivars; while the other two, EA12MG16-1 and ET8MG1-1, have not been cloned. Using the 11 converted SCAR markers along with 5 previously identified SCAR markers, a high-resolution linkage map around the Vf gene has been constructed, and found to be consistent with its corresponding AFLP map. Three converted SCAR markers (ACS-3, -7, and -9) are inseparable from the Vf gene; whereas one (ACS-6) is located left of, and the remaining seven (ACS-1, -2, -4, -5, -8, -10, and -11) are located right of the Vf gene at genetic distances of 0.4 and 0.2 cM, respectively. A reliable and robust procedure for development of SCAR markers from AFLP markers is presented.Key words: apple, AFLP, SCAR, apple scab disease, Vf gene.

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A bacterial artificial chromosome (BAC) library of Malus floribunda 821 and contig construction for positional cloning of the apple scab resistance gene Vf

Genome ◽

10.1139/g01-105 ◽

2001 ◽

Vol 44 (6) ◽

pp. 1104-1113 ◽

Cited By ~ 12

Author(s):

Mingliang Xu ◽

Junqi Song ◽

Zhukuan Cheng ◽

Jiming Jiang ◽

Schuyler S Korban

Keyword(s):

Positional Cloning ◽

Apple Scab ◽

Bac Library ◽

Artificial Chromosome ◽

Scab Resistance ◽

Vf Gene ◽

Bac Clones ◽

Malus Floribunda ◽

Sequence Characterized Amplified Regions

The apple scab resistance gene Vf, originating from the wild species Malus floribunda 821, has been incorporated into a wide variety of apple cultivars through a classical breeding program. With the aim of isolating the Vf gene, a bacterial artificial chromosome (BAC) library consisting of 31 584 clones has been constructed from M. floribunda 821. From the analysis of 88 randomly selected BAC clones, the average insert size is estimated at 125 kb. If it is assumed that the genome size of M. floribunda 821 is 769 Mb/haploid, the library represents about 5× haploid genome equivalents. This provides a 99% probability of finding any specific sequence from this library. PCR-based screening of the library has been carried out using eight random genomic sequence-characterized amplified regions (SCARs), chloroplast- and mitochondria-specific SCARs, and 13 high-density Vf-linked SCAR markers. An average of five positive BAC clones per random SCAR has been obtained, whereas less than 1% of BAC clones are derived from the chloroplast or mitochondrial genomes. Most BAC clones identified with Vf-linked SCAR markers are physically linked. Three BAC contigs along the Vf region have been obtained by assembling physically linked BAC clones based on their fingerprints. The overlapping relatedness of BAC clones has been further confirmed by cytogenetic mapping using fiber fluorescence in situ hybridization (fiber-FISH). The M. floribunda 821 BAC library provides a valuable genetic resource not only for map-based cloning of the Vf gene, but also for finding many other important genes for improving the cultivated apple.Key words: apple, resistance Vf gene, BAC library, sequence-characterized amplified regions (SCARs), fiber fluorescence in situ hybridization (fiber-FISH), positional cloning.

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Molecular Screening of Some Apple Progenies for Detection Vf Gene Using Marker Assisted Selection

Bulletin of University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca Horticulture ◽

10.15835/buasvmcn-hort:2021.0022 ◽

2021 ◽

Vol 78 (2) ◽

pp. 36

Author(s):

Georgeta BIVOLARIU (GUZU) ◽

Ioan ZAGRAI ◽

Luminița ZAGRAI ◽

Mirela Irina CORDEA ◽

Claudiu MOLDOVAN

Keyword(s):

Resistance Gene ◽

Fruit Quality ◽

Marker Assisted Selection ◽

Venturia Inaequalis ◽

Apple Scab ◽

Molecular Screening ◽

Breeding Programs ◽

Vf Gene ◽

Local Variety ◽

Malus Floribunda

Apple scab, caused by Venturia inaequalis is one of the most damaging pathogens that affects apple species. Cross combinations were made between Auriu de Bistrița cv. (female genitor) - a valuable local variety in terms of fruit quality but only tolerant to scab, and Florina cv. (male genitor) used as a donor of Vf resistance gene. It was first detected in Malus floribunda Clone 821, which was later transferred to commercial varieties by different breeding programs. To confirm the presence of Vf gene, progenies resulting from the mentioned combination were tested with MAS (Marker Assited Selection), using two dominant primers pairs (AM19, U1400), and another one codominant (AL07) used to distinguish homozygous and heterozygous genotypes. After the crossing combination, a number of twenty-six hybrids were obtained, of which 50% (13 hybrids) were clasified as resistant (heterozygous), respectively 50% (13 hybrids) as susceptible (recessive homozygotes), so the Mendelian ratio was confirmed.

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Breakdown of the Scab Resistance Gene Vf in Apple Leads to a Founder Effect in Populations of the Fungal Pathogen Venturia inaequalis

Phytopathology ◽

10.1094/phyto.2004.94.4.364 ◽

2004 ◽

Vol 94 (4) ◽

pp. 364-369 ◽

Cited By ~ 42

Author(s):

Fabien Guérin ◽

Bruno Le Cam

Keyword(s):

Resistance Gene ◽

Founder Effect ◽

Allelic Variation ◽

Venturia Inaequalis ◽

Apple Scab ◽

Apple Orchard ◽

Scab Resistance ◽

Vf Gene ◽

Major Resistance Gene ◽

High Level

The recent breakdown of Vf, a major resistance gene to apple scab, provided an opportunity to analyze a population genetic process within the matching virulent subpopulation of the fungus Venturia inaequalis. We utilized the amplified fragment length polymorphism technique and allelic variation at four microsatellite loci to assess genetic structure of 133 isolates of V. inaequalis from a single commercial apple orchard sampled from one cultivar carrying the Vf gene (Judeline) and three cultivars devoid of the Vf gene. Both analyses indicated a strong decrease of the genetic diversity among isolates from the Vf cultivar compared with the high level of diversity among isolates from the three other cultivars. This leads to a high genetic differentiation between virVf and avrVf groups (FST > 0.17). Analyses of the genetic distance between AFLP patterns based on the Jaccard index indicate that all virVf isolates could be assigned to a single clonal lineage. These results lead us to conclude that the clonal structure of the population isolated from the Vf cultivar is an example of a founder effect in response to a resistance gene breakdown and it is likely that this event occurred in the orchard during the sampling year.

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