New North American isolates of Venturia inaequalis can overcome apple scab resistance of Malus floribunda 821 (original) (raw)
Related papers
Characterization of Venturia inaequalis pathogenicity on leaf discs of apple trees
European Journal of Plant Pathology - EUR J PLANT PATHOLOGY, 1998
Characterization of pathogenicity on whole plants is required to study host-pathogen interactions between Malus × domestica and Venturia inaequalis. We studied the reliability of an in vitro test of pathogenicity on leaf discs. Three strains of V. inaequalis (races 1, 6 and an English race) were inoculated in vitro onto a range of 16 Malus sp. clones including susceptible and resistant clones. The results were compared to those previously obtained in vivo. Resistant clones contained the main major known genes, i.e. Va, Vb, Vbj, Vf, Vg, Vm and Vr. Scab severity and the sporulation of the fungus were assessed 21 days after the inoculation date. The results indicated that it was possible to reproduce incompatible and compatible situations in vitro. A null severity corresponded to the avirulence of the strain for the clone considered. The resistance given by the Vb, Vbj, Vf, Vg, Vm and Vr genes were expressed in vitro. Only the clone carrying the Va gene and inoculated with the race 6 s...
CABI Agriculture and Bioscience
Background Breeding for resistance to apple scab (caused by Venturia inaequalis), the most devastating fungal disease of apples, relies on genetic resources maintained in germplasm collections. Methods To identify new sources of scab resistance, we evaluated 177 Malus accessions, including 27 primary and 13 hybrid Malus species from diverse geographical origins, in an orchard at Geneva, New York. We also screened a differential host set for 2 years to monitor for changes in the effectiveness of ten known scab resistance genes, which allowed us to confirm the presence of virulent pathogen races in the orchard. Results We found that ~ 37% of the wild Malus accessions and domesticated cultivars were resistant to apple scab in the field. Several of these accessions were unrelated to sources of previously known resistance genes and are promising for apple scab genetic research and resistance breeding. Cultivars carrying the Rvi6 (Vf) gene from Malus floribunda clone 821, e.g. ‘Liberty’ o...
European Journal of Plant Pathology, 2016
The aim of this study was to confirm the presence of races in populations of the fungus Venturia inaequalis that are able to overcome specific apple scab resistance gene(s) within the major apple-growing areas of Poland. The monitoring was conducted in six orchards located in the north, centre and south of Poland. The study involved the use of 16 differential genotypes for pathogenicity testing conducted under both greenhouse and orchard conditions. In addition, the occurrence of apple scab on 10 apple cultivars containing the Rvi6 gene was assessed in four organic orchards in central Poland. Apple scab was found on their leaves for the first time in Poland in 2010. The use of differential genotypes containing specific resistance genes suggested that 10 apple scab resistance genes had been overcome by V. inaequalis in the orchards monitored in this study.
Phytopathology, 2004
Calenge, F., Faure, A., Goerre, M., Gebhardt, C., Van de Weg, W. E., Parisi, L., and Durel, C.-E. 2004. Quantitative trait loci (QTL) analysis reveals both broad-spectrum and isolate-specific QTL for scab resistance in an apple progeny challenged with eight isolates of Venturia inaequalis. Phytopathology 94:370-379.
Our study analyzed four apple cultivars (Liberty, Florina, Starkrimson, Golden Spur) used as genitors, and theirs hybrid seedlings resulted from a diallel genitor crossing scheme, for revealing monogenic Vf resistance to scab. Seedlings of F 1 hybrids were selected based on the presence or absence of the scab infection symptoms on the leaves. The field morphological selection was completed by the laboratory marker assisted selection (MAS). Two specific molecular markers AL-07 (SCAR) and AM-19 (SCAR) were used for the screening of Vf gene presence, introgressed from Malus floribunda 821. Florina and Liberty cultivars were identified as heterozygous scab resistant parents with genotype Vfvf and Starkrimson and Golden Spur were scab susceptible cultivars with recessive homozygous genotype vfvf. We analysed 60 apple F 1 hybrids, grouped in six combinations. We obtained almost 1:1 Mendelian ratio as response (28 resistant : 32 susceptible) to the scab pathogen infection.
Phytopathology, 2004
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 (F(ST) > 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...
BMC evolutionary biology, 2018
Tracking newly emergent virulent populations in agroecosystems provides an opportunity to increase our understanding of the co-evolution dynamics of pathogens and their hosts. On the one hand host plants exert selective pressure on pathogen populations, thus dividing them into subpopulations of different virulence, while on the other hand they create an opportunity for secondary contact between the two divergent populations on one tree. The main objectives of the study were to explore whether the previously reported structure between two Venturia inaequalis population types, virulent or avirulent towards Malus x domestica cultivars carrying Rvi6 gene, is maintained or broken several years after the first emergence of new virulent strains in Poland, and to investigate the relationship between 'new' and 'native' populations derived from the same commercial orchards. For this purpose, we investigated the genetic structure of populations of the apple scab fungus, occurri...
Population variation of apple scab (Venturia inaequalis) within mixed orchards in the UK
European Journal of Plant Pathology, 2012
Apple scab, caused by Venturia inaequalis, is one of the most important apple diseases worldwide. To investigate between-and within-orchard fungal variability, 212 isolates were sampled from two mixed orchards, one of 10 years of age and the other of 45 years of age, in the UK and genotyped with AFLP and SSR markers. Populations of isolates from the two orchards did not differ significantly in terms of allele frequencies at the screened AFLP and SSR loci. However, groups of isolates from individual cultivars differed significantly within each orchard and there were also significant differences between groups of isolates from individual trees of the same cultivar in the same orchard. These differences were less pronounced in the younger mixed orchard than in the older one. The existence of tree-to-tree fungal variability indicates a possible role for conidia as a source of primary inoculum. Non-random mating may be one of the factors causing the significant differences among fungal populations from different cultivars. These results suggest that apparently 'susceptible' cultivars have different background genetic resistance factors, which can be exploited for disease management in mixtures.
2015
Apple scab caused by Venturia inaequalis is the major constraint to apple production worldwide. Today, an intensive use of pesticide is required to protect commercial orchards planted with cultivars (cvs) highly susceptible to scab. This intensive use of pesticides costs, and has a detrimental impact on the consumer health and the environment, but could be largely reduced by the introduction of resistant or partially resistant scab cvs in the orchard. This thesis aims to provide new insights into the mechanisms of resistance of two cvs presenting contrasting resistance phenotypes and durability: the durable partial resistance in ‘Président Roulin’ and the non durable resistance in ‘Geneva’, harboring a complex of complete and partial effects R genes. Preliminary, phytopathological tests were used in both cvs to differentiate the resistance loci. Resistance in both cultivars were shown to be race-specific and governed by at least five resistance loci. Expression signature of the part...