Field apple scab susceptibility of a diverse Malus germplasm collection identifies potential sources of resistance for apple breeding

Abstract

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’ or ‘Florina’, remained resistant despite the breakdown of Rvi6. ‘Demir’, a Malus hybrid from Turkey, and ‘Chisel Jersey’, a traditional English hard cider cultivar, showed fewer symptoms than the Rvi6 resistant cultivar ‘Prima’. Races 1 to 7 and 9 of V. inaequalis were present in the orchard, but no scab was observed on the indicator host accessions for races 11 and 12. Conclusions Detailed and systematic screening of Malus germplasm identified resistant and moderately resistant donor accessions based on resistance reaction types. These accessions are promising for use in future genetic studies to identify novel sources of scab resistance alleles for apple breeding to develop cultivars with durable apple scab resistance.

Evaluation of Apple Scab and Occurrence of Venturia Inaequalis Races on Differential Malus Genotypes in Latvia

“…Scab resistance has been in focus for decades in breeding programmes worldwide, resulting in many scab-resistant cultivars (Benaouf and Parisi, 2000;Bowen et al, 2011;Kaufmane et al, 2013). Most modern scab resistant apple cultivars carry a single resistance gene, Rvi6, widely exploited in breeding programmes worldwide, but the selection has also been performed for other resistance (R) genes (Janick, 2002;Ikase, 2015;Papp et al, 2020). Resistance gene pyramiding in the breeding and growing of cultivars with at least two or more resistance genes and planting of different genotypes instead of mono-cultivar orchards are recommended to ensure longterm and stable resistance to apple scab (Lespinasse et al, 2000;Bus et al, 2011;Bastiaanse et al, 2016).…”

Bacterial Endophyte Community Dynamics in Apple (Malus domestica Borkh.) Germplasm and Their Evaluation for Scab Management Strategies

“…The modern horticultural practices demand chemical-centered strategies for phytopathogen management and emphasize alternative control measures focused on the use of products that induce resistance against the diseases [12], as the present pesticide intensive strategies have led to ecological degradation, inducing detrimental environmental effects beyond the huge effect on the economy of the farming community. One of the alternatives to these practices could be natural chemicals based on copper or sulfur, but due to their efficacy on pathogens as well as the advent of phytotoxicity apprehensions, these compounds have also had little impact on scab management strategies.…”

A phased, chromosome-scale genome of ‘Honeycrisp’ apple (Malus domestica)

“…In fact, nine new cultivars derived from 'Honeycrisp' are already on the market. Disease resistance, critical for sustainable apple production, has historically been less important due to a market dominated by modern cultivars bred primarily for fruit quality and intensive conventional production systems [11]. Most apple cultivars grown commercially in the US are susceptible to fungal diseases such as apple scab.…”