Development of Initial Material for Hybrid Breeding of Welsh Onion with Resistance to Downy Mildew

Relevance. The aim of our work was to create initial material for the breeding of F1 hybrids of Welsh onion (Allium fistulosum) with resistance to downy mildew.

Materials and Methods. To achieve this goal, interspecific hybridization was carried out using A. roylei (donor of the dominant resistance gene Pd1) and A. galanthum (donor of the Ga-type cytoplasm inducing CMS), followed by backcrossing with A. fistulosum (cultivar 'Ishikura' and self-pollinated lines from the 'Katana F1' hybrid). Pollen fertility was assessed using the acetocarmine staining method, calculating the proportion of stained grains in three fields of view. Evaluation of resistance/susceptibility of the obtained populations was conducted under an artificial infection background (inoculum of the pathogen Peronospora destructor at a concentration of 106 spores/ml), as well as using the molecular SCAR marker DMR1.

Results. It was found that first-generation hybrids (A. roylei × A. fistulosum) and (A. galanthum × A. fistulosum) are characterized by extremely low pollen fertility (17.9% and 14.9%, respectively), caused by meiotic disturbances during distant hybridization. However, a single backcross of the hybrid (A. roylei × A. fistulosum) with A. fistulosum led to a complete restoration of male fertility in the BC1 population, where the average fertility was 95.4%. Phenotypic analysis under the artificial infection background revealed an absence of downy mildew symptoms in all plants of the BC1 and its populations containing genetic material from A. roylei, which does not correspond to the expected monogenic dominant segregation. At the same time, PCR analysis with the DMR1 marker demonstrated the amplification of non-specific fragments (350, 490, and 580 bp) in BC1 plants, indicating structural rearrangements in the introgression region of the Pd1 gene. The study demonstrated the possibility of transferring the CMS-inducing factor from A. galanthum and the Pd1 resistance gene from Allium roylei into the genome of Welsh onion. The obtained BC populations represent valuable material for the breeding of heterotic Welsh onion hybrids resistant to downy mildew.

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