Molecular screening of the pear collection maintained at the Maikop Experiment Station of VIR for scab resistance gene markers

Background: Pear (Pyrus sp.) is one of the economically important fruit crops grown in 50 countries worldwide. However, pear cultivars are affected by many pathogens, including scab caused by the ascomycete fungus belonging to the genus Venturia Sacc. The two pear-damaging species of this genus are Venturia nashicola S. Tanaka & S. Yamam. that affects Asian pears (P. pyrifolia (Burm.fil.) Nakai, P. bretschneideri Rehder, P. ussuriensis Maxim.), and Venturia pirina Aderh. that affects specifically the European pear P. communis L. The use of molecular markers for the selection of scab-resistant varieties will improve the efficiency of breeding programs. The aim of this work was to test the markers of the Rvn2 and Vnk (Rvn1) genes, which control scab resistance to Venturia nashicola, using the material from the collection maintained at the Maikop Experiment Station, and accessions from a collecting mission. Materials and methods: A sample of 255 accessions was studied, including 246 cultivars from the collection of the Maikop Experiment Station, and nine accessions from the VIR collecting mission to the North Caucasus in 2022. The basis of the sample were 152 cultivars of Caucasian origin, including local forms; the second large subsample (61) was made up of European cultivars. The research used the markers of the Rvn2 gene – PSC217/XhoI and PSC234/HaeIII, and of the Vnk (Rvn1) gene – STS-OPO9/SalI and STS-OPAW13, selected from the literature. Results: A wide distribution of both markers of the Rvn2 gene among the accessions was shown (89.4% for PSC217/XhoI and 30.9% for PSC234/HaeIII), while the frequency of their occurrence among the two main subsamples was approximately the same. When comparing the molecular screening results with the data on the accessions resistance to pear scab, a low diagnostic value of both markers was shown – the PSC217/XhoI marker had an efficiency of 47.2%, and that of the PSC234/HaeIII marker was 51.4%. On the contrary, the STS-OPAW13 and STS-OPO9/SalI markers of the Vnk (Rvn1) gene were present only in single cultivars (seven) bred in China and the Caucasus. However, according to their pedigrees, the latter ones were created without the use of original local material. Conclusion. The study of a large sample of pear accessions has shown a wide distribution of Rvn2 gene markers in the studied material, which, however, demonstrated low efficiency and are unsuitable for molecular screening. The Vnk (Rvn1) gene markers were detected only in few accessions. Of interest for breeding is the Chinese cultivar ‘Dan-Shansu-li’, which has both markers of the gene Vnk (Rvn1), and exhibits resistance to pear scab.

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