AUTHOR=Rakosy-Tican Elena , Thieme Ramona , König Janine , Nachtigall Marion , Hammann Thilo , Denes Tunde-Eva , Kruppa Klaudia , Molnár-Láng Márta 

TITLE=Introgression of Two Broad-Spectrum Late Blight Resistance Genes, Rpi-Blb1 and Rpi-Blb3, From Solanum bulbocastanum Dun Plus Race-Specific R Genes Into Potato Pre-breeding Lines

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.00699

DOI=10.3389/fpls.2020.00699

ISSN=1664-462X

ABSTRACT=<p>There is a wealth of resistance genes in the Mexican wild relative of cultivated <italic>Solanum</italic>, but very few of these species are sexually compatible with cultivated <italic>Solanum tuberosum.</italic> The most devastating disease of potato is late blight caused by the oomycete <italic>Phytophthora infestans</italic> (<italic>Pi</italic>). The wild hexaploid species <italic>S. demissum</italic>, which it is able to cross with potato, was used to transfer eleven race-specific genes by introgressive hybridization that were subsequently widely used in potato breeding. However, there are now more virulent races of <italic>Pi</italic> that can overcome all of these genes. The most sustainable strategy for protecting potatoes from late blight is to pyramid or stack broad-spectrum resistance genes into the cultivars. Recently four broad-spectrum genes (<italic>Rpi</italic>) conferring resistance to <italic>Pi</italic> were identified and cloned from the sexually incompatible species <italic>S. bulbocastanum</italic>: <italic>Rpi-blb1</italic> (RB), <italic>Rpi-blb</italic>2, <italic>Rpi-blb</italic>3, and <italic>Rpi-bt1</italic>. For this research, a resistant <italic>S. bulbocastanum</italic> accession was selected carrying the genes <italic>Rpi-blb1</italic> and <italic>Rpi-blb3</italic> together with race-specific <italic>R3a</italic> and <italic>R3b</italic> genes. This accession was previously used to produce a large number of somatic hybrids (SHs) with five commercial potato cultivars using protoplast electrofusion. In this study, three SHs with cv. ‘Delikat’ were selected and backcross generations (i.e., BC<sub>1</sub> and BC<sub>2</sub>) were obtained using cvs. ‘Baltica’, ‘Quarta’, ‘Romanze’, and ‘Sarpo Mira’. Their assessment using gene-specific markers demonstrates that these genes are present in the SHs and their BC progenies. We identified plants carrying all four genes that were resistant to foliage blight in greenhouse and field trials. Functionality of the genes was shown by using agro-infiltration with the effectors of corresponding <italic>Avr</italic> genes. For a number of hybrids and BC clones yield and tuber number were not significantly different from that of the parent cultivar ‘Delikat’ in field trials. The evaluation of agronomic traits of selected BC<sub>2</sub> clones and of their processing qualities revealed valuable material for breeding late blight durable resistant potato. We show that the combination of somatic hybridization with the additional use of gene specific markers and corresponding <italic>Avr</italic> effectors is an efficient approach for the successful identification and introgression of late blight resistance genes into the potato gene pool.</p>