Abstract
There is a wealth of resistance genes in the Mexican wild relative of cultivated Solanum, but very few of these species are sexually compatible with cultivated Solanum tuberosum. The most devastating disease of potato is late blight caused by the oomycete Phytophthora infestans (Pi). The wild hexaploid species S. demissum, 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 Pi 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 (Rpi) conferring resistance to Pi were identified and cloned from the sexually incompatible species S. bulbocastanum: Rpi-blb1 (RB), Rpi-blb2, Rpi-blb3, and Rpi-bt1. For this research, a resistant S. bulbocastanum accession was selected carrying the genes Rpi-blb1 and Rpi-blb3 together with race-specific R3a and R3b 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., BC1 and BC2) 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 Avr 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 BC2 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 Avr effectors is an efficient approach for the successful identification and introgression of late blight resistance genes into the potato gene pool.
Highlights
Late blight caused by Phytophthora infestans (Mont.) de Bary (Pi) is one of the most damaging diseases of potatoes as it does affect the above ground parts of the plants and the tubers (Colton et al, 2006)
Using specific markers it was possible to demonstrate the presence of the following resistance genes in blb41: Rpi-blb1, Rpi-blb3, R3a, and R3b and confirm their transfer into somatic hybrids (SHs) and introgression into derived BC progenies (Figure 1, Tables 1–3, and Supplementary Figure S1)
Somatic hybridization and the identification of resistance genes using gene-specific markers were used to transfer a stack of genes determining durable resistance to late blight (Rpi-blb1 and Rpiblb3) and the race-specific genes (R3a and R3b) into the potato cv
Summary
Late blight caused by Phytophthora infestans (Mont.) de Bary (Pi) is one of the most damaging diseases of potatoes as it does affect the above ground parts of the plants and the tubers (Colton et al, 2006). Its potential in causing an epidemic coupled with its great adaptability led to many outbreaks and destructions of potato harvests during the course of human history (Vreugdenhil, 2007; Chakrabarti et al, 2017). Current disease control relies on ten up to 16 fungicide applications per season (Hanson et al, 2007; Haverkort et al, 2009). Fungicides are costly but they pollute the environment and affect human health (Paro et al, 2012). Late blight resistance introduced into potato cultivars by classical breeding, based on eleven race-specific resistance genes from S. demissum was quickly overcome by new races of Pi
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