Mapping and DNA sequence characterisation of the Ry_sto locus conferring extreme virus resistance to potato cultivar ‘White Lady’

Abstract

23Virus resistance genes carried by wild plant species are valuable resources for plant 24 breeding. The Ry sto gene, conferring a broad spectrum of durable resistance, originated from 25 Solanum stoloniferum and was introgressed into several commercial potato cultivars, 26 including 'White Lady', by classical breeding. Ry sto was mapped to chromosome XII in 27 potato, and markers used for marker-assisted selection in breeding programmes were 28 identified. Nevertheless, there was no information on the identity of the Ry sto gene. To begin 29 to reveal the identification of Ry sto , fine-scale genetic mapping was performed which, in 30 combination with chromosome walking, narrowed down the locus of the gene to 31 approximately 1 Mb. DNA sequence analysis of the locus identified six full-length NBS-LRR-32 type (short NLR-type) putative resistance genes. Two of them, designated TMV2 and TMV3, 33 were similar to a TMV resistance gene isolated from tobacco and to Y-1, which co-segregates 34 with Ry adg , the extreme virus resistance gene originated from Solanum andigena and localised 35 to chromosome XI. Furthermore, TMV2 of 'White Lady' was found to be 95% identical at the 36 genomic sequence level with the recently isolated Ry sto gene of the potato cultivar 'Alicja'. In 37 addition to the markers identified earlier, this work generated five tightly linked new markers 38 which can serve potato breeding efforts for extreme virus resistance. 39 40 3 41 Introduction 42 43 For sustainable intensification of crop production, disease control should, when 44 possible, be achieved using genetics rather than using costly recurrent chemical sprays. Wild 45 relatives of crop plants are a good source of genes for disease resistance. Potato (Solanum 46 tuberosum), the world's fourth most important food crop, following maize, wheat and rice, 47 can be crossed with a number of wild Solanum species. Nevertheless, classical breeding for 48 resistance is time-consuming, and it is extremely difficult to recover the parental combination 49 necessary for beneficial alleles in the progeny. Thus, there is great value in genetic 50 approaches that can improve disease resistance in potato varieties without disrupting 51 favourable combinations of alleles [1]. 52 One of the major factors adversely affecting potato production worldwide is virus 53 infection. Viruses such as Potato leafroll virus (PLRV) and Potato virus Y (PVY) can affect 54 yield substantially, with up to 80% losses, while viruses producing mild or latent symptoms, 55 such as Potato virus X (PVX) and Potato virus S (PVS), show yield losses of at most 10 to 56 20% [2]. Host plants can exhibit compatible or incompatible interactions with a virus. In a 57 compatible interaction, potato plants can be either tolerant, accumulating high titres of the 58 virus without symptoms, or sensitive, responding to viral infection with development of 59 disease. In an incompatible interaction, the plants respond to viral infection with a 60 hypersensitive reaction (HR) or an extreme resistan...