Euphytica 108: 137–144, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands. 137 Characterisation of resistance to potato leafroll virus accumulation in Solanum phureja Liliana Franco-Lara 1,2 & Hugh Barker 1,∗ 1 Scottish Crop Research Institute, Invergowrie, Dundee, DD2 5DA, Scotland, United Kingdom; 2 permanent address: Facultad de Biologia Aplicada, Universidad Militar Nueva Granada, Carrera 11 No. 101-80 Bogota, Colombia; ( ∗ author for correspondence) Received 8 June 1998; accepted 12 March 1999 Key words: ELISA, genetic modification, PLRV, potato, Solanum phureja, virus resistance Summary Strong resistance to accumulation of potato leafroll virus (PLRV) was identified in a clone of the diploid potato species Solanum phureja (cv. ‘Egg Yolk’, clone 5010) using a quantitative enzyme-linked immunosorbent assay (ELISA). The resistance is expressed very strongly in leaf tissue (virus could not be detected in leaves of some plants although other tissues were infected) but less strongly in petiole and stem tissue of infected plants. The titre of PLRV in leaves of S. phureja (5010) is approximately 2%, or less, of the titre in S. tuberosum cv. Maris Piper. The pattern of virus accumulation in different tissues of S. phureja (5010) and the distribution of virus-infected cells in phloem bundles suggest that this resistance is different to a similar form of resistance to PLRV accumulation previously identified in clones of Solanum tuberosum. Plants of S. phureja (5010) were transformed with the coat protein gene of potato leafroll virus (PLRV). Transgenic lines of S. phureja (5010) expressing transgene RNA transcript were no more resistant to aphid-borne infection with PLRV or to virus accumulation than were non-transgenic lines. Introduction Solanum phureja is a cultivated diploid potato spe- cies with a centre of genetic diversity in the south of Colombia (Carrasco & Pineda, 1993) and is found in the Andes from Bolivia to Venezuela. It seems that S. phureja evolved from Solanum stenotomum by hu- man selection for rapid maturity and lack of tuber dormancy after harvest. Selection by Indian cultivat- ors might have been polyphyletic, thus many cultivars originated in different regions. In Colombia, several genotypes of S. phureja are grown commercially but only those that are collectively known as the variety ‘yema de huevo’ (‘Egg Yolk’) that produces yellow, round tubers are widely grown. Based on morpho- logical characteristics and electrophoretic patterns of total proteins at least 11 different genotypes have been identified in Colombia within the ‘Egg Yolk’ variety (Carrasco & Pineda, 1993; Carrasco, 1994). Nearly 10% of the total potato crop in Colombia is cv. ‘Egg Yolk’, although it is generally cultivated in small plots as a secondary crop accompanying the main crop, which is usually potato (Solanum tuberosum subsp. andigena). Tubers of cv. ‘Egg Yolk’ have excellent cooking characteristics and are more nutritious than those of S. tuberosum varieties. Infection of S. phureja is common with viruses such as potato leafroll virus (PLRV) and potato vir- uses S, X and Y (personal communication, L. Salazar, Centro Internacional de la Papa (CIP), Lima, Peru). Although no major surveys of virus infection using enzyme-linked immunosorbent assay (ELISA) have been made in Colombian crops of ‘Egg Yolk’, ob- servation of symptoms suggest that it is susceptible to PLRV and work in Colombia, has led to the conclusion that several genotypes of ‘Egg Yolk’ are severely affected by PLRV (personal communication, J.R. Artunduaga, Instituto Colombiano Agropecuario, Bogota, Colombia). However, there are no published reports on the susceptibility/resistance of S. phureja to