Late blight (Phytophthora infestans) (P.i.) is the most serious disease in potato production worldwide and causes tremendous losses in yield and high costs in chemical plant protection. A worthwhile approach to combat the disease is breeding for late-blight resistance. Wild species of potato are potential sources of P.i.- resistance genes. In the past, though, genes conferring race-specific resistance were rapidly overcome due to the extremely high adaptation rate of the pathogen. An alternative strategy in breeding for resistance is to use quantitative or non-specific resistance allowing the survival of late blight on a low level without genetic adaptation. In a long-term breeding programme at Groß Lüsewitz Experimental Station, several wild species have been used for many years. In 2007 and 2008 a series of advanced breeding clones from a backcross programme involving different wild relatives were investigated for their reaction to late blight. A maturitycorrected score was used to separate resistance and late-maturity effects. We describe 11 breeding clones which display higher degrees of quantitative P.i.- resistance in the field combined with earlier maturity as compared to standard varieties. Besides, the clones showed high resistance against tuber blight, too. Notably, besides improved resistance to P.i. these clones possess acceptable agronomic traits with regard to starch content, suitability for crisp and chips production and acceptable levels of table quality, respectively.

Seventy-two potato cultivars have been bred at the Scottish Plant Breeding Station and the Scottish Crop Research Institute since 1920. The original genetic base contained resistance to wart disease and to viruses, but not comprehensive resistance to all strains. Introgression of resistance genes from the wild and cultivated potato species of Latin America started for late blight in 1932, for viruses in 1941 and for potato cyst nematodes in 1952. Just seven of the 219 wild tuber-bearing species recognized by Hawkes in 1990 feature in the pedigrees of our cultivars, with Solanum demissum for blight resistance in 58, S. vernei for nematode resistance in 19 and S. microdontum for Potato virus Y resistance in 15, the other four species being S. multidissectum, S. commersonii, S. maglia and S. acaule. Resistance to other fungal and bacterial diseases has been mainly due to chance rather than deliberate breeding. From 1970, selection for yield and quality included processing quality, and despite lack of commercial success, prospects remain good for cultivars resistant to sweetening during cold storage. Since 1990 prebreeding has combined desirable traits through efficient recurrent selection based on progeny testing and provided parents for the commercially funded breeding of finished cultivars. Only one cultivar is a Neotuberosum-Tuberosum hybrid, whereas 15 cultivars have the H1 gene for resistance to Globodera rostochiensis introgressed from group Andigena. Long-day Phureja cultivars are finding a market niche for their flavour attributes. Breeding strategies and methods are critically reviewed from a genetic viewpoint.

Sub-project 5 of BIOEXPLOIT aims to design durable disease resistance through marker-assisted breeding by converting existing markers for high-throughput application, developing and validating high-throughput marker technologies and pyramiding major R genes and/or quantitative trait loci into elite material. Activities include (1) the fine mapping of the quantitative trait locus PiXspg which accounts for a large proportion of the variation in late blight resistance, (2) converting SNP-based markers and an AFLP marker to easy-to-use-markers, (3) testing of progenies with combined sources of late blight resistance for presence of R genes and agronomic features, (4) backcrossing new sources of resistance to S. tuberosum and molecular screening of breeding materials with marker GP94 linked with gene Rpi-phu1 conferring late blight resistance, (5) evaluating potato clones with enhanced resistance against Phytophthora infestans under field conditions of Toluca (México), and (6) developing populations and marker-assisted breeding for disease resistance.

The EU Framework 6 Integrated Project BIOEXPLOIT concerns the exploitation of natural plant biodiversity for the pesticide-free production of food. It focuses on the pathogens Phytophthora infestans, Septoria tritici, Blumeria graminis, Puccinia spp. and Fusarium spp. and on the crops wheat, barley, tomato and potato. The project commenced in October 2005, comprises 45 laboratories in 12 countries, and is carried out by partners from research institutes, universities, private companies and small-medium enterprises. The project has four strategic objectives covered in eight sub-projects. These objectives relate to (i) understanding the molecular components involved in durable disease resistance, (ii) exploring and exploiting the natural biodiversity in disease resistance, (iii) accelerating the introduction of marker-assisted breeding and genetic engineering in the EU plant breeding industry, and (iv) coordinating and integrating resistance breeding research, providing training in new technologies, disseminating the results, and transferring knowledge and technologies to the industry.

Potato (Solanum tuberosum) germplasm was tested for resistance to stem colonization by the black dot pathogen Colletotrichum coccodes. Forty-six potato selections were tested in three field trials from 2006 to 2008. Resistance was determined by comparing disease severity on aboveground stems to the mean disease severity of the industry standards Russet Burbank, Ranger Russet, and Umatilla Russet. The potato selections were also tested for genotype*environment interaction to determine their genetic stability. Heritability of resistance was calculated to be 0.13 with confidence intervals between 0.00 and 0.68. The selections A0012-5, PA95B2-4, PA98NM38-1, and PO94A009-7 had less black dot than the standards in all years, and also demonstrated genetic stability. These selections also possess resistance to the root galling stage of the powdery scab pathogen Spongospora subterranea f. sp. subterranea. PA95B2-4, PA98NM38-1, and PO94009-7 were derived from an introgression program to incorporate resistance to the Columbia root-knot nematode Meloidogyne chitwoodi from the Mexican wild species Solanum bulbocastanum, and also have the commercial cultivar Summit Russet in their ancestry. These selections are promising steps toward sustainable management of black dot and powdery scab and will be further tested and used for breeding purposes.

Potato is an important crop, grown worldwide. It suffers from many pests and diseases among which late blight, caused by the oomycete Phytophthora infestans, is the worst. The disease is still causing major damage in many potato production areas and control is only possible by applying fungicides frequently. The knowledge on the molecular biology and genetics of the interaction between the plant and the oomycete is developing rapidly. These are relevant fields of study, currently dominated by the discovery of many resistance genes and numerous effector proteins and the analysis of their specific mode of action. These studies may yield essential information needed for the development of durable resistance. The long-term and worldwide effort to breed for resistance so far has had little effect. A novel breeding approach may change this. It is based on cisgenic modification (CM) consisting of marker-free pyramiding of several resistance genes and their spatial and temporal deployment yielding dynamic varieties that contain potato genes only. It is envisioned that this CM approach with potato's own genes will not only prove societally acceptable but may also result in simplifications in the legislation on use of the CM approach. Various parties in the potato research arena intend to cooperate in this novel approach in a number of developing countries where potato substantially contributes to food security. The use of resources such as land, water and energy improves when the effect of late blight is markedly reduced.

A diploid hybrid Solanum phureja x S. stenotomum population that has shown relatively high levels of quantitative resistance to late blight was used to develop polymerase chain reaction (PCR)-based markers for marker-assisted selection (MAS) of disease resistance in potato breeding. Two random amplified polymorphic DNA (RAPD) markers, OPA03(576) and OPA17(559), were identified as being linked to partial resistance. OPA03(576) was found to be associated in coupling phase while OPA17(559) showed association in repulsion phase to resistance. These two markers, together with previously developed amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers, were incorporated into an existing restriction fragment length polymorphism (RFLP)-based chromosomal linkage map of this S. phureja x S. stenotomum population. Linkage analysis located the OPA17(559) marker on chromosome III, 12 cM away from a major quantitative trait locus (QTL) that explained 23.4% of the total phenotypic variation for late blight resistance. Marker OPA03(576) was located in the distal region of chromosome XII where several resistance genes are found clustered. A third PCR-based marker, GP198F-1, derived from the original RFLP marker GP198, was linked to the late blight resistance QTL on chromosome III that explained 23.4% of the total phenotypic variation in this population. The three PCR-based markers were used to screen for their presence in the mapping population and high correlations between the presence of these markers and late blight resistance were found. Our results suggest that these markers may be useful for MAS of late blight resistance in potato breeding programs.

This study was carried out to select potato (Solanum tuberosum) clones resistant to Bacterial wilt (BW) disease (Ralstonia solanacearum) and evaluate genetic diversity with RAPD (Randomly amplified polymorphic DNA). A total of 440 clones collected and maintained at Highland Agriculture Research Center were tested in the hydroponic culture system with R. solanacearum race 1 and 3. After 40 days in dipping in hydroponic culture system, the resistance was evaluated as the range from 0 (resistance) to 4 (susceptible). Seventy-two clones were selected in the first screening as a resistant to race 1 or 3 in 2007, and the selected lines were tested again as the same procedure above. After the second screening, a total of 20 lines were selected as resistance to BW in 2008. For the evaluation of genetic diversity of the selected 20 clones, RAPD analysis was carried out with potato URP primer sets. From the 11 URP primers, 5 to 7 polymorphic DNA bands were amplified in selected resistant clones with each primer. With RAPD analysis, the genetic similarity was shown from 0.56 to 0.82. The selected clones were separated into two distinct groups at the genetic similarity value point of 0.56. Four clones including AG14252 were integrated into the first group, and the others, 16 clones, were grouped in the second group. In the second group, the two sub-groups showed genetic similarity value of 0.59. Seven clones including AG34326 and nine clones were separated into the first and second sub-groups, respectively. The results have revealed that bacterial wilt resistance test using hydroponic culture is favorable for the selection of BW resistant potato clones, and that RAPD analysis is useful for the identification of genetic similarity. The selected potato clones could be used as parent clones in BW resistance breeding program of potatoes.

The use of culture filtrate of Alternaria solani in the differentiation of susceptible and resistant potato genotypes has been described in scientific literature. However, few researches take into account the role of isolates of A. solani and other factors affecting the production of culture filtrate to use in vitro selection as a tool. This allows plant breeders to reduce the time to obtained new varieties of potato. This study aimed to establish a protocol for in vitro selection of potato plants resistant to early blight with the use of culture filtrate of Alternaria solani Sor, in support to the potato Genetic Improvement Program. The proposed protocol related aspects such as: obtaining of culture filtrate, characteristics of A. solani isolates and plant material, as well as, the descriptive scale for assessing the effect of culture filtrate on potato plants (Solanum tuberosum L.) var. Desirée. The protocol can be used as a useful tool in early stage trials to evaluate the resistance to A. solani in potato genotypes obtained by any method of genetic improvement to this disease. This contributes to increased efficiency of selection in natural conditions. The number of individuals to evaluate in field decreases. In these conditions other factors affect the differentiation of susceptible and resistant genotypes. Keywords: Desirée, breeding program, early blight