Results of long-term assessment of potato (Solanum tuberosum) breeding lines of Scientific and Practical Center of the National Academy of Sciences of Belarus for Potato, Vegetable and Fruit Growing for resistance to causal agents of the main potato tuber rots in Belarus are presented. In course of the realized experiment there used the following fungi cultures: Fusariumn sambucinum; F. sambuicinum var. minus; F. oxysporum; Colletotrichum coccodes; Pythium ultimum. Immune and slightly affected samples are selected and recommended as parental lines for breeding varieties with high resistance to disease.

Late blight is a devastating disease in potato production world-wide. Breeding for resistance is complex because of the versatile and aggressive population of Phytophthora infestans, which overcomes any new genetic source of resistance very rapidly. There are reliable fungicides available to control the disease but chemical control is costly and harmful to the environment. There are no cultural practices reducing the infestation, which are reliable enough to cope with the disease in a non-chemical way. Given the close link between the physiological condition of the crop and its resistance to late blight, this paper addresses the question whether crop physiology can help to combat the disease. Although there are possibilities to (partly) escape to the late blight by advancing the crop cycle or the tuber bulking, it is concluded that crop physiology can do little to reliably reduce the susceptibility to late blight. Breeding for resistance remains the best option.

Late blight is a devastating disease in potato production world-wide. Breeding for resistance is complex because of the versatile and aggressive population of Phytophthora infestans, which overcomes any new genetic source of resistance very rapidly. There are reliable fungicides available to control the disease but chemical control is costly and harmful to the environment. There are no cultural practices reducing the infestation, which are reliable enough to cope with the disease in a non-chemical way. Given the close link between the physiological condition of the crop and its resistance to late blight, this paper addresses the question whether crop physiology can help to combat the disease. Although there are possibilities to (partly) escape to the late blight by advancing the crop cycle or the tuber bulking, it is concluded that crop physiology can do little to reliably reduce the susceptibility to late blight. Breeding for resistance remains the best option.

Late blight is a devastating disease in potato production world-wide. Breeding for resistance is complex because of the versatile and aggressive population of Phytophthora infestans, which overcomes any new genetic source of resistance very rapidly. There are reliable fungicides available to control the disease, but chemical control is costly and harmful to the environment. There are no cultural practices reducing the infestation, which are reliable enough to cope with the disease in a non-chemical way. Given the close link between the physiological condition of the crop and its resistance to late blight, this paper addresses the question whether crop physiology can help to combat the disease. Although there are possibilities to (partly) escape to the late blight by advancing the crop cycle or the tuber bulking, it is concluded that crop physiology can do little to reliably reduce the susceptibility to late blight. Breeding for resistance remains the best option.

The destructive plant disease potato late blight is caused by the oomycete pathogen Phytophthora infestans (Mont.) de Bary. This disease has remained particularly problematic despite intensive breeding efforts to integrate resistance into cultivated potato, largely because of the pathogen's ability to quickly evolve to overcome major resistance genes. The RB gene, identified in the wild potato species S. bulbocastanum , encodes a protein that confers broad-spectrum resistance to most P. infestans isolates through its recognition of highly conserved members of the corresponding pathogen effector family IPI-O. IpiO is a multigene family of effectors and while the majority of IPI-O proteins are recognized by RB to elicit host resistance, some variants exist that are able to elude detection (e.g. IPI-O4). In the present study, analysis of ipiO variants among 40 different P. infestans isolates collected from Guatemala, Thailand, and the United States revealed a high degree of complexity within this gene family. Isolate aggressiveness was correlated with increased ipiO diversity and especially the presence of the ipiO4 variant. Furthermore, isolates expressing IPI-O4 overcame RB-mediated resistance in transgenic potato plants even when the resistance-eliciting IPI-O1 variant was present. In support of this finding, we observed that expression of IPI-O4 via Agrobacterium blocked recognition of IPI-O1, leading to inactivation of RB-mediated programmed cell death in Nicotiana benthamiana . In this study we definitively demonstrate and provide the first evidence that P. infestans can defeat an R protein through inhibition of recognition of the corresponding effector protein.

Spongospora subteranea, the causal agent of potato powdery scab is becoming increasingly important worldwide. Little is known about the genetic basis of resistance to this disease. The present study tested the hypothesis that potato genotypes with stable genetic resistance to “Spongospora root galling” were present in potato germplasm. Root galling index values of 24 genotypes screened for resistance in four field trials (environments) in 2004 and 2005 in Washington State and Idaho were analyzed. Genotypes tested included five resistant, four industry standards and advanced selections from the USDA-ARS, Prosser, WA program. Broad-sense heritability was calculated as 0.76 with a 95% confidence interval of 0.55–0.89, indicating a fairly high genetic component of the trait. Of the 24 genotypes that were tested, eight showed no genotype*environment interactions while six of the remainder had significant variance (i.e., they were unstable) after removal of genotype*environment variance. Among the five resistant genotypes, PA95B2-4 was stable, and PA98N5-2, PA98NM38-1, PO94A009-7 and POR00HG5-1 were stable after the removal of environmental heterogeneity. Among the four industry standards, Shepody was unstable, whereas Ranger Russet, Russet Burbank and Umatilla Russet were stable after the removal of genotype*environment variance. Stable resistance to “Spongospora root galling” was identified. A large portion of the variation was genetic, which will enable breeders to use resistant and stable potato genotypes as parents in future breeding to develop superior commercial potato cultivars with resistance to “Spongospora root galling”.

Potato is consumed worldwide and represents the fourth most important staple food crop after rice and wheat. Potato cultivars display a large variety of color, shape, taste, cooking properties and starch content but are all derived from the same species; Solanum tuberosum. Potato breeding is an economic important activity for international breeding companies, but also plays an important role in breaking the circle of poverty for small farmers. In the Andean region, most farmers use many different potato genotypes combined with farming practices transmitted orally over thousands of years. The most prominent menace to potato production is Late Blight caused by the oomycete Phytophthora infestans which destroys leaves, stems and tubers. Differences of breeding methods between the potato grown in South America and in the rest of the world is related to differences in the consequences of Late Blight infection. In the 19th, century, entire potato fields in Ireland were devastated while in South America P. infestans proliferation was readily inhibited. This difference is found in the biodiversity reserve such as that of the Chiloé archipelago in Chile where local people cultivate about 200 varieties of native potato. Obviously, the genetic diversity of cultivated native potato acts as a shield against this versatile pathogen. Inspired by this model to solve the problems raised by the extensive use of potato monoculture, growers and breeders need to maintain genetic diversity in the European staple food crops. In exploring the South American native potato collection, Solanum demissum and later on Solanum bulbocastanum appeared to be a source of resistance genes (Rpi) to P. infestans. The S. demissum Rpi genes were transmitted to potato breeding clones by traditional introgression breeding. However the fading of their ability in providing effective resistance against Late Blight infection was witnessed within a decade. In the pursuit to provide a hopefully more durable protection in existing potato cultivars, plant breeding scientists proposed to directly introduce South American native potato Rpi genes in modern potato varieties by using a so-called cisgenic approach. This in contrast to transgenic plants which can contain genes which have originated from non related genera or even different kingdoms. Breeding of cisgenic plants is on its way to public acceptance because of its inherent resemblance to natural crossing and because efforts are made by the scientific community to explain the principles of cisgenesis. Lessons were learned from the flexibility of P. infestans to overcome the effect of newly introduced Rpi genes and, therefore, efforts are still ongoing to discover and clone new Rpi genes from native potatoes. With this in mind, a new family of Rpi genes represented by Rpi-blb3, Rpi-abpt, R2, R2-like and Rpi-mcd1.1 were characterized in clones derived from S. bulbocastanum, S. demissum, S. edinense and S. microdontum. We accomplished in this research the physical isolation of these genes, the molecular characterization of their functionality and the allelic distribution in the Petota collection. Rpi-blb3, Rpi-abpt, R2, R2-like and Rpi-mcd1.1 belong to the potato linkage group IV and all contain signature sequences characteristic of LZ-NBS-LRR proteins. The closest known R gene so far is RPP13 from Arabidopsis thaliana which shares an amino-acid sequence similarity of 35%. The LRR domains of Rpi-blb3, Rpi-abpt, R2 and R2-like proteins are highly homologous, whilst LZ and NBS domains are more polymorphic with those of R2 being the most divergent. All four Rpi genes recognize the recently identified RXLR effector protein PiAVR2 which is secreted by P.infestans in the cytoplasm of plant cells during the infection process. Unlike Rpi-blb3, Rpi-abpt, R2 and R2-like , the S. microdontum resistance gene Rpi-mcd1.1 does not interact with PiAVR2 and provides a different resistance spectrum. Rpi-mcd1.1 shares 90% nucleotide identity with Rpi-blb3 and polymorphic nucleotides are mainly located in the LRR region. The S. bulbocastanum haplotypes of Rpi-blb1, Rpi-blb2 and Rpi-blb3 were discovered in several Mexican diploid as well as polyploid species closely related to S. bulbocastanum. These three resistance genes occurred in different combinations and frequencies in S. bulbocastanum accessions and their distribution is confined to Central America. A selected set of genotypes was tested for their response to the avirulence effectors IPIO-2, Avr-blb2 and Pi-Avr2, which interact with Rpi-blb1, Rpi-blb2 and Rpi-blb3, respectively, as well as by disease assays with a diverse set of isolates. Using this approach some accessions could be identified that contain novel, yet unknown, Late Blight resistance factors in addition to the Rpi-blb1, Rpi-blb2 and Rpi-blb3 genes Analysis of the sequences obtained in different allele mining strategies suggests an evolution of the major late blight locus on linkage group IV through recombination and point mutations. By making use of the sequence information provided by the alleles, we identified the repeats and amino acids in the LRR domain which are specific for PiAVR2 recognition. Finally, we discussed the results described in this thesis in a potato/ P. infestans co-evolution context.

Late blight caused by Phytophthora infestans is historically a serious epidemic disease in potato and tomato cultivations. Accession L3708 (Solanum pimpinellifolium), a new source for late blight resistance was identified in AVRDC, and carries the resistance gene, Ph-3, incompatible to P. infestans race 3. The AFLP markers linked to Ph-3 were previously developed from the L3708 accession (Chunwongse et al. 2002). To facilitate tomato breeding with the Ph-3 gene, an attempt was made to convert AFLP markers to sequence-characterized amplified region (SCAR) markers. Among 6 AFLP markers, only one AFLP marker, L87, was successfully converted to SCAR marker. The resistance-specific 230 bp AFLP fragment was cloned and sequenced, and the PCR primer amplifying a 123 bp fragment was designed. This SCAR marker could discriminate resistant and susceptible individuals with high stringency. The developed SCAR marker could be used for the marker assisted-selection in tomato breeding programs.

Common scab (CS), caused by Streptomyces spp., is a soil-borne bacterial disease of potato tubers which may cause superficial, raised, or pitted lesions. The results of screening potato germplasm for severity of CS can be variable, necessitating testing over multiple environments. The purposes of this study were to evaluate advanced germplasm from public potato breeding programs in different regions of the United States for their reaction to CS, estimate broad-sense heritability for resistance, and identify clones with stable resistance. Seventeen to 23 clones per year were evaluated at each of three locations (ID, ME, MN) from 2002 to 2007. After harvest, each tuber was scored for the percent of surface area covered with lesions and the type of lesion. These scores were converted to an area index (AI) and a lesion index (LI). AI, LI, and the arcsine √ proportion scabby tubers (PS) were analyzed as normally distributed responses. There were significant differences among clones for AI in 2 years, LI in 5 years, and PS in 3 years. There were significant clone x location interactions for AI and PS all 6 years, and LI in 5 years. Broad-sense heritability for AI, LI, and PS ranged from 0 to 0.78, 0.49 to 0.90, and 0.30 to 0.80, respectively. Evaluation at multiple sites remains important for characterizing the reaction of potato germplasm to CS.

Potato (Solanum tuberosum L.) is nowadays the most important non-cereal food crop in the world. It is prone to huge annual losses due to late blight, the disease caused by the oomycete pathogen Phytophthora infestans. Modern management of late blight necessitates the use of multiple resistance (R) genes, which requires efficient pipelines for identification, isolation and characterization of R genes. This thesis employs effectoromics, i.e. the use of effectors (pathogenic secreted protein) to probe corresponding R gene(s) in a host plant and sort out their functional redundancy and specificity. Using cytoplasmic RXLR effectors of P. infestans to probe resistant Solanum germplasm for late blight R genes, we were able to: (i) assess the biodiversity of Avr-blb1, characterize the genomic structure of virulent P. infestans isolates on Rpi-blb1 plants and thus provide a technical solution for long-term disease management; (ii) identify the centre of origin of R3a, characterize R3a gene homologues and a functional R gene (Rpi-sto2), and (iii) uncover the potential co-evolution at both R and Avr side for the R2/PiAvr2-PexRD11 interactions, providing more diversity and specificity of R2 homologues, which may be valuable for potato breeding