Potato (Solanum tuberosum L.) genotypes with relatively high yield level and resistance to the late blight disease are being developed by the International Potato Centre (CIP) and made available to developing countries. However, for effective breeding for high yield and late blight resistance, these CIP materials and locally adapted genotypes need to be evaluated and screened under target growing environmental conditions. The objectives of the study were to determine yield response and late blight resistance of potato genotypes grown in Rwanda and candidate clones obtained from CIP and to identify suitable parents for breeding. A total of 44 potato genotypes, 30 acquired from CIP and 14 local varieties were evaluated under three environments (Kinigi, Rwerere and Nyamagabe). Experiments were laid out in an 11 × 4 alpha lattice design with two replications. Data were collected on late blight severity (%) based on the relative area under the disease progress curve (RAUDPC: 100 % max), total tuber yield, marketable tuber weight and dry matter content. Genotypes had significant differences on blight resistance and yield levels among test locations. Eight genotypes (391,047.34, 393,385.39, 393,280.82, 396,036.201, Gikungu, Ngunda, Kigega and Nderera) were identified as promising parents for subsequent crosses. The selected genotypes display farmers-preferred traits, productive flowers, high to medium late blight resistance and high yields.

Noncommercial varieties of potatoes (Solanum tuberosum L.) harbor genetic potential for improvements of disease resistance and abiotic stress tolerance in commercial potato cultivars; however, introducing traits from noncommercial varieties to breeding stock can be extremely labor intensive. Molecular genetic markers closely associated with a trait can be used to decrease the time spent phenotyping varieties. Here we review genetic markers that have been used for marker-assisted selection (MAS) in potato. Most MAS markers have been used to detect disease resistance genes, and our review focuses on those markers. Complex traits such as cold, drought and viral tolerance can be studied by comparing expressed genes; next-generation sequencing technologies will help in the discovery of trait-specific molecular markers. This review aids in summarizing the potential of these molecular tools when breeding for complex traits in potato.

In the Canary Islands, a number of old Andean potato introductions have been maintained by farmers and are cultivated there since the sixteenth century. Genetic resistance is an inexpensive way to control the main pests and diseases of potato and avoids the use of phytochemicals or other costly protective measures. In this study, we have analysed eight Solanum tuberosum subsp. andigena and S. tuberosum subsp. tuberosum accessions, representing old potato varieties from Tenerife Island, for their resistance levels to Phytophthora infestans, Globodera rostochiensis, Globodera pallida and Pectobacterium atrosepticum. New resistance sources against P. infestans in leaves and P. atrosepticum were found, as well as partial resistance to both nematode species. The results suggest the potential exploitation of the cultivar Venezolana Negra in breeding programmes in order to improve pest and disease resistance of potato.

Under organic farming conditions late blight, caused by Phythophtora infestans, poses one of the highest production risks. Extensive plant breeding activities are needed to offer varieties which show higher resistance to this potato disease. For organic farming cultivars are required to thrive under reduced pest management and increased mechanical stress. To meet these demands the German Federal Ministry of Food and Agriculture has promoted a joint research project funded through the “Federal Organic Farming Scheme and other forms of sustainable agriculture” (BÖLN). The project brings together the German expertise in potato breeding: the Julius Kühn–Institut (JKI), the Leibniz-Institut für Pflanzengenetik und Kulturpflanzenforschung (IPK), the Bayerische Landesanstalt für Landwirtschaft (LfL) and German potato breeding companies. A variety of modern and historic cultivars from potato breeders and the IPK Genbank, respectively, were used to combine quality traits with the late blight resistance of JKI breeding clones and other selected clones. Phenotypic results from a variety trial were used to choose suitable breeding partners. Where possible, the progeny were preselected using genetic markers for virus, nematode and late blight resistance. Central aspect of the project was to select clones in field trials under organic farming conditions. Since 2012 scientists and organic farmers have been choosing jointly from more than 2000 individuals per year to establish a late blight breeding pool for organic farming.

K. Park et al., 'Evaluation of late blight resistance and agronomic characteristics for B3C1 clones and its segregating progenies under long-day conditions in Korea', American Journal of Potato Research, 2015 | Potato late blight caused by the fungus Phytophthora infestans is the most important disease in the world. Developing potatoes resistant to late blight is a major breeding effort around the world. International Potato Center (CIP) developed a potato population with durable resistance to late blight. These clones (B3C1) were bred in Peru under short-day conditions, growing in long-day conditions such as Korea is not feasible. The purpose of this study was to evaluate late blight resistance and major agronomic characteristics of CIP?s breeding lines, and agronomic potential of segregating progeny from B3C1 under long-day conditions in Korea. Late blight resistance of B3C1 clones was evaluated in naturally infested fields. AUDPC (Area Under Disease Progress Curve) values of all B3C1 clones were significantly lower than those of control varieties Atlantic and Haryeong, indicating B3C1 clones have high levels of resistance. However, most of the B3C1 clones had lower tuber yield compared to control cultivars, presumably due to differences in adaptability to long-day conditions. Two clones, 381580.30 and 392635.54 were susceptible to common scab (Streptomyces scabies) and 384398.56 and 393382.44 had a high percentage of tuber disorders. Four clones, including 391047-34, had relatively high marketable yield, high specific gravity, and desirable agronomic characteristics. To develop clones highly resistant to late blight and with good adaptability in long-day condition, B3C1 clones were crossed with Korean breeding lines. Through individual selection for several years, 25 clones were selected as promising lines with good agronomic characteristics and high resistance to late blight

Potato late blight, caused by the oomycete phytopathogen Phytophthora infestans, is a devastating disease found in potato-growing regions worldwide. Long-term management strategies to control late blight include the incorporation of host resistance to predominant strains. However, due to rapid genetic changes within pathogen populations, rapid and recurring identification and integration of novel host resistance traits is necessary. Wild relatives of potato offer a rich source of desirable traits, including late blight resistance, but screening methods can be time intensive. We tested the ability of taxonomy, ploidy, crossing group, breeding system, and geography to predict the presence of foliar and tuber late blight resistance in wild Solanum spp. Significant variation for resistance to both tuber and foliar late blight was found within and among species but there was no discernable predictive power based on taxonomic series, clade, ploidy, breeding system, elevation, or geographic location. We observed a moderate but significant correlation between tuber and foliar resistance within species. Although previously uncharacterized sources of both foliar and tuber resistance were identified, our study does not support an assumption that taxonomic or geographic data can be used to predict sources of late blight resistance in wild Solanum spp.

Background The soil borne, obligate biotrophic fungus Synchytrium endobioticum causes tumor-like tissue proliferation (wart) in potato tubers and thereby considerable crop damage. Chemical control is not effective and unfriendly to the environment. S. endobioticum is therefore a quarantined pathogen. The emergence of new pathotypes of the fungus aggravate this agricultural problem. The best control of wart disease is the cultivation of resistant varieties. Phenotypic screening for resistant cultivars is however time, labor and material intensive. Breeding for resistance would therefore greatly benefit from diagnostic DNA markers that can be applied early in the breeding cycle. The prerequisite for the development of diagnostic DNA markers is the genetic dissection of the factors that control resistance to S. endobioticum in various genetic backgrounds of potato. Results Progeny of a cross between a wart resistant and a susceptible tetraploid breeding clone was evaluated for resistance to S. endobioticum pathotypes 1, 2, 6 and 18 most relevant in Europe. The same progeny was genotyped with 195 microsatellite and 8303 single nucleotide polymorphism (SNP) markers. Linkage analysis identified the multi-allelic locus Sen1/RSe-XIa on potato chromosome XI as major factor for resistance to all four S. endobioticum pathotypes. Six additional, independent modifier loci had smaller effects on wart resistance. Combinations of markers linked to Sen1/RSe-XIa resistance alleles with one to two additional markers were sufficient for obtaining high levels of resistance to S. endobioticum pathotypes 1, 2, 6 and 18 in the analyzed genetic background. Conclusions Potato resistance to S. endobioticum is oligogenic with one major and several minor resistance loci. It is composed of multiple alleles for resistance and susceptibility that originate from multiple sources. The genetics of resistance to S. endobioticum varies therefore between different genetic backgrounds. The DNA markers described in this paper are the starting point for pedigree based selection of cultivars with high levels of resistance to S. endobioticum pathotypes 1, 2, 6 and 18.

Host resistance to late blight was of significance in integrated late blight management due to its longterm economic benefits for small-scale farmers. It also minimized changes in the population structure of Phytophthora infestans, decreasing the likelihood of fungicide resistance. In this regards Conventional breeding efforts have produced more than a dozen late blight resistant varieties, which have been deployed throughout the country. Again, the use of chemical fungicides had resulted in an increased degree of pathogen resistance. Sensitivity of P. infestans to Metalaxyl was monitored on potato leaf disks, detached leaves, or whole plants. The continuous changes in P. infestans populations required careful adaptation of successful disease management programmes. Combination of cultivar resistance and regular applications of protective fungicides were reported to reduce foliar late blight infection in potato. Also Modern approaches in chemical control emphasized on reducing fungicide inputs, combined with using potato cultivars possessing acceptable levels of non-race specific resistance to late blight.

The mission of International Potato Centre (CIP) is to achieve food security for developing countries. Late blight is one of the most serious diseases of potato, and efficient control of the disease is needed to get proper yield. Chemical plant protection and resistant cultivars are the main keys in controlling late blight. CIP improves the food security by breeding late blight resistant genotypes, which are further tested in developing countries. In this research CIP’s breeding population B3 was studied for the inheritance and stability of late blight resistance. Inheritance of resistance was analysed by comparing the level of resistance in two consecutive cycles of recurrent selection (C2 and C3). The stability of resistance was analysed by comparing historical data of population B3 in nine different environments in years 2001–2006. Results showed that the fourth cycle of recombination will improve late blight resistance in the population and the resistance is mainly caused by genetic factors. The research also revealed 78 genotypes that had stable late blight resistance in studied environments. In addition, the study suggests that the population contains some still unidentified R genes. Population B3 has already high late blight resistance, which the fourth cycle of recombination will further improve. In addition, the population contains genotypes with stable and extremely high late blight resistance. Thus, the population serves as a strong material for further late blight resistance breeding and as trial genotypes for tropical highlands. However, the still unidentified R genes should be studied further at molecular level to get best out of the population.

M. Mwathi et al., 'Genetic transformatin of potato with a triple R gene construct to confer resistance to late blight', 2015 | The cultivated potato, Solanum tuberosum is affected by a variety of diseases with late blight (LB) caused by Phytophthora infestans being the most severe. The disease is mostly controlled by the application of large quantities of fungicides, which represent a financial burden on farmers indeveloping countries and pose risks to both human health and the environment. A more effective and environmentally friendly strategy to prevent damages caused by P. infestans is to use resistant potato cultivars. In the early days of breeding for LB resistance, a small number of resistance (R) genes from the wild Mexican species, Solanum demissum, were introgressed into modern potato varieties. These genes conferred race-specific resistance, which was rapidly overcome by new isolates of the pathogen. Recently, a number of new R genes have been identified and cloned from several wild potato species .Taking advantage of genetic engineering, our strategy is to use three of these new R genes (RB, Rpiblb2 and Rpi-vnt1.1) in a triple gene construct, p CIP 99, based on the hypothesis that simultaneous mutation for pathogenicity against all three genes is unlikely, and therefore the resistance conferred by the construct should be durable. We plan to deploy the three stacked R genes into the potato variety ?Victoria? (known in Kenya and Uganda as ?Asante?). To date, we have produced more than 100 transgenic events which are currently being characterized. The pathogen population will be characterized concurrently to assess the expected durability of this resistance