Late blight is the most devastating disease of the potato crop that can be effectively managed by growing resistant cultivars. Introgression of resistance (R) genes/quantitative trait loci (QTLs) from the Solanum germplasm into common potato is one of the plausible approaches to breed resistant cultivars. Although the conventional method of breeding will continue to play a primary role in potato improvement, molecular marker technology is becoming one of its integral components. To achieve rapid success, from the past to recent years, several R genes/QTLs that originated from wild/cultivated Solanum species were mapped on the potato genome and a few genes were cloned using molecular approaches. As a result, molecular markers closely linked to resistance genes or QTLs offer a quicker potato breeding option through marker-assisted selection (MAS). However, limited progress has been achieved so far through MAS in potato breeding. In near future, new resistance genes/QTLs are expected to be discovered from wild Solanum gene pools and linked molecular markers would be available for MAS. This article presents an update on the development of molecular markers linked to late blight resistance genes or QTLs by utilization of Solanum species for MAS in potato.Key words: late blight -molecular marker -MAS -potato -resistance gene -Solanum species Late blight caused by the oomycete (Phytophthora infestans (Mont.) de Bary) is the most important disease of potato production worldwide. This disease caused devastating impact on humanity in the mid-1840s when severe epidemics swept through Europe and resulted in the Irish potato famine (Fry 2008). Consequently, given its significant importance, there have been concerted global efforts for more than 100 years to develop durable resistant potato cultivars against P. infestans. However, evolution of new races of P. infestans was able to conquer the past resistance genes and resulted in susceptible cultivars worldwide. Durably resistant cultivars against a range of P. infestans isolates possessing multiple resistance genes are needed today, which can be developed in less time by conventional and molecular approaches. Regardless of the fact that common potato lacks significant sources of resistance, many wild Solanum species are rich sources of resistance genes. Globally breeders exploited only a very limited scale of Solanum biodiversity in potato breeding. For example, the genetic base of modern Indian potato cultivars is limited to 49 ancestors only involving the wild species S. rybinii and S. demissum. Late blight resistance genes were introgressed from the wild species S. demissum, S. stoloniferum and the cultivated S. tuberosum subsp. andigena and S. phureja into common potato in different parts of the world (Bradshaw et al. 2006c). Thus, it necessitates potato breeders to search for new sources of resistance in wild gene pools and their faster deployment into cultivars through markerassisted selection (MAS).Conventional breeding methods are of primary importance but ar...

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The genetic stability of in vitro propagated potato microtubers was assessed using random amplified polymorphic DNA (RAPD), inter simple sequence repeat (ISSR), simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers. Microtubers were developed through in vitro from potato microplants using standardized protocols. The microtubers were conserved for 1 year under three different culture media and consequently microplants were regenerated for the DNA analyses. During the study, a total of 38 (10 RAPD, 11 ISSR, 12 SSR and 5 AFLP) primers produced a total of 407 (58 RAPD, 56 ISSR, 96 SSR and 197 AFLP) clear, distinct and reproducible amplicons. Cluster analysis revealed 100 % genetic similarity among the mother plant and its derivatives within the clusters by SSR, ISSR and RAPD analyses, whereas AFLP analysis revealed from 85 to 100 % genetic similarity. Dendrogram analysis based on the Jaccard's coefficient classified the genotypes into five clusters (I-V), each cluster consisting of mother plant and its derivatives. Principal component analysis (PCA) also plotted mother plant and its genotypes of each cluster together. Based on our results, it is concluded that AFLP is the best method followed by SSR, ISSR and RAPD to detect genetic stability of in vitro conserved potato microtubers. The in vitro conservation medium (T2) is a safe method for conservation of potato microtubers to produce true-to-type plans.

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Background: Genetic and epigenetic changes (DNA methylation) were examined in the tissue-culture propagated interspecific potato somatic hybrids between dihaploid Solanum tuberosum and S. pinnatisectum. Amplified fragment length polymorphism (AFLP) and methylation-sensitive amplified polymorphism (MSAP) were applied to detect the genetic and epigenetic changes, respectively in the somatic hybrids mother plants (1 st cycle) and their regenerants (30 th cycles sub-cultured). Results: To detect genetic changes, eight AFLP primer combinations yielded a total of 329 scorable bands of which 49 bands were polymorphic in both mother plants and regenerants. None of the scorable bands were observed in term of loss of original band of mother plant or gain of novel band in their regenerants. AFLP profiles and their cluster analysis based on the Jaccard's similarity coefficient revealed 100% genetic similarity among the mother plant and their regenerants. On the other hand, to analyze epigenetic changes, eight MSAP primer pair combinations detected a few DNA methylation patterns in the mother plants (0 to 3.4%) and their regenerants (3.2 to 8.5%). Out of total 2320 MSAP sites in the mother plants, 2287 (98.6%) unmethylated, 21 (0.9%) fully methylated and 12 (0.5%) hemimethylated, and out of total 2494 MSAP sites in their regenerants, 2357 (94.5%) unmethylated, 79 (3.1%) fully methylated and 58 (2.3%) hemi-methylated sites were amplified. Conclusion: The study concluded that no genetic variations were observed among the somatic hybrids mother plants and their regenerants by eight AFLP markers. However, minimum epigenetic variations among the samples were detected ranged from 0 to 3.4% (mother plants) and 3.2 to 8.5% (regenerants) during the tissue culture process.