Genetic diversity is considered as man's best protection against food insecurity since it makes available the characters that could counteract threats to food production such as pest and adverse environmental conditions. However, genetic diversity in crops could decrease and even be lost by the replacement of landraces or native varieties which have high variability with those developed through breeding. In sweet potato, active breeding programs have been pursued by several research institutions in the Philippines in the last 30 years, resulting in 29 varieties approved for commercial production by the National Seed Industry Council (NSIC, formerly the Philippine Seed Board) as of 2005. These varieties yield at least twice higher than the traditional ones and will, thus, definitely increase sweet potato production in the country if these varieties are grown. The study analyzed the variability in 23 of the improved sweet potato varieties in the Philippines to determine if replacement of landraces by modern sweet potato varieties would be a threat to the existing genetic variation in the crop in the country. Variability was measured on the basis of 31 characters, 26 of which were qualitative. High diversity/variability was shown by the 23 varieties in 23 of 26 qualitative traits and all five quantitative characters in terms of the number of phenotypic classes exhibited as well as the values of the Shannon-Weaver diversity index, which averaged 0.70. The average Gower Similarity coefficients among variables were low, especially if only qualitative or highly genetically controlled traits were considered, an average of 0.37 among the 23 varieties and 0.28 among the three more popular ones. Thus, even if these modern varieties were planted in most of the sweet potato growing areas in the country, sufficient variability in the crop will still exist, at leased based on the characters studied. A more complete assessment of genetic diversity in the Philippine modern sweet potato cultivars by using other methods of variability is therefore recommended.

International audience | Fourteen microsatellite loci were isolated and characterized in the potato aphid, Macrosiphum euphorbiae Thomas, by screening a genomic library with the oligonucleotide probes (GA)(10) (GT)(10) and (GATA)(4). Allelic diversity was estimated in samples collected from potato fields in Tunisia. Ten loci displayed polymorphism that ranged from two to four alleles per locus and the observed heterozygosity ranged from zero to one. These markers could be used to study the population genetic structure of this polyphagous aphid species.

Fourteen microsatellite loci were isolated and characterized in the potato aphid, Macrosiphum euphorbiae Thomas, by screening a genomic library with the oligonucleotide probes (GA)(10) (GT)(10) and (GATA)(4). Allelic diversity was estimated in samples collected from potato fields in Tunisia. Ten loci displayed polymorphism that ranged from two to four alleles per locus and the observed heterozygosity ranged from zero to one. These markers could be used to study the population genetic structure of this polyphagous aphid species.

In order to determine the genetic diversity of Phytophthora infestans in Costa Rica, a total of 62 isolates were collected in potato-growing regions of Cartago, Zarcero, Heredia and Fraijanes during 1999-2001 and subjected to a RAPD analysis. All isolates were previously assayed for mating type and meta laxyl resistance. By using 11 primers, it was possible to generate 17 RAPD genotypes, with frequencies ranging from 0.55 to 0.02. Resistant and susceptible isolates coming from all sampled zones were found in the most frequent group. All isolates from the 17 groups showed a genetic relationship. The highest genetic variation was found among isolates; therefore, the population structure was not fractioned as a result of the production zone or the sensitivity to metalaxyl. Analyses with the Gst coefficient showed no genetic similarities between Costa Rican and the foreign (US-1, US-18, and EC-1) isolates. In conclusion, RAPD analysis revealed the genetic diversity of the P. infestans population in Costa Rican potato fields, although there is a possibility that all isolates are sharing a common ancestor. | Para determinar la diversidad genética de Phytophthora infestans en Costa Rica, 62 aislamientos de este patógeno fueron recolectados en plantaciones de papa en las zonas de Cartago, Zarcero, Fraijanes y Heredia durante 1999-2001 y analizados con el uso de RAPDs. Todos los aislamientos fueron previamente evaluados para el tipo de apareamiento y la resistencia al metalaxyl. Se seleccionó 11 imprimadores con los cuales fue posible formar 17 grupos RAPD cuyas frecuencias variaron de 0,55 a 0,02. En el grupo más frecuente se encontró aislamientos resistentes y sensibles provenientes de todas las zonas muestreadas. Todos los aislamientos en los 17 grupos mostraron una alta relación genética. La mayor diversidad genética se encontró entre aislamientos y no se observó ninguna sub-estructuración poblacional de acuerdo a las zonas o sensibilidad al metalaxyl. Al comparar los aislamientos costarricenses con los aislamientos foráneos US-1, US-18 y EC-1, no se observó ninguna relación genética entre ambas poblaciones; de hecho, el coeficiente de diferenciación genética Gst mostró que la población local es diferente a la de los aislamientos foráneos. El análisis con los RAPDs reveló que la población de P. infestans, en las plantaciones de papa en Costa Rica, es diversa aunque probablemente los aislamientos comparten un ancestro en común.

We have generated estimates of the genomic distribution of newly developed molecular markers, which are P450-based analogues (PBAs), in diploid potato (Solarium tuberosum, 2n = 2x = 24) based on functional genomics. A total of 401 markers, including 111 SSR, 33 RFLP, 87 RFLP-STS, 45 CAPS, 94 RAPD, 15 PBA, 9 AFLP, 3 RGL and 4 ISSR markers, were employed in a parental polymorphism survey. A total of 127 out of 401 markers (172 loci) displayed polymorphisms between parents and were confirmed to show segregation in partial progenies. These selected 127 markers were then tested for their possible use for a whole mapping population. The subsequent results of genetic mapping of the PBAs revealed that they were distributed on at least 8 chromosomes, suggesting that they have a significant potential not only as tools for assessing genetic diversity but also as effective markers to construct more detailed genetic maps of potato, in conjunction with existing identified genetic loci. To integrate the information from existing maps into our mapping study, we performed a comparative analysis between two representative maps (RFLP and SSR-based) with our PBA map. Based on the subsequent results, we predict that our map will be useful as a bridge between the existing genetic maps of potato and will enable to integrate information about different markers.

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Pink rot of potato (Solanum tuberosum), caused by Phytophthora erythroseptica, is found wherever potatoes are grown, and in the last decade, it has reemerged as an economically important disease in Canada and the United States. A selection of isolates of P. erythroseptica from major potato-growing regions in North America, namely Prince Edward Island and New Brunswick, Canada, and Maine and Idaho, U.S.A., was assessed for genetic diversity with randomly chosen decanucleotide primers which were used to amplify regions of DNA to reveal polymorphisms among templates (random amplified polymorphic DNA [RAPD]). The isolates varied in their geographic origin as well as in their sensitivity to mefenoxam, as determined by an in vitro assay. In three separate RAPD screens (I, II, and III) with 23 isolates of P. erythroseptica chosen from a larger collection, 1,410, 369, and 316 robust, scorable bands were amplified, respectively. However, among the bands amplified in screens I, II, and III, only 3, 1, and 3 bands, respectively, were polymorphic. When three primers yielding polymorphisms were used to screen 106 isolates from Prince Edward Island and New Brunswick, or a representative collection of 32 isolates from Prince Edward Island, New Brunswick, Maine, and Idaho, no major variation was discovered. RAPD markers were not correlated with geographic origin or mefenoxam sensitivity of the isolates. From an evolutionary standpoint, the absence of genetic diversity among the isolates of P. erythroseptica we examined may be attributable to the relatively recent introduction of a small founding population of the pathogen in North America.

The central highlands of Mexico are considered to be a center of genetic diversity for both the potato late blight pathogen and for tuber-bearing Solanum spp. Recent work conducted in Mexico and South America sheds new light on the biology and evolution of Phytophthora infestans and other related Phytophthora pathogens. It now appears that Mexican Solanum species, which coevolved with P. infestans and were previously known for providing a source of R-genes, also provide a source of quantitative, rate-reducing resistance that is highly effective, stable, and durable. It is now apparent that Mexico is the center of origin not only of the potato late blight pathogen P. infestans, but also of several related Phytophthora species including P. mirabilis, P. ipomoeae, and possibly P. phaseoli. We close with the hypothesis that these Phytophthora species evolved sympatrically from one ancestral host through adaptive radiation onto their respective four host families.

The cultivated potato, Solanum tuberosum, ultimately traces its origin to Andean and Chilean landraces developed by pre-Colombian cultivators. These Andean landraces exhibit tremendous morphological and genetic diversity, and are distributed throughout the Andes, from western Venezuela to northern Argentina, and in southern Chile. The wild species progenitors of these landraces have long been in dispute, but all hypotheses center on a group of 20 morphologically very similar tuber-bearing (Solanum section Petota) wild taxa referred to as the S. brevicaule complex, distributed from central Peru to northern Argentina. We present phylogenetic analyses based on the representative cladistic diversity of 362 individual wild (261) and landrace (98) members of potato (all tuber-bearing) and three outgroup non-tuber-bearing members of Solanum section Etuberosum, genotyped with 438 robust amplified fragment length polymorphisms. Our analyses are consistent with a hypothesis of a "northern" (Peru) and "southern" (Bolivia and Argentina) cladistic split for members of the S. brevicaule complex, and with the need for considerable reduction of species in the complex. In contrast to all prior hypotheses, our data support a monophyletic origin of the landrace cultivars from the northern component of this complex in Peru, rather than from multiple independent origins from various northern and southern members.