R. Ortiz, 'The state of use of potato genetic diversity', pp.181-200, 2001

These proceedings have been compiled and edited based on the papers presentedat this workshop, dealing with objectives as set by ANSWER members. They contain the information on the progress made during the three years since the members met last time, but more importantly they record the commitments made by different partners for furthering sweetpotato genetic resources work in Asia. They also contain the recommendations on strategies and approaches proposed at the workshop, which will form the basis for future work of ANSWER. It is my hope that the publication and distribution of this volume will stimulate further the already vigorous activity in sweetpotato genetic resources conservation and use in the region | V. Ramanatha Rao, M. (eds.) Hermann, 'Conservation and utilization of sweet potato genetic diversity in Asia', p.73, 2001

The goal of germplasm conservation in genebanks is to maximize genetic variation. Collecting explorations would be more efficient if factors that predict areas and habitats associated with greater genetic differences and diversity could be identified. Therefore, the objective of this research was to investigate whether ecogeographical variables have significant associations with patterns of genetic variation in wild potato populations. This study examined 96 wild potato populations collected from the southwestern USA. These were 43 populations of Solanum fendleri (2n = 4x = 48) and 53 populations of S. jamesii (2n = 2x = 24). These species represent two of the most predominant breeding systems found among Solanum species: tetraploid inbreeders and diploid outcrossers, respectively. Random amplified polymorphic DNA (RAPD) markers were used to assess populations in two ways: determination of simple genetic difference between pairs of populations, and genetic diversity of a population based on the frequency of that population's RAPD markers in the whole set. Results from 2282 comparisons indicated that patterns of genetic differences were not associated with any differences in ecogeographical structure assessed. Remarkably, even geographical separation of populations, a parameter usually considered important when collecting germplasm, did not predict genetic differences very well. Latitude, longitude, and heat-related factors significantly predicted genetic diversity in S. fendleri but not in S. jamesii This experiment revealed few associations between ecogeographic parameters and genetic variation in the wild. It follows, therefore, that one should collect many populations and incorporate a manageable subset into the genebank on the basis of empirical measurements of genetic diversity.

The RAPD procedure and SSRs analysis were used to study genetic diversity of 30 potato (Solanum tuberosum) genotypes, representing mainly Czech potato cultivars. Amplification with six decamer RAPD primers generated 66 DNA fragments, ranging in size from 178 bp to 1847 bp, of which 46 were polymorphic products. Twenty-two primer pairs flanking simple sequence repeats (SSRs) were examined for their potential use in DNA fingerprinting of potato. Total of 76 bands of sizes ranging from 98 to 500 bp were amplified, 56 bands were polymorphic. Similar matrixs derived from fourteen SSRs and six RAPD were able to distinguish selected cultivars. The utilisation of both approaches is discussed.

These proceedings have been compiled and edited based on the papers presentedat this workshop, dealing with objectives as set by ANSWER members. They contain the information on the progress made during the three years since the members met last time, but more importantly they record the commitments made by different partners for furthering sweetpotato genetic resources work in Asia. They also contain the recommendations on strategies and approaches proposed at the workshop, which will form the basis for future work of ANSWER. It is my hope that the publication and distribution of this volume will stimulate further the already vigorous activity in sweetpotato genetic resources conservation and use in the region.

The need for broadening a crop’s genetic base may be determined by comparing allele frequencies within the gene pools of farmer selections in their centers of diversity with that of modern breeding populations. The genetic structure of Andean and Chilean potato farmer selections was investigated with the aid of nine isozymes, which have been studied in detail and used to characterize North American cultivars and advanced breeding lines. These isozymes are associated with the most-important agronomic or quality characters in the North American gene pool. By comparing these data with previous analyses of the North American gene pool, allozyme frequency changes for nine loci were monitored. Allozyme frequency changes were not always due to genetic drift, but resulted also from directional selection of isozyme marker linked quantitative trait loci (QTLs) affecting agronomic or quality characters. Changes in allozyme frequency can also occur as a consequence of pleiotropy, i.e. the isozyme itself may be involved in the expression of a phenotype. These allozyme frequency changes may reflect the manipulation of the potato genome by breeders. There were allozymes in some North American cultivars that were not observed in the farmer selections from the Andes and Chile. This confirms that breeders have already introgressed exotic genes from wild and other primitive cultivated tuber-bearing Solanum species. On this basis, the need for broadening the genetic base for specific chromosomes (or chromosome regions) should be based on analysis with these and other genetic markers available in potato.

The need for broadening a crop's genetic base may be determined by comparing allele frequencies within the gene pools of farmer selections in their centers of diversity with that of modern breeding populations. The genetic structure of Andean and Chilean potato farmer selections was investigated with the aid of nine isozymes, which have been studied in detail and used to characterize North American cultivars and advanced breeding lines. These isozymes are associated with the most-important agronomic or quality characters in the North American gene pool. By comparing these data with previous analyses of the North American gene pool, allozyme frequency changes for nine loci were monitored. Allozyme frequency changes were not always due to genetic drift, but resulted also from directional selection of isozyme marker linked quantitative trait loci (QTLs) affecting agronomic or quality characters. Changes in allozyme frequency can also occur as a consequence of pleiotropy, i.e. the isozyme itself may be involved in the expression of a phenotype. These allozyme frequency changes may reflect the manipulation of the potato genome by breeders. There were allozymes in some North American cultivars that were not observed in the farmer selections from the Andes and Chile. This confirms that breeders have already introgressed exotic genes from wild and other primitive cultivated tuber-bearing Solanum species. On this basis, the need for broadening the genetic base for specific chromosomes (or chromosome regions) should be based on analysis with these and other genetic markers available in potato.

Genetic diversity and phenotypic diversity in Verticillium dahliae populations o n cotton were studied among 62 isolates from Spain and 49 isolates from Israel, using vegetative compatibility grouping (VCG), virulence and molecular assays. I n Spain, defoliating V. dahliae isolates (D pathotype) belong to VCG1, and non-d efoliating isolates (ND) belong to VCG2A (often associated with tomato) and VCG4 B (often associated with potato). The D pathotype was not identified in Israel. The ND pathotype in Israel is comprised of VCG2B and VCG4B. Isolates in VCG2B an d VCG4B ranged in virulence from weakly virulent to highly virulent. The highly virulent isolates induced either partial defoliation or no defoliation. Virulenc e characteristics varied with inoculation method and cotton cultivar. Highly vir ulent isolates from Israel were as virulent as D isolates from Spain under condi tions conducive to severe disease. The D pathotype is pathologically and genetic ally homogeneous, whereas the ND pathotype is heterogeneous with respect to viru lence, VCG, and molecular markers based on single-primer RAPD and on PCR primer pairs.

The ability of the late blight pathogen Phytophthora infestans to form oospores in leaves of seven potato cultivars was examined at different incubation temperatures under controlled environmental conditions and under field conditions. At 10°C, the oospore formation in three intermediate‐resistant cultivars all differed significantly from each other (P < 0.05), with the lowest amount formed in cv. Asterix. This latter cultivar did not form oospores at any other temperature. Under field conditions oospores were formed abundantly in a naturally infected field. A significant date by cultivar interaction showed that P. infestans increased the oospore formation in foliage by time in cvs Columbo, Hertha and Matilda, whereas no significant differences between dates were found for other cultivars. The genetic structure of P. infestans in the naturally infected field plot, where oospores formed abundantly, was studied by using amplified fragment length polymorphism and a high genetic diversity was revealed. Oospore germination from two Scandinavian (A1 and A2) P. infestans isolates was stimulated in visible light and in 1 : 2 and 1 : 10 soil extract. The effect of light and nutrients on oosporogenesis is discussed.