An understanding of the genetic relationship within potato germplasm is important to establish a broad genetic base for breeding purposes. The objective of this study was to assess the genetic diversity of potato (Solanum tuberosum subsp. tuberosum Hawkes) germplasm that can be used in the development of cultivars with resistance to late blight caused by Phytophthora infestans (Mont.) de Bary. Thirty-three diploid and 27 tetraploid late blight resistant potato clones were evaluated for their genetic diversity based on 11 isozyme loci and nine microsatellites. A total of 35 allozymes and 42 polymorphic microsatellite fragments was scored for presence or absence. The germplasm was clustered based on the matrix of genetic similarities and the unweighted pair group means analysis of the isozyme and microsatellite data, which were used to construct a dendrogram using NTSYS-pc version 1.7. Twenty-three allozymes and DNA fragments were unique to the wild species. The diploid Solanum species S. berthaultii Hawkes and S. microdontum Bitter formed two distinct phenetic groups. Within S. microdontum, three subgroups were observed. The tetraploid germplasm formed another group, with S. sucrense Hawkes in one subgroup and the cultivated potato and Russian hybrids in another subgroup. Based upon the genetic diversity and the level of late blight resistance, S. microdontum and S. sucrense offer the best choice for strong late blight resistance from genetically diverse sources. This potato germplasm with reported late blight resistance should be introgressed into the potato gene pool to broaden the genetic base to achieve stronger and more durable resistance.

In this study, the use of inter-simple sequence repeats (ISSR) to assess genetic diversity between cultivated potatoes (Solanum tuberosum subsp. tuberosum) is reported. ISSR technology rapidly reveals high polymorphic fingerprints and thus determines the genetic diversity among potato cultivars. Nine primers were selected according to the number of amplified markers and the level of polymorphism detected. Three primers (GAG(CAA)5, CTG(AG)8, and (AG)8) were used to cluster the 28 potato accessions and 77 polymorphic markers were sufficient to identify all of the accessions. Among the 15 simple sequence repeat (SSR) motifs tested, the most abundant were CAA and AG. Argentinian- and European-grown potatoes were easily distinguished, with a higher level of genetic diversity among potatoes from Argentina. An ISSR study using a limited number of cultivars and very few primers clearly differentiated between all cultivars, thus ISSR was revealed to be a good tool for the genetic identification of potato and for future germplasm-management programs.

These proceedings have been compiled and edited jointly by CIP (International Centre for Potato) and IPGRI-APO (International Plant Genetic Resources Institute Regional Office for Asia, the Pacific and Oceania), based on the papers presented at this workshop dealing with objectives as set by ANSWER (Asian Network for Sweetpotato Genetic Resources) members. They contain the information on the progress made during the three years since the members met last time and record the commitments made by different partners for furthering sweetpotato genetic resources work in Asia. They contain critical analysis of feasibility of on-farm conservation of sweetpotato diversity. They also contain the recommendations on strategies and approaches proposed at the workshop which will form the basis for future work of ANSWER. Country Reports on status of sweet potato germplasm collection and maintenance from 11 countries and 8 papers on the concepts, decision tools and strategies of in situ conservation of sweet potato are included

All agricultural crops are severely damaged when not protected against pathogens. A compasison of different means of protection shown that the application of resistance is highly preferable. The great economic importance of this cost-effective and biological safe mean of protection is obvious in all types and areas of plant production. During the last 5 years in Plant genetics and Pathology Department of VASI have done different researches on genetic deversity of pathogens and different plant genetic diversity of materials of rice, groundnut, soybean, potato and taro. A numerous resistance varieties were susscesfully selected and were expanded in large scale in production (such as bacterial will resistance groundnut variety MD. 7, rust resistance and high yield soybean variety DT. 2000). Research on genetic diversity and breeding for resistance by using modern molecular biotechnology methods and also research on sustainable agriculture will give high priority in the next 5 years.

Phytophthora infestans causes a destructive disease on tomato and potato. In North Carolina (NC) potatoes are mostly grown in the east, whereas tomatoes are grown in the mountainous areas in the western part of the state. Five genotypes of P. infestans were identified from 93 and 157 isolates collected from tomato and potato over a 5 year period between 1993 and 1998. All isolates collected from potato in eastern NC were the US-8 genotype, whereas only a single isolate was the US-1 genotype. Tuber blight was found on immature daughter tubers in a single field in 1997, however infection on mature tubers was not observed. Within potato fields, a range of sensitivity to metalaxyl was observed among isolates but all were either intermediate or highly resistant to the fungicide. In contrast, isolates from tomatoes included previously reported US-7 and US-8 genotypes and two new genotypes called US-18 and US-19 (A2 mating type, allozyme genotype Gpi 100/100 and Pep 92/100). These genotypes had unique restriction fragment length polymorphism banding patterns, were sensitive to metalaxyl, and have not been reported elsewhere. All genotypes, with the exception of the US-1, were the Ia mitochondrial haplotype. Thus, isolates of P. infestans from tomato were more genetically diverse over time in NC than those from potato and include two new genotypes that are sensitive to metalaxyl.

Breeding with a diverse population may improve potato (Solanum tuberosum subsp. tuberosum) breeding efficiency for cold chipping cultivars. The objectives of this research were to determine if breeding populations differing in assumed diversity influence the (i) frequency of cold chipping genotypes, (ii) ability to make gain in other traits subsequent to cold chipping selection, and (iii) frequency of genotypes combining high performance across many traits. Three populations or mating groups were constructed with increasing assumed diversity: Tw, Tuberosum within (intrabreeding program crosses); Tb, Tuberosum between (interbreeding program crosses); and Td, Tuberosum diverse (incorporates wild species). Potato chip color was evaluated in Year 1 on up to 20 genotypes per 4x x 4x cross. Genotypes having acceptable chip color were tested in Year 2 for tuber yield (TY), specific gravity (SG), and general tuber appearance (GTA). More Tw genotypes had acceptable chip color (1.7%) than Td (0.6%) or Tb (0.4%) and resulted from a better chip color mean and increased variation. More Td genotypes had acceptable TY (83.3%) in Year 2 than Tw (52.00%) or Tb (42.86%), and may result from increased heterozygosity. Lower numbers of effective breeding individuals in Td reduced genetic variation for all traits and reduced retention for SG and GTA. Retention after 2 yr of selection was significantly higher in Tw (0.7%) due to superior cold chipping, than Tb (0.2%) or Td (0.3%). Diversity can impact breeding efficiency, but mating groups did not predict diversity. Intermating large numbers of unrelated but adapted parents that incorporate favorable cold chipping alleles from wild species may improve breeding efficiency.

The wild potato germplasm of the series Acaulia maintained at the Centre for Genetic Resources, The Netherlands, currently consists of 314 accessions. This collection comprises seed samples of the species Solanum acaule (ssp. acaule, ssp. aemulans, ssp. palmirense and ssp. punae) and Solanum albicans collected from South America. In order to validate taxonomic classification, to investigate the extent of redundancy and to study the distribution of genetic diversity across the collection area, the entire collection was analysed with two AFLP primer pairs on two plants per accession. Within the entire sample a total number of 130 polymorphic bands were scored for the two primer pairs. An UPGMA cluster analysis grouped the majority of plants according to the species and subspecies. A total number of 16 misclassifications were identified, including four cases that did not seem to belong to the series Acaulia. Two accessions were found to consist of plants of different AFLP clusters. AFLP data also allowed the taxonomic classification of the subspecies of 97 accessions that previously were described as S. acaule only. For 126 accessions the two individuals studied displayed identical AFLP profiles. Forty six of these 126 accessions shared their profiles with both or single plants of other accessions. These were all tested for identical profiles for a third primer pair, resulting in 15 duplication groups consisting of a total number of 22 accessions and 14 single plants. Analyses of molecular variance (AMOVA) were performed to examine the distribution of genetic variation. Comparison of geographic distances between the collection site of plants and the number of AFLP polymorphisms revealed no consistent relationship between geographic distance and genetic diversity. AFLP analysis appeared to be an efficient method to verify taxonomic classification and to identify redundancies in the wild germplasm of the series Acaulia. Implications of the results for the ex situ conservation of wild potato germplasm are discussed.

Tropical agricultural systems characterized by swidden-fallow practices have been studied in many tropical areas of the world. One feature of these systems is the high diversity of cultivated species and varieties. The objective of this paper was to analyze the inter and intraspecific diversity of cultivated crops under swidden cultivation systems adopted by caicaras in the Brazilian Atlantic Forest, and the genetic erosion of this diversity in the last decades. To analyze the inter and intraspecific diversity of cultivated crops under swidden cultivation systems in the Brazilian Atlantic Forest, interviews were performed in 33 swidden agriculturists' households concerning the species and varieties under cultivation and others that have been lost. The plots were visited to check the crops cited in the interviews. The agriculturists cited 261 varieties from 53 crop species, with 30.6% of lost varieties. Each agriculturist cited an average of 25 varieties. The main crop was cassava (Manihot esculenta Crantz), followed by yams (Dioscorea spp.), sweet potato (Ipomoea batatas Poir.), squash (Cucurbita pepo L.), sugarcane (Saccharum officinarum L.), and beans (Phaseolus vulgaris L.). Among the interviewed agriculturists, 87% of them have sons and/or daughters not involved in agricultural activity, reflecting a trend toward the loss of the local agricultural skills. A model was proposed to explain the dynamics of the system focusing on the crop diversity and considering the resource resilience. The exchange of crop varieties among agriculturists builds a network which buffers against the loss of the managed diversity in the regional scale. Features such as the itinerancy cycles of fallow/swidden, and the traditional ecological knowledge contribute to the increasing of the managed diversity. However, the agriculturists also pointed out several factors contributing to the depletion of the managed diversity, related to restrictive environmental laws, rural exodus, increasing tourism, and changing of livelihood activities. The loss of crop diversity indicates the urgency for strategies towards the maintenance of the diversity and knowledge tied to the agricultural systems of caicara communities, calling for specific strategies and policies to avoid the loss of their agricultural legacy.

Selection of an appropriate sampling strategy is an important prerequisite to establish core collections of appropriate size to adequately represent the genetic spectrum and maximally capture the genetic diversity in available crop collections. We developed a simulation approach to identify an optimum sampling strategy and core collection size, using isoenzyme data from a CIP germplasm collection on an Andean tetraploid potato. Five sampling strategies, constant (C), proportional (P), logarithmic (L), square-root (S) and random (R), were tested on isoenzyme data from 9396 Andean tetraploid potato accessions characterized for nine isoenzyme loci having a total of 38 alleles. The 9396 accessions, though comprising 2379 morphologically distinct accessions, were found to represent 1910 genetically distinct groups of accessions for the nine isoenzyme loci using a sort-and-duplicate-search algorithm. From each group, one accession was randomly selected to form a genetically refined entire collection (GREC) of size 1910. The GREC was used to test the five sampling strategies. To assess the behaviour of the results in repeated sampling, k=1500 and 5000 independent random samples (without replacement) of admissible sizes n=50(50)1000 for each strategy were drawn from GREC. Allele frequencies (AF) for the 38 alleles and locus heterozygosity (LH) for the nine loci were estimated for each sample. The goodness of fit of samples AF and LH with those from GREC was tested using the ?2 test. A core collection of size n=600, selected using either the P or the R sampling strategy, was found adequately to represent the GREC for both AF and LH. As similar results were obtained at k=1500 and 5000, it seems adequate to draw 1500 independent random samples of different sizes to test the behaviour of different sampling strategies to identify an appropriate sampling approach, as well as to determine an optimum core collection size.

Selection of an appropriate sampling strategy is an important prerequisite to establish core collections of appropriate size in order to adequately represent the genetic spectrum and maximally capture the genetic diversity in available crop collections. We developed a simulation approach to identify an optimal sampling strategy and core-collection size, using isozyme data from a CIP germplasm collection on an Andean tetraploid potato. Five sampling strategies, constant (C), proportional (P), logarithmic (L), square-root (S) and random (R), were tested on isozyme data from 9,396 Andean tetraploid potato accessions characterized for nine isozyme loci having a total of 38 alleles. The 9,396 accessions, though comprising 2,379 morphologically distinct accessions, were found to represent 1,910 genetically distinct groups of accessions for the nine isozyme loci using a sort-and-duplicate-search algorithm. From each group, one accession was randomly selected to form a genetically refined entire collection (GREC) of size 1,910. The GREC was used to test the five sampling strategies. To assess the behavior of the results in repeated sampling, k = 1,500 and 5,000 independent random samples (without replacement) of admissible sizes n = 50(50)1,000 for each strategy were drawn from GREC. Allele frequencies (AF) for the 38 alleles and locus heterozygosity (LH) for the nine loci were estimated for each sample. The goodness of fit of samples AF and LH with those from GREC was tested using the χ 2 test. A core collection of size n = 600, selected using either the P or the R sampling strategy, was found adequately to represent the GREC for both AF and LH. As similar results were obtained at k = 1,500 and 5,000, it seems adequate to draw 1,500 independent random samples of different sizes to test the behavior of different sampling strategies in order to identify an appropriate sampling approach, as well as to determine an optimal core collection size.