Gibberella pulicaris is the sexual stage of Fusarium sambucinum, the major cause of potato tuber dry rot in North America and Europe. In a previous study 42 strains from dry-rotted tubers in North America were analyzed for genetic diversity by mating type and vegetative compatibility group (VCG) tests. In the present study, an additional 96 strains from North America, 21 strains from Europe, and six strains from other geographic areas were analyzed. Both mating types, MAT1-1 and MAT1-2, occur widely outside North America. In contrast, all but two, Canadian, strains of the 138 North American strains analyzed to date are MAT1-1. VCG analysis provides additional evidence that genetic diversity of G. pulicaris from potato tubers is high in Europe but low in the United States. These results suggest that the potential for pathogen change due to sexual recombination is low in the United States, but may be higher in Europe. Limited genetic diversity of G. pulicaris in the United States indicates that there are likely to be few barriers to heterokaryon formation and asexual recombination in the field. Thus, the potential exists for rapid spread and persistence of advantageous mutations throughout the G. pulicaris population, which may have contributed to the recent proliferation of strains resistant to the fungicide thiabendazole which has been widely used to control tuber dry rot.

The use of biotechnologies could allow breeders to overcome some of the difficulties relevant to conventional potato breeding. It provides, in fact, new tools for the study of the genetic control of agronomic characters and for the exploitation of the genetic diversity available both in wild Solanums and other sources. In this paper, we have discussed the use of haploids and meiotic mutants as an efficient and effective method of capturing and transmitting genetic diversity from unadapted germplasm to the cultivated potato. The features and the significance of interspecific and intraspecific somatic hybrids have been taken into account as well. Much attention has also been given to the use of molecular markers for mapping genes of interest and to evaluate genetic distances among genotypes. Finally, the new options provided by genetic transformation in breeding for pest and disease resistance have been discussed | Alcune delle difficolta' che si incontrano nel miglioramento genetico della patata coltivata possono essere superate con l'uso delle moderne biotecnologie. Queste, infatti, facilitano gli studi sul controllo genetico di caratteri di importanza agronomica e permettono una piu' ampia utilizzazione della variabilita' genetica presente nel genere Solanum o anche di sfruttare quella derivante da altre fonti, vegetali e non. Nel presente lavoro e' stata discussa l'importanza e l'utilizzazione degli aploidi e dei mutanti meiotici come strumento per catturare e trasferire nelle varieta' coltivate la variabilita' genetica presente in Solanum e sono state altresi' analizzate le caratteristiche dell'ibridazione somatica intraspecifica ed interspecifica. Si e' discusso l'uso dei marcatori molecolari per mappare geni di interesse e per valutare le distanze genetiche tra particolari genotipi. E' stata infine presa in considerazione la trasformazione genetica, soprattutto in vista di una sua utilizzazione nel miglioramento genetico per migliorare le caratteristiche qualitative e indurre resistenza a malattie e ad insetti

Seventy-seven isolates of the potato and tomato late blight disease pathogen, Phytophthora infestans, from the United States, Canada, and northwestern Mexico, were tested for pathogenicity to nine potato and three tomato cultivars carrying different genes for resistance. Based on previous analyses of mating type, allozyme, and DNA fingerprint data, these isolates had been assigned to eight different clonal lineages. When the total pathogenic variation was partitioned into within- and among-lineage components using the Shannon information statistic, most (63%) of the variation was due to differentiation among lineages; only 37% of the total pathogenic diversity was due to variation within lineages. Older lineages had more pathogenic variation than did those that were more recently introduced into the United States and Canada. Isolates pathogenic to all of the potato differential cultivars were found within two lineages; four isolates infected all of the potato and tomato differentials tested. Variation within lineages is probably the result of rapid evolution after migration, and suggests that mutation rates at pathogenicity loci are higher than those at the molecular loci that defined each genotype. Mutation, selection, and genetic drift have probably all contributed to the pathogenic variation observed within clonal lineages of P. infestans in the United States and Canada.

Genetic diversity among isolates of the bacterial plant pathogen Burkholderia solanacearum (synonym Pseudomonas solanacearum) race 3 biovar II of Kenya was determined by PCR with repetitive sequences (ERIC and BOX repetitive primer sets) and pulsed-field gel electrophoresis of genomic DNA digested by rare-cutting restriction endonucleases (RC-PFGE). The study comprised 46 isolates collected during 1992 from the major potato-growing regions of Kenya (45 were identified as race 3 biovar II, and 1 belonged to race 3 biovar N2) and 39 reference isolates from 19 other countries. RC-PFGE identified 10 distinct profile types among the Kenyan race 3 biovar II isolates (29 of the isolates exhibited identical profiles) and a further 27 distinct profile types among the reference isolates. ERIC and BOX primer sets were unable to differentiate race 3 biovar II isolates within the Kenyan population but differentiated a further two distinct profile types among the reference isolates. The race 3 biovar N2 isolate had a highly distinct RC-PFGE and repetitive sequence PCR profile. Statistical analysis of the data identified biogeographic trends consistent with conclusions drawn from previous studies on the origin and worldwide dissemination of race 3 biovar II isolates; however, genomic fingerprinting by RC-PFGE revealed a level of genetic diversity previously unrealized.

The diploid cultivated and wild species, which represent 70 percent of all tuber-bearing species of Solanum, are the supply of germplasm and a source of genetic diversity and genes of resistance and starch, protein and dry matter content. They are crossed very easily with dihaploid forms of Solanum tuberosum. Both are used in potato research and breeding programmes. Dihaploid clones and diploid species of our collection aare planted in the field in the form of 15, 10 qnd 5 tubers according to virus resistance, tuber characteristics, fertility and unreduced gametes production. The best clones are maintained in vitro. About 600 clones are maintained in field collections, 80 clones in vitro, and Solanum phureja, S. maglia, S. brevidens, S. bulbocastanum, S. vernei, S. chacoense, S. gourtei and S. berthaultii

The Asian Vegetable Research and Development Center (AVRDC), created in 1971 and based in Taiwan, was originally the brainchild of the United States Agency for International Development (USAID). From the beginning, the fundamental goal of AVRDC has been to increase the production and quality of vegetables through improved varieties, increased disease and pest resistance/tolerance, increased heat tolerance and better cultural practices. Research concentrated initially on six vegetables: tomato, soy bean, mungbean, sweet potato, white potato and Chinese cabbage. Sweet potato and white potato were later dropped from the research programme and replaced over a period of time by three other major crops: pepper, alliums (onion, shallot, garlic) and eggplant. Genetic resources AVRDC collects and stores as many cultivars of its mandated crops as possible. Its Genetic Resources and Seed Unit (GRSU), constructed in 1984, is a large cold-storage facility capable of keeping some varieties of seed viable for as long as a century. By September 1995, GRSU had a total of 37,938 accessions of its principal crops and 5,404 accessions of non-prinicipal but regionally important crops. The unit holds the world's base collection of mungbean and pepper. The material provides a broad genetic base for vegetable breeding and safety backups against the risk of a limited and highly uniform gene pool. Requests for seed samples of material in the collections as well as information about breeding lines are regularly received. Ongoing research aims to establish sets of core collections and to generate information that will lead to better management of vegetable genetic resources. This includes the use of statistical, cytological, biochemical, and molecular tools in the analysis of genetic diversity and genetic changes at different phases of germplasm maintenance. The germplasm is made available to researchers. One of AVRDC's major achievements is the development of tomato varieties that yield well under hot, humid conditions. A rich source of vitamin C, tomato is a popular cash crop for small farmers and home gardeners throughout much of the world. The principal problems with tomato in the hot, humid tropics are poor fruit set and disease. The challenge for AVRDC's tomato breeders was to combine heat tolerance and disease resistance with desirable culture and eating characteristics. Today the GRSU's active collection of cultivated tomato and wild relatives is one of the largest in the world. Application of biotechnology Molecular techniques are used to understand the biology of the principal vegetables at the molecular level, in order to genetically engineer varieties that might otherwise take years to complete using conventional plant breeding methods. Biotechnology has assisted AVRDC plant breeders to produce mungbean varieties which are highly resistant to bruchids, a major pest of stored beans throughout the world. Current activities include tissue culture and transformation, pest and stress control, quality improvement and genetic mapping. Biotechnological research is one of the primary areas in which AVRDC collaborates with universities worldwide. Spreading the word To bring AVRDC closer to its partners and respond more effectively to differences in needs and capabilities among regions, the Center has established regional networks in Southeast Asia, South Asia and Southern Africa. In 1992 AVRDC signed an agreement with the Southern African Centre for Cooperation in Agricultural Research (SACCAR). to be the executing agency for the Collaborative Network for Vegetable Research and Development in Southern Africa (CONVERDS). There are ten participating countries in the region: Angola, Botswana, Lesotho, Malawi, Mozambique, Namibia, Swaziland, Tanzania, Zambia and Zimbabwe. The network is based at Horti, Tengeru near Arusha, Tanzama. Through its International Cooperation Programme, AVRDC assists in strengthening and enhancing national vegetable research and development capacity through information and communication services, collaborative research, technology transfer and institution building. AVRDC has recognized the very important role it can play in the development of human resources for vegetable research and extension, both through its training programmes and through the development of training materials. The Center's aim is to create a critical mass of well-trained and motivated researchers within the national agricultural programmes of developing countries themselves. Good information exchange is also vital to the development of national capacity. The Center operates a Selective Dissemination of Information (SDI) service for national programmes. It produces and publishes commodity-specific quarterly updates which, abstracted from the latest worldwide horticultural information sources on these commodities, are available at no charge from AVRDC. Copies of selected articles from the SDI listings can be obtained on request. In addition a Tropical Vegetable Information Service (TVIS) project has established a computer retrieval system using the software MINISIS. The AVRDC library is a major repository of information on vegetable improvement and the Center is a leading publisher and distributor of vegetable research information. Publications from the Office of Publications and Communications (OPC) are distributed to more than 600 libraries and to individuals in 160 countries. The Center's bi-annual newsletter Centerpoint contains up-to-date news on the Center's courses, conferences, research and projects. AVRDC PO Box 42 Shanhua Tainan TAIWAN Tel: +886 6 583 7801 Fax +88665830009 E-mail avrdc@cgnet.com avrdcyt@mail.ncku.edu.tw avrdc@C6hinet.net | The Asian Vegetable Research and Development Center (AVRDC), created in 1971 and based in Taiwan, was originally the brainchild of the United States Agency for International Development (USAID). From the beginning, the fundamental goal of AVRDC has...