Stem necrosis caused by a Groundnut bud necrosis virus is a serious disease of potato in central India. In order to find sources of resistance to this disease, 207 exotic accessions of cultivated potato were screened under natural conditions in fields at Gwalior for three successive years. A large number of accessions(33.8%) were found to be resistant to highly resistant. These can be used in potato breeding programme for developing varieties adopted to the region and having resistance to stem necrosis.

Potato (Solanum tuberosum L.) cultivated in North America is an autotetraploid species with a narrow genetic base. Most of the popular commercial cultivars are susceptible to Verticillium dahliae, a fungal pathogen causing Verticillium wilt disease, though some cultivars with relatively high resistance also exist. We have used the available pedigree information to track the origin of susceptibility and resistance to Verticillium wilt present in cultivated potatoes. One hundred thirty-nine potato cultivars and breeding selections were analyzed for resistance to the pathogen and for the presence of the microsatellite marker allele STM1051-193 that is closely linked to the resistance quantitative trait locus located on the short arm of chromosome 9. We detected an unusually high frequency of susceptible genotypes in the progeny descending from the breeding selection USDA X96-56. Molecular analysis revealed that USDA X96-56 does not have the STM1051-193 allele. Most of the first-generation progeny of this breeding selection also lack the allele. On the other hand, pedigree analysis indicated that breeding selection USDA 41956 often transfers V. dahliae resistance to its progeny. Molecular analysis detected presence of (at least) three STM1051-193 alleles in this breeding selection. These two genotypes (USDA X96-56 and USDA 41956) appear to have contributed greatly to the susceptibility or resistance, respectively, found in present commercial cultivars. Our results also indicate that the maturity class substantially affects the plant resistance response. In the intermediate to very late maturing class, the presence of the STM1051-193 allele significantly increases the resistance. Early to very early potatoes are usually more susceptible to the disease regardless of the allelic status, though the pattern of the allele effect is always the same. The results indicate that the STM1051-193 allele can be used for marker-assisted selection, but the potato maturity class also needs to be considered when making the final decision about the plant resistance level.

Tuber soft rot and early blight are serious potato diseases. Development of potato varieties resistant to these diseases has been hindered by the scarcity of resistant germplasm. A diploid wild species, Solanum brevidens, shows significant resistance to both diseases. Numerous potato breeding lines have been developed from a potato-S. brevidens somatic hybrid, A206. A BC3 clone, C75-5+297, derived from this somatic hybrid as well as its BC1 and BC2 parental lines showed resistance to both tuber soft rot and early blight. Clone C75-5+297 has consistently out-yielded common varieties under disease stress. Using both molecular and cytogenetic approaches we demonstrated that a single copy of chromosome 8 from S. brevidens replaced a potato chromosome 8 in C75-5+297. Thus, C75-5+297 represents a potato-S. brevidens chromosome substitution line. Our results suggest that the presence of a single chromosome from S. brevidens may significantly impact the resistance to multiple potato diseases. The high yield potential of C75-5+297 makes it an excellent parent for developing potato varieties with resistances to both tuber soft rot and early blight.

Bacterial wilt of vegetable crops caused by Ralstonia solanacearum is very damaging in tropical and subtropical humid countries. In Jirof and kahnouj regions, this pathogen is one of the most limiting factors for potato production. As for other vascular bacterial plant diseases, chemicals are not effective and sanitation measures are difficult to apply. The worldwide control strategy consist of breeding wilt- resistance cultivars. During 2001- 2002, Farmers field of potato in Jiroft were surveyved for bacterial wilt percentage in autumn and winter cultivations. In addition in microplat and greenhouse experiments, 19 commerical potato cultivars were evaluated for resistance to R. solanacearum (race 3/ biovar 2-A). plants were inoculated on the basis of winstead and kelman’s root and stem inoculation method with GD1 strain, isolated from wilted potato in Jiroft. Disease reaction of cultivars were rated on the basis of disease severity index(DSI) and the “MSTATC” soft ware package was used for data analaysis. The results indicated that singnificant differences in DSI were observed among the root inoculated potato cultivars. N0 cultivars were immune or resistant, but Santana, Aula and Marfona showed more tolerance. Diamont and Primir were the most susceptible cultivars in this study.

A comparative study of different parameters calculated for foliage resistance of potato to Phytophthora, infestllns (Mont.) de Bary was conducted on the data for 27 cultivars and Qne prebreeding clone in field assessment in 2003 at BAZ GroB L'Osewitz. Relationships between the parameters and maturity were detennined by linear regression. The strongest associations with maturity were found for the relative area under the disease progress curve (RAUDPC), delay of attack, and attack on a determined date (r² = 0.4 7-0.52). The least association with maturity was found for foliage blight resistance at GroB Li.isewitz, FBRGL (r² = 0.03), calculated by using a maturity-dependent section of the disease progress curve. The apparent infection rate (AIR), RAUDPC and delay of attack could only explain below 50% of variability of FBRGL,. The method for calculation of foliage resistance in breeding developed at BAZ and named FBRoL is described in detail, and the usefulness of the different methods for evaluation of resistance, management of plant protection and breeding is discussed.

Verticillium wilt is a serious disease in potato and is caused primarily by the soilborne fungi Verticillium dahliae and V. albo-atrum. Host plant resistance to the disease offers an option for long-term, inexpensive, and environmentally sound control. High levels of resistance to stem colonization have been identified in two diploid hybrids between the cultivated potato and wild Solanum spp. An intercross between the two clones produced a 3:1 ratio of resistant to susceptible clones. A cross between a susceptible clone and one of the resistant clones also produced a 3:1 resistant:susceptible ratio. These data can be explained by a two-gene model, in which dominant alleles of both genes must be present to confer resistance. The two-gene model also explains data from previous research with wild Solanum spp. A simple mode of inheritance should improve the probability of producing resistant offspring when resistant hybrids are used as parents in a breeding program.

Late blight, caused by Phytophthora infestans (Mont.) de Bary, is the most destructive disease of potato worldwide. As this pathogen can rapidly overcome major race-specific resistance genes, identifying the basis for enhanced quantitative resistance has become a crucial element for implementing advanced breeding strategies. A population of 230 full-sib progeny derived from a cross between two diploid hybrid Solanum phureja x S. stenotomum clones was evaluated for foliage resistance against late blight in replicated trials at multiple locations in Pennsylvania between 1999 and 2002. In field experiments, plants were evaluated visually for per cent defoliation, and area under the disease progress curve (AUDPC) was determined. The two parents and three control cultivars ('Atlantic', 'Kennebec' and 'Katahdin') were included in all trials. In all three experiments, the presence of a significant number of clones exhibiting transgressive segregation were observed. There were significant differences among environments as well as among clones, and the clone x environment interaction was also significant. Stability analysis revealed that 37 clones made a significant contribution to the overall environment x clone interaction. Broad-sense heritability for resistance, measured as AUDPC, was estimated as 0.67. The overall results indicate the presence in this potato family of a high level of field resistance against late blight. This segregating diploid family appears to be a good candidate for quantitative trait loci mapping to identify and characterize the genetic components of partial late blight resistance.

Powdery scab of potato, once established in a field, is difficult to control because of the longevity of the resting spores (cystosori) of the causal organism, Spongospora subterranea f.sp. subterranea. Host resistance is likely to be the most efficient in a long-term control strategy for preventing build-up of field inoculum and spread of the disease. Resistance screening of potato cultivars is mostly done in laborious field trials where disease development is likely to be unpredictable. A bioassay with potato tissue cultured plantlets and cystosori as inoculum is described and was tested for its potential to screen potato cultivars at an early stage for their relative susceptibility to powdery scab by comparing the lab results with field data. With cystosori inoculum of Swiss origin, the laboratory test showed clear differences between the potato cultivars in the severity of zoosporangial root infection which correlated better with ranked tuber infection data, compared to root galling. There are apparent differences in the relative trends in susceptibility between roots and tubers of five selected cultivars when using naturally infested soil instead of prepared cystosori as inoculum in the lab bioassay. Furthermore, differences in the severity of zoosporangial root infection of two selected cultivars were found when cystosori from different countries where used as inoculum. A possible host genotype x pathogen interaction is discussed. The bioassay has the potential to screen and select for resistant material at an early breeding stage thus making field trials not unnecessary but more economical. It will allow the use of a standard set of pathogen collections and facilitate testing for inoculum virulence in infested soils.

For evaluating the resistance of Black sigatoka in genotypes from breeding programmes different methods have been used, the artificial inoculation of pathogens reproduction structures is one of them. Nevertheless, is necessary the standardization of condition for it in vitro production and to know the response of cultivars to the diseases in greenhouse. It will permit to establish methods for evaluating and selecting the new resistant genotypes. This work was carried out with the objectives to evaluate different culture media and incubation conditions for obtaining P. fijiensis conidia and for evaluating the response of two cultivars to the artificial inoculation with conidial suspensions of this fungus. Different culture media and incubation conditions for obtaining the conidia and the cultivars Grande naine (susceptible) and FHIA-18 (partially resistant) were used. The conidia of P. fijiensis could be obtained in vitro at 20ºC and constant light from 10 days of incubation in culture media Potato Carrot Agar, modified V-8 Agar and Potato Dextrose Agar. However, the greatest concentration was reached in Potato Dextrose Agar after 20 days of incubation at 20ºC under continuous white fluorescent light. The artificial inoculation of conidial suspensions of P. fijiensis allowed to evaluate the response of Grande Naine and FHIA-18 cultivars in greenhouse. By the use of qualitative scale of symptoms stages and the quantitative variables symptoms evolution time and disease development time was possible to differentiate both cultivars. They maintained in greenhouse similar response to the disease that in the field. Key words: conidia, culture medium, FHIA-18, Grande naine, sporulation

Die Entwicklung von Transformations- und Klonierungstechniken eröffnet neue Wege in der Züchtung von Kulturpflanzen. Durch diese Verfahren wird es möglich, Gene aus verschiedenen Organismen in Pflanzen zu exprimieren. Ziel der molekularen Pflanzenzüchtung ist die Verbesserung von Qualitätsfaktoren der Kultursorten und die Erhöhung der Krankheitsresistenz insbesondere gegen phytopathogene Pilze. Durch die Übertragung von Fremdgenen, die für Abwehrproteine codieren, kann die Basisresistenz von Pflanzen verändert werden. In dieser Arbeit wurden transgene Kartoffel- und Tabakpflanzen, die die Abwehrproteine Glukanase, Chitinase, RIP oder Kombinationen dieser Proteine exprimierten, mit Hilfe eines Blattscheibentests auf ihre Anfälligkeit gegen wichtige phytopathogene Pilze untersucht. <br /> Die Expression von Glukanase und Chitinase in Tabak führte zu einem signifikant verringerten Befall mit den Pathogenen<em> Botrytis cinerea </em>und<em> Phytophthora nicotianae</em>. Durch die Kombination dieser beiden Abwehrproteine konnte im Vergleich zu Einzelkonstrukten nur eine geringfügig erweiterte Erhöhung der quantitativen Resistenz festgestellt werden. Auch die Kombinationen Glukanase/Chitinase, Glukanase/RIP und RIP/Chitinase in Kartoffelpflanzen der Sorte Désirée führte zu einer deutlich verringerten Anfälligkeit gegen <em>Phytophthora infestans</em>, aber nicht zu einer Erhöhung der Resistenz, die über die Wirkung eines einzelnen Resistenzproteins hinausging. <br /> Für das T4-Lysozym war bislang nur eine bakterizide Wirkung bekannt. Anhand von <em>in vitro</em>-Untersuchungen konnte eine hemmende Wirkung auf keimende Sporen phytopathogener Pilze festgestellt werden. Auch enzymatisch inaktives Lysozym und die Peptide A4 und A23 des T4-Lysozyms wiesen die gleiche Wirkung auf keimende Pilzsporen auf. Dieser Effekt kann wahrscheinlich auf die Wirkung amphipathischer Helices auf Zellmembranen zurückgeführt werden. Mit Hilfe eines Fluoreszenztests konnte die membranschädigende Wirkung des T4-Lysozyms auf Pilzsporen nachgewiesen werden. <br /> Die Expression des T4-Lysozyms in der Kartoffelsorte Désirée unter Kontrolle des konstitutiven 35S-Promotors führte zu einer signifikanten Befallsverringerung nach Inokulation mit <em>Phytophthora infestans</em>. Bei Expression des Proteins unter der Kontrolle des induzierbaren Mannopinsynthase-Promotors konnte jedoch kein signifikanter Effekt festgestellt werden. Transgene T4-Lysozym exprimierende Linien der Kartoffelsorten Panda und Secura, die eine hohe bzw. niedrige natürliche Resistenz gegen <em>P. infestans</em> besitzen, zeigten ebenfalls deutlich verringerten Befall mit diesem Erreger. | <strong>Effect of several resistance proteins on phytopathogenic fungi in vitro and the resistance effect of these proteins in transgenic potato and tobacco plants</strong><br /> The development of plant transformation and cloning techniques has opened new possibilities in plant breeding research. With these new techniques now it is possible to transfer genes from different organisms into plants. The objectives of molecular plant breeding are to optimise crop quality and to increase the disease resistance of plants to phytopathogenic fungi. Especially, the basic resistance of plants can be improved by the transfer of foreign genes coding for pathogenesis related proteins. In this paper transgenic potato and tobacco plants expressing the PR-proteins glucanase, chitinase, RIP, or a combination of two of these proteins, respectively, were studied for their resistance to several fungal plant diseases using a leaf disc assay. <br /> Tobacco lines expressing glucanase or chitinase, resp., showed significantly reduced infection with the pathogens Botrytis cinerea and <em>Phytophthora nicotianae</em>. In comparison to these lines, the combination of the two PR-proteins led only to a slight further enhancement of resistance of tobacco plants. Furthermore, the co-expression of glucanase/chitinase, glucanase/RIP or RIP/chitinase, resp., in the potato variety Désirée resulted in significantly reduced disease symptoms after infection with<em> Phytophthora infestans</em> but not to a resistance increase higher than the resistance of lines expressing only one foreign protein. <br /> The lysozyme of the T4 bacteriophage is known to be bactericidal. Using <em>in vitro</em> assays, an inhibitory effect on germinating spores of phytopathogenic fungi was detected in this work. The same effect was shown for enzymatic inactive T4-lysozyme and for the synthesised peptides A4 and A23 of the C-terminus of T4-lysozyme. Thus, the fungistatic effect is likely ascribed to the membrane disturbing activity of amphipathic helices these peptides are coding for. Using a fluorescence test the membrane disturbing activity of T4-lysozyme on fungal spores could be proven.<br /> The expression of T4-lysozyme in potato plants (var. Désirée) under control of the 35S-promoter confers significantly increased resistance to <em>Phytophthora infestans</em>. Whereas potato plants expressing the T4-lysozyme gene under control of the mannopine-synthase promoter showed no significant <em>Phytophthora resistance</em>. Further resistance tests indicate that transgenic T4-lysozyme expressing potato lines of the varieties Panda and Secura, which have high or low natural resistance to <em>Phytophthora leaf </em>blight, resp., show significant enhanced resistance, too.