Potato is one of our most important crop because of its rule supplying with food. Out of the cultivated plants potato has the most pathogens. Potato Y potyvirus (PVY) is the type member of potyvirus genus of Potyviridae family, which constitutes the largest known and economically most important family of plant viruses. A new strain of PVY, which produces severe necrotic ring symptoms on potato tubers was isolated at the first time by Beczner et al. (1982) in Hungary. This strain belongs to the tobacco veinal necrosis strain group. The new strain was named by Horv th (1992) which was accepted by the Virology Section of EAPR (European Association for Potato Research). The acronym of this new strain is: PVY(N(ew) T(uber) N(ecrosis))=PVYNTN. The potato tuber necrotic ringspot disease (PTNRD) is identified by superficial bows and rings around the eyes, first protruding, later becoming sunken and necrotic. Furthermore PVYNTN is suspected to overcome field resistance of numerous potato cultivars therefore, this is a resistance breaking strain of PVY. This virus strain became distributed throughout Europe and other parts of the word. The identification of resistance sources is of great importance, therefore experiments were carried out with wild Solanum species for determining their susceptibility or resistance to NTN strain of PVY. The objective of the study was to identify potential resistance sources among the wild Solanum species that could be used in the potato breeding program. We have studied more than 100 wild Solanum species and accessions to PVYNTN. It was found some resistance species and accessions. Currently potato cultivars, resistant to PVY are derived from S. stoloniferum (e.g. 'Szignal'). Out of the resistance species some accessions of Solanum stoloniferum and S. tarnii could be used in the potato breeding. They were immune to the PVYNTN infection.

Early blight disease, caused by Alternaria solani Sorauer, is a serious disease of potato foliage and tubers that occurs in most potato-growing regions world-wide. Developing new potato cultivars with resistance to early blight may reduce losses in the field and in storage, and lessen the need for fungicide applications. A total of 280 clones, derived from 72 maternal half-sib families from a diploid randommated hybrid population of Solanum phureja x Solanum stenotomum were examined for resistance to early blight. The clones that were evaluated in a replicated field trial for 2 years in Pennsylvania, USA, had similar early blight intensity both years. Significant differences were found among families, within families and for the interaction of years x within families. Broad-sense heritability for resistance, measured as area under the disease progress curve (AUDPC), was estimated as 0.73, with a 95% confidence interval of 0.65-0.78, and narrow-sense heritability was estimated as 0.61 +/- 0.29 (P = 0.05). The correlation of AUDPC for early blight between years was 0.57 (P < 0.0001). These results suggest that this diploid population is worthy of use in breeding for early blight resistance.

At least ten years needed to abtain new potato cultivar through sexual hybridization, somatic hybridization or through genetic transformation,T o short cut this process,L aboratory of Biotechnology,D epartmento f Agronomy,I PB employeda strategys o called single seedi n vitro clonal decent( SSICD)b y Usings electedp arental linesf or TPS( True Potato Seed) production. This breeding consist of in vitro pre evaluation for resistance wilt, fusarium wilt, black leg, rot knot nematode and maturity. Using the same number of bacterial cel/ (lif cel/lml), there were positive correlation between in vitro test for disease resistance through dripping test or dripping test with greenhouse test through direct inoculation of Ralstonia solanancearum. Resistant clones to fusarium wilt and verticil/ium were also resistant to bacterial wilt. In vitro tuberization could be use to evaluate maturity of potato cultivar.

At least ten years needed to abtain new potato cultivar through sexual hybridization, somatic hybridization or through genetic transformation,T o short cut this process,L aboratory of Biotechnology,D epartmento f Agronomy,I PB employeda strategys o called single seedi n vitro clonal decent( SSICD)b y Usings electedp arental linesf or TPS( True Potato Seed) production. This breeding consist of in vitro pre evaluation for resistance wilt, fusarium wilt, black leg, rot knot nematode and maturity. Using the same number of bacterial cel/ (lif cel/lml), there were positive correlation between in vitro test for disease resistance through dripping test or dripping test with greenhouse test through direct inoculation of Ralstonia solanancearum. Resistant clones to fusarium wilt and verticil/ium were also resistant to bacterial wilt. In vitro tuberization could be use to evaluate maturity of potato cultivar.

Hevea leaf fall disease caused by Corynespora cassiicola (Berk & Curt) Wei, is one of the major disease constraints to the production of natural rubber (Hevea brasiliensis) in South Cameroon. Attempts to control this disease by traditionally recommended practices such as artificial defoliation or aerial spray of fungicides have not yielded satisfactory results in Cameroon. Production of disease resistant planting material may provide a more efficient disease control strategy. As part of a screening process of a large pool of Hevea genetic resources for disease resistance, we evaluated in-vitro. 28 genotypes collected from Amazonia. These genotypes were tested for resistance to two isolates of C. cassiicola (NK01 and NK02), obtained from different clones showing different levels of susceptibility to the disease in the same field in South Cameroon. The two isolates had similar growth characteristics on culture media. However, isolate NK01 grew faster than NK02 on Potato Dextrose Agar and was also more virulent on the lest material. The two isolates may belong to different races. To verify this, further characterisation of the isolates is recommended. Significant differences were observed in the response of the tested Hevea genotypes to each of the isolates. Genotypes AC/S/12/22, RO/07/48. and AC/B/19/22 had the highest resistance to both isolates. These could constitute good source material in breeding for disease resistance. Due to their high susceptibility to both isolates, genotypes AC/S/12/02, MT/I/25, MT/C/04/22, MT/C/04/27 and RO/C/08/33 may have to be avoided in any such breeding programme.

Açúcares redutores e matéria seca são características muito importantes em batata para processamento. Duas espécies de batata silvestre, Solanum commersonii, subespécies commersonii e malmeanum, e S. chacoense, subespécie muelleri, ocorrem no Sul do Brasil. Essas espécies são importantes para programas de melhoramento, pois apresentam variabilidade para diversas características importantes, tais como, tolerância à seca e geada, resistências a doenças e insetos e teor de matéria seca. Os objetivos deste trabalho foram verificar a variabilidade genética e estimar a herdabilidade para teor de açúcares redutores em clones de batata silvestre, que ocorrem no Sul do Brasil. Cinqüenta clones de batata silvestre, tomados ao acaso, da coleção mantida na EMBRAPA - Clima Temperado foram cultivados, sob telado, no outono e na primavera de 1996. No outono, 30 e, na primavera, 40 clones produziram tubérculos para análise de açúcares redutores. Os teores de açúcares redutores dos tubérculos foram determinados pelo método de Lane Enyon e identificados pelo método de Somogyi, modificado por NELSON (1944). Os resultados indicaram que as espécies estudadas apresentam variabilidade para teor de açúcares redutores, com alta herdabilidade, principalmente no outono.<br>Reducing sugar and dry matter are very important traits in potatoes for processing. Two wild potato species, Solanum commersonii, subspecies commersonii and malmeanum, and S. chacoense, subspecie mu, occur in the South of Brazil. These species are important for breeding programs, since they have variability for several important traits, such as drought and frost resistance, disease and insect resistance, and dry matter content.. The objectives of this research were to verify the genetic variability for reducing sugar content in wild potato clones of species that occur in this region and to estimate its heritability. Fifty wild potato clones, aleatorily chosen, of Embrapa Clima Temperado collection were grown in screen house, in autumn and spring season of 1996. In autumn, 30 and, in spring, 40 clones produced tubers for the reducing sugar analysis. Tuber sugar content was determined by using the Lane Enyon method and identified by the Somogyi method, modified by NELSON (1944). The results indicated that these species have genetic variability for reducing sugars, with high heritability, mainly in the fall season.

Reducing sugar and dry matter are very important traits in potatoes for processing. Two wild potato species, Solanum commersonii, subspecies commersonii and malmeanum, and S. chacoense, subspecie mu, occur in the South of Brazil. These species are important for breeding programs, since they have variability for several important traits, such as drought and frost resistance, disease and insect resistance, and dry matter content.. The objectives of this research were to verify the genetic variability for reducing sugar content in wild potato clones of species that occur in this region and to estimate its heritability. Fifty wild potato clones, aleatorily chosen, of Embrapa Clima Temperado collection were grown in screen house, in autumn and spring season of 1996. In autumn, 30 and, in spring, 40 clones produced tubers for the reducing sugar analysis. Tuber sugar content was determined by using the Lane Enyon method and identified by the Somogyi method, modified by NELSON (1944). The results indicated that these species have genetic variability for reducing sugars, with high heritability, mainly in the fall season. | Açúcares redutores e matéria seca são características muito importantes em batata para processamento. Duas espécies de batata silvestre, Solanum commersonii, subespécies commersonii e malmeanum, e S. chacoense, subespécie muelleri, ocorrem no Sul do Brasil. Essas espécies são importantes para programas de melhoramento, pois apresentam variabilidade para diversas características importantes, tais como, tolerância à seca e geada, resistências a doenças e insetos e teor de matéria seca. Os objetivos deste trabalho foram verificar a variabilidade genética e estimar a herdabilidade para teor de açúcares redutores em clones de batata silvestre, que ocorrem no Sul do Brasil. Cinqüenta clones de batata silvestre, tomados ao acaso, da coleção mantida na EMBRAPA - Clima Temperado foram cultivados, sob telado, no outono e na primavera de 1996. No outono, 30 e, na primavera, 40 clones produziram tubérculos para análise de açúcares redutores. Os teores de açúcares redutores dos tubérculos foram determinados pelo método de Lane Enyon e identificados pelo método de Somogyi, modificado por NELSON (1944). Os resultados indicaram que as espécies estudadas apresentam variabilidade para teor de açúcares redutores, com alta herdabilidade, principalmente no outono.

Ever since the late blight epidemics of the mid-nineteenth century, man has endeavored to protect his potato crop. Every year, extensive chemical protection is applied, which is expensive and may be harmful to the natural environment. The use of resistant potato cultivars would provide an elegant alternative, however breeding for late blight resistance has not yet resulted in adequately resistant cultivars. In addition to the demand for a high level of resistance, the resistance should be durable. The causal agent of the late blight disease is Phytophthora infestans , a biotrophic oomycete pathogen. Oomycetes are often incorrectly referred to as fungi, but they evolved the ability to infect plants independently from fungi, and may therefore have distinct mechanisms for interacting with plants. Insight in the mechanisms of resistance to P.&nbsp;infestans may assist the breeders in their operation to achieve durable resistance.Genetic resistance can be determined at the subspecies or variety level (race-specific resistance), or at the species or genus level (nonhost resistance). Nonhost resistance is full resistance, and is present in most plant species. In addition, resistance may be a quantitative trait (partial resistance). A rich pool of diverse resistances to P.&nbsp;infestans has been found in wild Solanum species, with levels ranging from full resistance to various levels of partial resistance. Some old potato cultivars also exhibit partial resistance, which proved to be durable. To achieve a durable late blight resistance, a better understanding of the molecular basis of the various types of resistances is essential. To this end, we compiled a set of Solanum species with various types and levels of resistance to P.&nbsp;infestans , and studied the cellular and molecular aspects of the resistance mechanisms present in these plants.Laboratory studies at the cellular and molecular level require an experimental assay, which is both comparable to the natural situation, and assures a high percentage of successful infections. To this end, we developed a resistance assay with detached leaves under controlled conditions in the laboratory and compared this assay with a field trial. The tested growing conditions of the plants did not affect the resistance to P.&nbsp;infestans. Leaves on intact plants however, were more resistant than detached leaves. The incubation conditions of the detached leaves in the laboratory assay rather than the detachment itself appeared to affect the resistance expression. However, on intact plants the infection frequency was too low for molecular studies. Since the ranking of resistance levels within a set of twenty plant clones was similar under laboratory and field conditions, the laboratory assay proved adequate to study the Solanum - P.&nbsp;infestans interaction.A cytological survey of the interaction between twenty Solanum clones and three P.&nbsp;infestans isolates provided the first impression of the nature of the resistance responses. Potato cultivars with race-specific resistance ( R ) genes displayed the hypersensitive response (HR), a programmed cell death of plant cells, upon inoculation with P.&nbsp;infestans . Through this rapid cell death, the biotrophic pathogen became localized between dead cells, and was prevented from further growth. Also durably resistant potato cultivars without known R genes, wild Solanum species, and nonhosts displayed the HR. Interestingly, in highly resistant Solanum species such as S. berthaultii and S&nbsp;circaeifolium, and nonhosts such as Arabidopsis thaliana and S.&nbsp;nigrum (black nightshade), the HR was extremely fast and effective, resulting in very localized cell death. In partially resistant plants, the HR was delayed, and resulted in larger HR lesions. Occasionally, hyphae were able to escape from these lesions and established a biotrophic interaction with the host. The effectiveness of the HR in restricting growth of the pathogen differed considerably between clones, and correlated with resistance levels. In addition to the HR, local depositions of callose and phenolic compounds occurred, which may function as physical barriers. Although these responses did not correlate with resistance levels, they may influence the balance between growth of the pathogen and induction of the HR. Ultimately, this fine balance may determine resistance at the cellular level, and illustrates the quantitative nature of the resistance to P.&nbsp;infestans at the plant or field level .The HR is initiated upon recognition of pathogen elicitors by plant cell receptors or R gene products as suggested by the gene-for-gene hypothesis. Several types of R genes are recognized in plants, including the nucleotide binding site leucine-rich repeat (NBS-LRR) type, and the Pto-like serine/threonine protein kinase type. The Pto gene was originally identified from wild relatives of tomato. We exploited our Solanum collection to identify Pto -like sequences, and studied evolutionary scenarios for Pto -like genes. Polymerase chain reaction (PCR) amplifications using primers based on conserved and variable regions of Pto yielded 32 intact Pto -like sequences from six Solanum species, and revealed an extensive Pto family. Pto -like transcripts were also detected in leaf tissue of all tested plants. The kinase consensus and autophosphorylation residues were highly conserved, in contrast to the kinase activation domain which is involved in ligand recognition in Pto. Phylogenetic analyses distinguished nine classes of Pto -like genes, and revealed that orthologues (homologues separated by a speciation process) were more similar than paralogues (homologues generated by a gene duplication event). This suggests that the Pto gene family evolved through a series of ancient gene duplication events prior to speciation in Solanum . The phylogenetic data are in line with recent results on the NBS-LRR class of R genes, and suggest that Pto- like genes are ancient, and highly diverse.Various levels of nonspecific resistance were revealed in Solanum species after inoculation with five P.&nbsp;infestans isolates. In partially resistant plants where hyphal escape occurred, the lesions expanded often slower than in susceptible plants. Here, defense mechanisms other than HR are thought to operate; this might for example involve systemic acquired resistance (SAR). SAR can be induced by various signals, but also basal levels of SAR may vary between plants. When we monitored basal expression levels of SAR marker genes in healthy leaves , we found variation between the Solanum clones in constitutive mRNAs levels of the pathogenesis-related ( PR ) genes PR-1 , PR-2 , and PR-5 . At the genus level, there was no correlation between basal PR mRNA levels and nonspecific resistance to P.&nbsp;infestans . In contrast, a positive correlation was found at the species level in S.&nbsp;arnezii x hondelmannii , S.&nbsp;microdontum , S.&nbsp;sucrense and S.&nbsp;tuberosum . In S.&nbsp;tuberosum cultivars, the levels of PR gene expression were the highest in resistant 'Robijn', intermediate in partially resistant 'Première', 'Estima' and 'Ehud', and the lowest in susceptible 'Bintje'. These results suggest that constitutive expression of PR genes may contribute to nonspecific resistance to P.&nbsp;infestans in Solanum . Therefore, PR mRNA levels could serve as molecular markers in potato breeding programs.In conclusion, diverse resistance reactions to P.&nbsp;infestans operate at various levels in Solanum species, including specific and nonspecific mechanisms. The ubiquitous association of the HR in all types of resistance suggests that numerous R genes are present in Solanum against the oomycete P.&nbsp;infestans . A remaining challenge is the identification and transfer of these R genes into commercially grown potato cultivars.

Ever since the late blight epidemics of the mid-nineteenth century, man has endeavored to protect his potato crop. Every year, extensive chemical protection is applied, which is expensive and may be harmful to the natural environment. The use of resistant potato cultivars would provide an elegant alternative, however breeding for late blight resistance has not yet resulted in adequately resistant cultivars. In addition to the demand for a high level of resistance, the resistance should be durable. The causal agent of the late blight disease is Phytophthora infestans , a biotrophic oomycete pathogen. Oomycetes are often incorrectly referred to as fungi, but they evolved the ability to infect plants independently from fungi, and may therefore have distinct mechanisms for interacting with plants. Insight in the mechanisms of resistance to P.&nbsp;infestans may assist the breeders in their operation to achieve durable resistance.Genetic resistance can be determined at the subspecies or variety level (race-specific resistance), or at the species or genus level (nonhost resistance). Nonhost resistance is full resistance, and is present in most plant species. In addition, resistance may be a quantitative trait (partial resistance). A rich pool of diverse resistances to P.&nbsp;infestans has been found in wild Solanum species, with levels ranging from full resistance to various levels of partial resistance. Some old potato cultivars also exhibit partial resistance, which proved to be durable. To achieve a durable late blight resistance, a better understanding of the molecular basis of the various types of resistances is essential. To this end, we compiled a set of Solanum species with various types and levels of resistance to P.&nbsp;infestans , and studied the cellular and molecular aspects of the resistance mechanisms present in these plants.Laboratory studies at the cellular and molecular level require an experimental assay, which is both comparable to the natural situation, and assures a high percentage of successful infections. To this end, we developed a resistance assay with detached leaves under controlled conditions in the laboratory and compared this assay with a field trial. The tested growing conditions of the plants did not affect the resistance to P.&nbsp;infestans. Leaves on intact plants however, were more resistant than detached leaves. The incubation conditions of the detached leaves in the laboratory assay rather than the detachment itself appeared to affect the resistance expression. However, on intact plants the infection frequency was too low for molecular studies. Since the ranking of resistance levels within a set of twenty plant clones was similar under laboratory and field conditions, the laboratory assay proved adequate to study the Solanum - P.&nbsp;infestans interaction.A cytological survey of the interaction between twenty Solanum clones and three P.&nbsp;infestans isolates provided the first impression of the nature of the resistance responses. Potato cultivars with race-specific resistance ( R ) genes displayed the hypersensitive response (HR), a programmed cell death of plant cells, upon inoculation with P.&nbsp;infestans . Through this rapid cell death, the biotrophic pathogen became localized between dead cells, and was prevented from further growth. Also durably resistant potato cultivars without known R genes, wild Solanum species, and nonhosts displayed the HR. Interestingly, in highly resistant Solanum species such as S. berthaultii and S&nbsp;circaeifolium, and nonhosts such as Arabidopsis thaliana and S.&nbsp;nigrum (black nightshade), the HR was extremely fast and effective, resulting in very localized cell death. In partially resistant plants, the HR was delayed, and resulted in larger HR lesions. Occasionally, hyphae were able to escape from these lesions and established a biotrophic interaction with the host. The effectiveness of the HR in restricting growth of the pathogen differed considerably between clones, and correlated with resistance levels. In addition to the HR, local depositions of callose and phenolic compounds occurred, which may function as physical barriers. Although these responses did not correlate with resistance levels, they may influence the balance between growth of the pathogen and induction of the HR. Ultimately, this fine balance may determine resistance at the cellular level, and illustrates the quantitative nature of the resistance to P.&nbsp;infestans at the plant or field level .The HR is initiated upon recognition of pathogen elicitors by plant cell receptors or R gene products as suggested by the gene-for-gene hypothesis. Several types of R genes are recognized in plants, including the nucleotide binding site leucine-rich repeat (NBS-LRR) type, and the Pto-like serine/threonine protein kinase type. The Pto gene was originally identified from wild relatives of tomato. We exploited our Solanum collection to identify Pto -like sequences, and studied evolutionary scenarios for Pto -like genes. Polymerase chain reaction (PCR) amplifications using primers based on conserved and variable regions of Pto yielded 32 intact Pto -like sequences from six Solanum species, and revealed an extensive Pto family. Pto -like transcripts were also detected in leaf tissue of all tested plants. The kinase consensus and autophosphorylation residues were highly conserved, in contrast to the kinase activation domain which is involved in ligand recognition in Pto. Phylogenetic analyses distinguished nine classes of Pto -like genes, and revealed that orthologues (homologues separated by a speciation process) were more similar than paralogues (homologues generated by a gene duplication event). This suggests that the Pto gene family evolved through a series of ancient gene duplication events prior to speciation in Solanum . The phylogenetic data are in line with recent results on the NBS-LRR class of R genes, and suggest that Pto- like genes are ancient, and highly diverse.Various levels of nonspecific resistance were revealed in Solanum species after inoculation with five P.&nbsp;infestans isolates. In partially resistant plants where hyphal escape occurred, the lesions expanded often slower than in susceptible plants. Here, defense mechanisms other than HR are thought to operate; this might for example involve systemic acquired resistance (SAR). SAR can be induced by various signals, but also basal levels of SAR may vary between plants. When we monitored basal expression levels of SAR marker genes in healthy leaves , we found variation between the Solanum clones in constitutive mRNAs levels of the pathogenesis-related ( PR ) genes PR-1 , PR-2 , and PR-5 . At the genus level, there was no correlation between basal PR mRNA levels and nonspecific resistance to P.&nbsp;infestans . In contrast, a positive correlation was found at the species level in S.&nbsp;arnezii x hondelmannii , S.&nbsp;microdontum , S.&nbsp;sucrense and S.&nbsp;tuberosum . In S.&nbsp;tuberosum cultivars, the levels of PR gene expression were the highest in resistant 'Robijn', intermediate in partially resistant 'Première', 'Estima' and 'Ehud', and the lowest in susceptible 'Bintje'. These results suggest that constitutive expression of PR genes may contribute to nonspecific resistance to P.&nbsp;infestans in Solanum . Therefore, PR mRNA levels could serve as molecular markers in potato breeding programs.In conclusion, diverse resistance reactions to P.&nbsp;infestans operate at various levels in Solanum species, including specific and nonspecific mechanisms. The ubiquitous association of the HR in all types of resistance suggests that numerous R genes are present in Solanum against the oomycete P.&nbsp;infestans . A remaining challenge is the identification and transfer of these R genes into commercially grown potato cultivars.