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Numerous pathogens can infect potato, but late blight (Phytophthora infestans (Mont.) de Bary) and potato cyst nematodes (PCN) Globodera rostochiensis and G. pallida are most damaging. Several species of root knot nematodes (RKN) are an emerging threat. Breeders have successfully deployed disease resistance genes (R-genes) to protect potato from diseases, starting from the first half of the 20th century. DNA markers facilitate the introgression of R-genes and enable the pyramiding of multiple R-genes in a potato cultivar. Pyramiding may improve the level of resistance, the resistance spectrum and the durability of the resistance. In this thesis, the experimental work is described in four chapters. Two chapters focus on the identification, mapping and characterisation of late blight and nematode resistance genes. The other two chapters focus on the pyramiding of R-genes to achieve something more in terms of resistance than was offered by the individual R-genes. In Chapter 2, a locus involved in late blight resistance, derived from Solanum microdontum, was identified and characterised. The resistance is associated with a hypersensitive response and results in a delay of infection of about 1-2 weeks. Both a quantitative as well as a qualitative genetic approach was used, based on data from a field assay. QTL analysis identified a QTL on chromosome 4. A qualitative genetic analysis resulted in the positioning of this locus on the short arm of chromosome 4. This position coincides with a conserved Phytophthora R-gene cluster which includes R2, R2-like, RPi-blb3 and RPi-abpt. This strongly suggests that RPi-mcd1 is the fifth R-gene of this NBS-LRR cluster. In Chapter 3, two resistance genes, RPi-mcd1 and RPi-ber, introgressed from the wild tuber bearing potato species S. microdontum and S. berthaultii were combined in a segregating diploid S. tuberosum population. Individual genotypes from this segregating population were classified into four groups by means of flanking molecular markers; carrying no R-gene, with only RPi-mcd1, with only RPi-ber, and a group with the pyramided RPi-mcd1 and RPi-ber. The levels of resistance between the groups were compared in a field experiment in 2007. The group with RPi-mcd1 showed a significant delay to reach 50% infection of the leaf area of three days. The group with RPi-ber showed a delay of three weeks. The resistance level in the pyramid group suggested an additive effect of RPi-mcd1 with RPi-ber. This result suggests that potato breeding can benefit from combining individual R-genes. In Chapter 4, a resistance to G. pallida Rookmaker (Pa3), originating from wild species S. tarijense was identified by QTL analysis. The resistance could largely be ascribed to one major QTL. GpaXIltar explained 81.3 % of the phenotypic variance in the disease test and mapped to the long arm of chromosome 11. Another minor QTL explained 5.3 % of the phenotypic variance and mapped to the long arm of chromosome 9. Clones containing both QTL showed no lower cyst counts than clones with only GpaXIltar. After Mendelising the phenotypic data, GpaXIltar could be more precisely mapped near markers GP163 and FEN427 thus anchoring GpaXIltar to a region with a known R-gene cluster containing virus and nematode resistance genes. In Chapter 5, a study is described that tests if pyramiding of two resistance genes against the root knot nematode Meloidogyne hapla, RMh-tar and RMh-chcA , will result in improved, or even an absolute level of resistance. RMh-tar and RMh-chcA, introgressed from the wild tuber bearing potato species Solanum tarijense and S. chacoense were combined in a segregating diploid S. tuberosum population. With the aid of markers, descendants from this segregating population were classified into four groups, carrying no R-gene, with only RMh-tar, with only RMh-chcA, and a group with the pyramided RMh-tar and RMh-chcA. Upon inoculation with M. hapla isolate Bovensmilde, the group containing only RMh-chcA showed a decline of 88 % in average developed egg masses compared to the group without RMh-chcA and RMh-tar. The group of genotypes containing only RMh-tar, but not RMh-chcA, showed a decline of 55% in developed egg masses compared to the group without RMh-chcA and RMh-tar. The effect of both loci, RMh-tar and RMh-chcA combined, did not further reduce the number of egg masses compared to the level of RMh-chcA alone. The study presented in this thesis shows that marker assisted selection is a very powerful method and sometimes the only way to screen for the presence of certain genes. It furthermore shows that pyramiding different resistance genes, even with minor effects, can result in plants with an increased level of resistance.

Two main methods in sustainable pest control are host plant resistance and biological control. These methods have been developed in isolation. However, host plant characteristics can decisively affect the effectiveness of biological control agents, and therefore when altering plant characteristics in a breeding programme, the implications for biological control should be studied as well. Moreover, this may also provide the opportunity to breed for plants that are optimally compatible with biological control agents. Breeding for host plant resistance has a long history. However, in the past decades a new development was to use transgenes to generate plants resistant to pests and diseases. In more recent years also Plant genetic engineering makes it possible to transfer a foreign gene to a host plant to introduce resistance against insects or to produce a volatile which can attract the natural enemy of the pest after the host plant is wounded by insect herbivores. In this thesis I have modified direct and indirect defence to herbivores in Arabidopsis plants through a transgenic approach. In order to evaluate transgenic Arabidopsis with different genes that influence direct and indirect defence to the herbivore Plutella xylostella (diamondback moth, DBM). I investigated the effect of a protease inhibitor from mustard plants (Mustard Trypsin Inhibitor 2, MTI2). MTI-2 transgenic Arabidopsis did not affect the performance of a Dutch and a Chinese strain of DBM. My data show that the gut enzymes of DBM are insensitive to MTI2, which can be explained by the specific inactivation of MTI2. DBM has apparently developed MTI2 inactivation as a way to protect itself against this protease inhibitor. This makes ecological sense as MTI2 is part of the defense of its brassicaceous host plants. Terpenoids are among the plant volatiles involved in indirect defence of many plant species. I exploited the availability of a linalool synthase (LIS) gene to develop transgenic herbivore-inducible linalool-producing Arabidopsis plants and developed Arabidopsis plants with this linalool synthase gene under the protease inhibitor 2 (PI2) promoter from potato. As a result the linalool synthase was inducible by methyl jasmonate application, but not by P. xylostella infestation. To investigate a transgenic approach to combining direct and indirect defence, a gene encoding a Bt toxin and a gene encoding linalool synthase were integrated into Arabidopsis as a model. The data show that hybrid lines carrying Bt and LIS genes in Arabidopsis combine toxicity to the DBM larvae (due to Bt) and repellence to the adults of DBM (due to linalool). Moreover, the linalool emission also affected parasitoid behaviour when the plants were damaged. DBM-infested dual transgenic plants were more attractive to the parasitoid D. semiclausum than undamaged dual transgenic plants, but less attractive than DBM-infested untransformed plants. The percentage parasitization of DBM larvae on transgenic plants was not affected by the transgenes. In conclusion, my data provide interesting options for the development of transgenic crops that interfere with the biology of pests and enhance the effectiveness of the pest’s natural enemies. In this way transgenic crops that integrate host plant resistance with biological control may be developed.

The aphidMyzuspersicae(Sulzer) constitute a threat to potato crops because of their efficiency to transmit viruses. Many wildSolanumspecies have been reported to have resistance to M.persicae . These species represent an important potential source of resistance, which can be used to enhance resistance in crops. The aim of this thesis was to find and study in tuber bearingSolanumspecies different mechanisms of resistance to M.persicae that also would reduced the spread of viruses. Resistance and susceptibility of wildSolanumgenotypes and cultivated potatoes were characterized and linked to plant-aphid interactions with respect to aphid behaviour and performance and plant responses to aphid attack. A combination of aphid colony-development assay with the study of probing activities was used to localize resistance factors in tissues ofSolanumgenotypes. Genotypes with different degrees of resistance were found. S.stoloniferum showed pre-phloem resistance to M.persicae, and hence it was used as a model plant to unravel and characterisephenotypicallyand at molecular level the interactions of a single plant with different aphid species. Aphid performance, settling behaviour, and probing studies of M.persicae andMacrosiphumeuphorbiae (Thomas) on S.stoloniferum showed that while S.stoloniferum could be a host plant for M.euphorbiae , it is a poor host for M.persicae .The resistance found in S.stoloniferum against M.persicae seems to rely on constitutively expressed physical traits with some age effects.The transcriptional response of S.stoloniferum to the attack of M.euphorbiae (compatible interactions) was stronger than in response to M.persicae (incompatible). This stronger response to M.euphorbiae involves up-regulation of genes related to pathogenesis (PR), regulatory, and protein metabolism and down-regulation of regulatory genes, general metabolism and photosynthesis related genes.Infestation of S.stoloniferum leaves with M.persicae aphids leads to the development of pustules. Microscopic analysis of the pustules showed a burst of tissue on the surrounding of the vascular bundle. In contrast, the infestation with M.euphorbiae did not induce any visible cellular changes. The formation of pustules and the induction of some genes in S.stoloniferum suggest that a similar situation might exist between plants-pathogenic bacteria interactions, and plants-aphids interactions.Response of S.tuberosumcv.Kardalto the attack of M.persicae was evaluated by studying gene expression. The plant responses depend on foliage maturity. Young leaves ofcv.Kardalare resistant to M.persicae whereas mature to senescent leaves are susceptible. In old leaves M.persicae attack elicits higher number of differentially regulated genes than in young leaves.The transcriptional results obtained with the two systems: (1) S.stoloniferum after the attack of M.persicae and M.euphorbiae , and (2) S.tuberosumcv.Kardalat different maturity leaf stages after the attack of M.persicae were compared. The gene-expression studies provide evidence that S.tuberosum and S.stoloniferum respond by activating the salicylic acid (SA) and ethylene (ET) pathways. Genes responsive tojasmonicacid were differentially regulated in low number in the S.stoloniferum - M.euphorbiae but not in thecv.Kardal- M.persicae interaction.At the local level a compatible plant-aphid interaction resulted in a broader gene expression response than that a systemic level. Genes were identified related to changes in sink-source relationship at the feeding site which may indicate a plant manipulation by the aphids related to the process of changing the physiological status of the tissue towards a local metabolic sink; also genes related to signal-transduction pathways, regulation and signalling, protein metabolism, maintenance of cell homeostasis, transport, secondary metabolism, and structural features were found to be differentially regulated. On the contrary, in incompatible interactions the transcriptional response of the plant seems to be more restricted.PLRV-infection in potato plants ofcv.Kardalwas found to affect aphid behaviour. M.persicae responses to volatiles emitted from PLRV-infected and non-infected plants depend on the age of the leaf. PLRV infection affects also the probing behaviour of M.persicae . On virus-infected plantsstyletpenetration into the plant tissue is enhanced. The transmission efficiency of PLRV is also expected to be affected in PLRV-infected plants because these plants attract more aphids than non-infected plants.The results obtained on this research (e.g., aphid performance, probing behaviour, colony development, settling behaviour, and gene expression analysis ofSolanumspp. attacked by aphids) contribute to the understanding of plant responses towards aphid attack as a basis for further unravelling the resistance mechanisms at the metabolic, molecular, and genetic levels.

Begin 2005 verzocht de interdepartementale Commissie Biotechnologie Wageningen UR een onderzoeksprogramma op te stellen voor een perspectiefvol GMO-project. Dit met het oog op de Nederlandse innovatieagenda en behoud of vergroting van de concurrentiekracht van de Nederlandse economie. Uitgangspunt daarbij was de Integrale Nota Biotechnologie (2000) met als centraal motto het verantwoord en zorgvuldig benutten van kansen ten behoeve van economie en duurzame landbouw. De keuze viel op een 'proof of principle' project van een duurzaam Phytophthoraresistente aardappel vanwege de economische aspecten zoals de kosten van beheersing van de ziekte en het veiligstellen van de winstgevendheid van de pootgoedsector. Milieuaspecten zoals reductie van de emissie van chemicaliën en een verminderd energiegebruik voor de toediening telden eveneens mee alsook het vergroten van de wetenschappelijk innovatiekracht

De opzet van het paprikarassenonderzoek verschilde sterk van opzet in vergelijking met andere jaren. In 2007 participeerden veredelingsbedrijven en telers in het onderzoek. De nieuwe rassen voor de teelt van rode paprika produceerden allemaal meer dan het standaard ras, maar ze vertonen ook mankementen. In tabel de beoordelingen, resistentie, productie, smaak en houdbaarheid

The aphidMyzuspersicae(Sulzer) constitute a threat to potato crops because of their efficiency to transmit viruses. Many wildSolanumspecies have been reported to have resistance to M.persicae . These species represent an important potential source of resistance, which can be used to enhance resistance in crops. The aim of this thesis was to find and study in tuber bearingSolanumspecies different mechanisms of resistance to M.persicae that also would reduced the spread of viruses. Resistance and susceptibility of wildSolanumgenotypes and cultivated potatoes were characterized and linked to plant-aphid interactions with respect to aphid behaviour and performance and plant responses to aphid attack. A combination of aphid colony-development assay with the study of probing activities was used to localize resistance factors in tissues ofSolanumgenotypes. Genotypes with different degrees of resistance were found. S.stoloniferum showed pre-phloem resistance to M.persicae, and hence it was used as a model plant to unravel and characterisephenotypicallyand at molecular level the interactions of a single plant with different aphid species. Aphid performance, settling behaviour, and probing studies of M.persicae andMacrosiphumeuphorbiae (Thomas) on S.stoloniferum showed that while S.stoloniferum could be a host plant for M.euphorbiae , it is a poor host for M.persicae .The resistance found in S.stoloniferum against M.persicae seems to rely on constitutively expressed physical traits with some age effects.The transcriptional response of S.stoloniferum to the attack of M.euphorbiae (compatible interactions) was stronger than in response to M.persicae (incompatible). This stronger response to M.euphorbiae involves up-regulation of genes related to pathogenesis (PR), regulatory, and protein metabolism and down-regulation of regulatory genes, general metabolism and photosynthesis related genes.Infestation of S.stoloniferum leaves with M.persicae aphids leads to the development of pustules. Microscopic analysis of the pustules showed a burst of tissue on the surrounding of the vascular bundle. In contrast, the infestation with M.euphorbiae did not induce any visible cellular changes. The formation of pustules and the induction of some genes in S.stoloniferum suggest that a similar situation might exist between plants-pathogenic bacteria interactions, and plants-aphids interactions.Response of S.tuberosumcv.Kardalto the attack of M.persicae was evaluated by studying gene expression. The plant responses depend on foliage maturity. Young leaves ofcv.Kardalare resistant to M.persicae whereas mature to senescent leaves are susceptible. In old leaves M.persicae attack elicits higher number of differentially regulated genes than in young leaves.The transcriptional results obtained with the two systems: (1) S.stoloniferum after the attack of M.persicae and M.euphorbiae , and (2) S.tuberosumcv.Kardalat different maturity leaf stages after the attack of M.persicae were compared. The gene-expression studies provide evidence that S.tuberosum and S.stoloniferum respond by activating the salicylic acid (SA) and ethylene (ET) pathways. Genes responsive tojasmonicacid were differentially regulated in low number in the S.stoloniferum - M.euphorbiae but not in thecv.Kardal- M.persicae interaction.At the local level a compatible plant-aphid interaction resulted in a broader gene expression response than that a systemic level. Genes were identified related to changes in sink-source relationship at the feeding site which may indicate a plant manipulation by the aphids related to the process of changing the physiological status of the tissue towards a local metabolic sink; also genes related to signal-transduction pathways, regulation and signalling, protein metabolism, maintenance of cell homeostasis, transport, secondary metabolism, and structural features were found to be differentially regulated. On the contrary, in incompatible interactions the transcriptional response of the plant seems to be more restricted.PLRV-infection in potato plants ofcv.Kardalwas found to affect aphid behaviour. M.persicae responses to volatiles emitted from PLRV-infected and non-infected plants depend on the age of the leaf. PLRV infection affects also the probing behaviour of M.persicae . On virus-infected plantsstyletpenetration into the plant tissue is enhanced. The transmission efficiency of PLRV is also expected to be affected in PLRV-infected plants because these plants attract more aphids than non-infected plants.The results obtained on this research (e.g., aphid performance, probing behaviour, colony development, settling behaviour, and gene expression analysis ofSolanumspp. attacked by aphids) contribute to the understanding of plant responses towards aphid attack as a basis for further unravelling the resistance mechanisms at the metabolic, molecular, and genetic levels.

Potato (Solanum tuberosum ssp. tuberosum) is the fourth most important food crop with an annual yield of about 300 million tons over the world. The history of the domestication of potato shows that disease-causing agents followed the tracks of potato cultivation in temperate climates across continents, resulting in substantial crop losses. Plants including potato have evolved defence mechanisms against pathogens, of which the pathotype-specific system involving resistance genes (R genes) is very effective. In search for durable resistance in crop plants, an increasing number of R genes has been identified and characterized, providing valuable information on their genomic organisation and evolutionary dynamics. They are often located in R gene clusters on complex loci or so called ‘hotspots’ for resistance in the plant genome. The evolution of host pathogen-interactions based on gene-for-gene interactions has been described in two prevailing theories. The arms race hypothesis assumes that new R gene alleles continuously emerge in a plant population and replace resistance alleles that are overcome by the pathogen. A short lifespan is postulated for a particular R gene allele. More recent, the ‘trench warfare’-model is proposed to explain the dynamics of R genes and Avr genes as repeated advances and retreats of resistance and virulence alleles. This frequency dependent selection pressure results in the maintenance of resistance alleles as balanced polymorphisms in natural populations over long periods of time (long lifespan). The aim of the research described in this thesis was to study the molecular mechanisms underlying the evolution of R gene recognition specificities using the virus resistance gene Rx1 from potato. Rx1 and its close homologue Gpa2 are both located in a single R gene cluster of about 110 kB on chromosome XII in potato and share an overall homology in the amino acid sequence of about 87%. Interestingly, these two R genes confer resistance to taxonomically unrelated pathogens, a virus and a nematode. However, Rx1 results in extreme resistance to potato virus X (PVX), whereas Gpa2 gives a much slower and milder resistance response to the potato cyst nematode Globodera pallida. The Rx1/Gpa2 resistance cluster was analysed on three S. tuberosum ssp. tuberosum haplotypes derived from the diploid potato clones SH and RH, homeologous to the resistant S. tuberosum ssp. andigena haplotype of SH, which resulted in the identification of nine additional homologues of Rx1 and Gpa2 in this region. In postulating a long lifespan for Rx, the findings of functional orthologues from distant related Solanum species give support for the trench warfare hypothesis. A survey across 35 species from the genus Solanum resulted in the identification of two novel functional orthologues of the disease resistance gene Rx1 in the wild potato species S. lepthophyes/sparsipilum and S. albicans, Rx3 and Rx4. By functional assays it was shown, that Rx3 and Rx4 confer Rx-mediated resistance to PVX in the corresponding S. lepthophyes/sparsipilum and S. albicans genotypes. Our finding of Rx3 and Rx4, together with Rx1 from S. tuberosum ssp. andigena and Rx2 from S. acaule, represents the first example of functional orthologues from the class of NBS-LRR resistance genes in four different plant species. Subsequent screening of about 5000 genotypes derived from 1000 accessions across 200 Solanum species resulted in the identification of 14 additional distantly related Solanum species harbouring Rx candidate genes, which shows that the Rx orthologues are of ancient origin and derived from one ancestral gene. This indicates that Rx mediated PVX recognition arose before the groups of Tuberosa (Peru) and Acaule/Demissum diverged. To gain more insight in the structural and evolutionary relationship of the resistance gene cluster a set of 75 Rx1/Gpa2 homologues was obtained from 10 different Solanum species, including the four functional orthologous virus resistance genes Rx1-4, the truncated Rxedn that harbours Rx resistance specificity and the nematode resistance gene Gpa2. About one third of the homologues were found to encode for a protein harbouring complete CC-, NBS- and LRR- domains analogous to Rx and Gpa2, indicating the presence of functional R genes with unknown specificities. We identified a local structural variability in the sequence region encoding LRR10, dividing the homologues in 3 structural subclasses. The occurrence of similar sequence exchange tracks in homologues isolated from different Solanum species indicates that interallelic exchanges took place before speciation. Analysis for positive selection revealed very significant positive selection on codon sites within the LRR domain, but also within the CC- and NBS- domain. In addition, the genomic organisation of the Rx1/Gpa2 cluster was analysed. Therefore, sequence analysis was carried out on several BAC clones derived from S. tuberosum ssp. andigena, S. tuberosum ssp. tuberosum and S. lepthophyes/sparsipilum harbouring in total 17 Rx1/Gpa2 homologues, including the functional resistance genes Rx1 and Gpa2 from potato. The homeologous chromosomal regions derived from S. tuberosum ssp. andigena and S. tuberosum ssp. tuberosum were assembled and aligned based on syntenic regions. However, comparative sequence analysis revealed large intergenic sequence divergence in this region, which was increasing for more distant related Solanum species. The occurrence of a family of conserved genes with homology to RING zink-finger protein encoding genes in vicinity of the Rx/Gpa2 homologues suggests that tandem duplication of these genes has occurred at this locus. The major results described in this thesis are discussed and an outlook on structure-function analyses of Rx1 and Gpa2 is presented.

Potato (Solanum tuberosum ssp. tuberosum) is the fourth most important food crop with an annual yield of about 300 million tons over the world. The history of the domestication of potato shows that disease-causing agents followed the tracks of potato cultivation in temperate climates across continents, resulting in substantial crop losses. Plants including potato have evolved defence mechanisms against pathogens, of which the pathotype-specific system involving resistance genes (R genes) is very effective. In search for durable resistance in crop plants, an increasing number of R genes has been identified and characterized, providing valuable information on their genomic organisation and evolutionary dynamics. They are often located in R gene clusters on complex loci or so called ‘hotspots’ for resistance in the plant genome. The evolution of host pathogen-interactions based on gene-for-gene interactions has been described in two prevailing theories. The arms race hypothesis assumes that new R gene alleles continuously emerge in a plant population and replace resistance alleles that are overcome by the pathogen. A short lifespan is postulated for a particular R gene allele. More recent, the ‘trench warfare’-model is proposed to explain the dynamics of R genes and Avr genes as repeated advances and retreats of resistance and virulence alleles. This frequency dependent selection pressure results in the maintenance of resistance alleles as balanced polymorphisms in natural populations over long periods of time (long lifespan). The aim of the research described in this thesis was to study the molecular mechanisms underlying the evolution of R gene recognition specificities using the virus resistance gene Rx1 from potato. Rx1 and its close homologue Gpa2 are both located in a single R gene cluster of about 110 kB on chromosome XII in potato and share an overall homology in the amino acid sequence of about 87%. Interestingly, these two R genes confer resistance to taxonomically unrelated pathogens, a virus and a nematode. However, Rx1 results in extreme resistance to potato virus X (PVX), whereas Gpa2 gives a much slower and milder resistance response to the potato cyst nematode Globodera pallida. The Rx1/Gpa2 resistance cluster was analysed on three S. tuberosum ssp. tuberosum haplotypes derived from the diploid potato clones SH and RH, homeologous to the resistant S. tuberosum ssp. andigena haplotype of SH, which resulted in the identification of nine additional homologues of Rx1 and Gpa2 in this region. In postulating a long lifespan for Rx, the findings of functional orthologues from distant related Solanum species give support for the trench warfare hypothesis. A survey across 35 species from the genus Solanum resulted in the identification of two novel functional orthologues of the disease resistance gene Rx1 in the wild potato species S. lepthophyes/sparsipilum and S. albicans, Rx3 and Rx4. By functional assays it was shown, that Rx3 and Rx4 confer Rx-mediated resistance to PVX in the corresponding S. lepthophyes/sparsipilum and S. albicans genotypes. Our finding of Rx3 and Rx4, together with Rx1 from S. tuberosum ssp. andigena and Rx2 from S. acaule, represents the first example of functional orthologues from the class of NBS-LRR resistance genes in four different plant species. Subsequent screening of about 5000 genotypes derived from 1000 accessions across 200 Solanum species resulted in the identification of 14 additional distantly related Solanum species harbouring Rx candidate genes, which shows that the Rx orthologues are of ancient origin and derived from one ancestral gene. This indicates that Rx mediated PVX recognition arose before the groups of Tuberosa (Peru) and Acaule/Demissum diverged. To gain more insight in the structural and evolutionary relationship of the resistance gene cluster a set of 75 Rx1/Gpa2 homologues was obtained from 10 different Solanum species, including the four functional orthologous virus resistance genes Rx1-4, the truncated Rxedn that harbours Rx resistance specificity and the nematode resistance gene Gpa2. About one third of the homologues were found to encode for a protein harbouring complete CC-, NBS- and LRR- domains analogous to Rx and Gpa2, indicating the presence of functional R genes with unknown specificities. We identified a local structural variability in the sequence region encoding LRR10, dividing the homologues in 3 structural subclasses. The occurrence of similar sequence exchange tracks in homologues isolated from different Solanum species indicates that interallelic exchanges took place before speciation. Analysis for positive selection revealed very significant positive selection on codon sites within the LRR domain, but also within the CC- and NBS- domain. In addition, the genomic organisation of the Rx1/Gpa2 cluster was analysed. Therefore, sequence analysis was carried out on several BAC clones derived from S. tuberosum ssp. andigena, S. tuberosum ssp. tuberosum and S. lepthophyes/sparsipilum harbouring in total 17 Rx1/Gpa2 homologues, including the functional resistance genes Rx1 and Gpa2 from potato. The homeologous chromosomal regions derived from S. tuberosum ssp. andigena and S. tuberosum ssp. tuberosum were assembled and aligned based on syntenic regions. However, comparative sequence analysis revealed large intergenic sequence divergence in this region, which was increasing for more distant related Solanum species. The occurrence of a family of conserved genes with homology to RING zink-finger protein encoding genes in vicinity of the Rx/Gpa2 homologues suggests that tandem duplication of these genes has occurred at this locus. The major results described in this thesis are discussed and an outlook on structure-function analyses of Rx1 and Gpa2 is presented.

PRI en LBI onderzoeken in een project hoe resistentie tegen trips overerft. Maar er zijn meer eigenschappen belangrijk voor de weerbaarheid van de plant tegen trips. Zo blijken vroegheid en het tijdstip van planten een rol te spelen, evenals de dikte van de waslaag op de kool

An important question in plant defense signaling research is: how are plants capable of integrating signals induced by pathogenic micro-organisms and herbivorous insects into defenses that are specifically active against the attacker encountered? Plant defenses against pathogens and insects are differentially regulated by cross-communicating signaling pathways in which salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) play key roles. To understand how plants integrate pathogen- and insect-induced signals into specific defense responses, we monitored the dynamics of SA, JA, and ET signaling and genome-wide transcriptome changes in Arabidopsis after attack by a set of microbial pathogens and herbivorous insects with different modes of attack. Arabidopsis plants were exposed to a pathogenic leaf bacterium ( Pseudomonas syringae pv. tomato ), a pathogenic leaf fungus ( Alternaria brassicicola ), tissue-chewing caterpillars ( Pieris rapae ), cell-content-feeding thrips ( Frankliniella occidentalis ), or phloem-feeding aphids ( Myzus persicae ). Monitoring the signal signature in each plant-attacker combination showed that the kinetics of SA, JA, and ET production varies greatly in both quantity and timing. The transcriptional alterations were predominantly attacker-specific, but the processes affected surprisingly similar. This indicates that the different attackers induce changes in similar plant processes through largely non-overlapping transcriptional alterations. Yet, infestation by M. persicae induced a transcriptional response that was opposite to those induced by the other attackers or exogenous application of MeJA. We concluded that SA, JA, and ET play a primary role in the orchestration of the plant's defense response, but other regulatory mechanisms, such as pathway cross-talk and additional attacker-induced signals, eventually shape the highly complex attacker-specific defense response.Little is known about the spectrum of effectiveness of the different types of induced resistance that are expressed upon attack by pathogens or insects. Because the signaling pathways that control induced resistance against pathogens and insects partly overlap, we decided to investigate the effectiveness of microbially induced resistance against the tissue-chewing herbivorous insects Pieris rapae and Spodoptera exigua in Arabidopsis. Two types of microbially induced resistance were studied: systemic acquired resistance (SAR), which is induced upon predisposal infection by necrotizing pathogens, and rhizobacteria-mediated induced systemic resistance (ISR), which is triggered by selected strains of non-pathogenic, root-colonizingrhizobacteria. No effect of SAR or ISR was evident on herbivore-induced attractiveness of the parasitic wasp Cotesia rubecula , indicating that neither type of induced resistance influenced indirect defense against these insects. In feeding experiments on whole plants, induction of SAR and ISR significantly reduced growth and development of the generalist herbivore S. exigua , whereas the performance of the specialist P. rapae was unaffected. The JA- and ET-responsive genes PDF1.2 and HEL , which were activated upon feeding by either of the two herbivores, showed a strongly potentiated expression pattern in SAR- and ISR-expressing plants upon feeding by S. exigua , but not upon feeding by P. rapae .This differential priming for enhanced herbivore-induced gene expression was confirmed in microarray experiments using a dedicated cDNA microarray containing 111 insect-responsive Arabidopsis genes. These results suggest that the effectiveness of microbially induced SAR and ISR against S. exigua feeding is associated with priming for enhanced defense-related gene expression.In conclusion, this thesis highlights the complexity of the defense signaling interactions between plants, pathogens and insect herbivores.

Er zijn zes nieuwe biologische aardappelrassen gepresenteerd die resistent zijn tegen phytophthora.

The development of potato varieties with resistance towards the potato cyst nematode, allowed a dramatic decrease of the use of nematicides. Subsequently the population of the free living nematodes and the root-knot nematodes ( Meloidogyne spp.) has increased. Among the root-knot nematodes, three Meloidogyne species are important in the potato cultivation in The Netherlands: M. hapla , M. chitwoodi and M. fallax . The latter two species are the most harmful because they cause malformation in the tubers and are quarantine organisms. Until now no resistant potato cultivars are available. Several wild species of potato show resistance, but several back crossings are required to develop a root-knot nematode resistant potato cultivar. Selection based on molecular markers will speed up this development and will replace the expensive and time consuming bioassays, which have to be carried out under strict quarantine conditions. In this thesis diploid as well as polyploid wild Solanum species are used for the introgression of resistance genes in cultivated potato, and to analyse the inheritance of the various resistances.Chapter 2 describes the genetic analysis of the diploid wild species Solanum chacoense with resistance against M. hapla and M. fallax. An AFLP based linkage map was constructed, resulting in twelve linkage groups of either parent of the mapping population with a total length of 685 and 596 cM each. Due to the large differences in AFLP patterns between S. chacoense and cultivated potato, chromosome numbers could not be assigned to the linkage groups containing the QTLs. Two QTLs for resistance against the M. hapla population Hi were identified in this population. These two QTLs, R Mh-chc A and R Mh-chc B , explained 38% and 13% of the total phenotypic variance of the resistance to M. hapla . As a consequence of the large variation in the results of the bioassay, phenotypic selection may lead to the loss of these resistance QTLs. This loss can be prevented by marker assisted selection with the markers flanking the QTLs. The genetic analysis of the resistance against M. fallax resulted in the detection of one QTL explaining 14% of the phenotypic variance. The high level of resistance to M. fallax as observed in the resistant parent was not observed in the progeny. In view of the modest results that can be expected from S. chacoense , we cannot recommend breeding efforts with this germplasm. Better results in genetic analyses and introgression of resistance against M. fallax were achieved in the mapping studies with the wild Solanum species S. fendleri (Chapter 5), S. hougasii and S. bulbocastanum (Chapter 6).The differential interaction of eight M. hapla populations to the resistance QTLs, R Mh-chc A and R Mh-chc B was studied in Chapter 3. The R Mh-chc A allele allows recognition on virulence factors present in all six tested cytological race A populations. Although the allele R Mh-chc B also showed a reduction in the amount of formed egg masses of population Ham, this allele had only an additive effect with population Hi, the population initially used for the QTL analysis (Chapter 2). No effect of both alleles was noticed for the two race B populations. Besides the distinctive difference in reproduction between race A and B, both races can now also be divided based on their differences in virulence to the R Mh-chc A allele. Furthermore, the molecular fingerprints allow too clearly distinguish between the races A and B. Because the resistant parent of the mapping population is susceptible to the race B populations, it is not worthwhile to check the used mapping population for other resistance QTLs. The breeder should therefore search for new sources of resistance to the race B populations in the wild species. Looking at the higher level of reproduction, the population Han would be the most appropriate population to be used in that survey.In Chapter 4 the diploid wild species S. tarijense was used as the source of resistance to M. hapla. The non absolute level of resistance and the continuous distribution of produced egg masses in the segregating offspring, suggests that the resistance is under polygenic control. Therefore a linkage map of the BC1 mapping population was developed as prerequisite of QTL analysis. The assignment of a chromosome number to the linkage groups was simple, because a detailed genetic map was already constructed of the susceptible parent. The linkage groups of the resistant female parent were subsequently aligned to the genetic map of the susceptible male parent using the AFLP markers that were heterozygous in both parents (so-called ab×ab markers). The QTL mapping approach resulted in only one locus, R Mh-tar , on chromosome 7. In contrast to QTL analysis that leads to a broad QTL interval, qualification of the resistance will lead to a more precise map position of the resistance locus. For that case the progeny of the mapping population was arbitrary classified in two groups: 1) a resistant group with the amount of less than1 egg mass and 2) a susceptible group with more than 10 egg masses. Via this approach the R Mh-tar resistance gene could be located on a distal position of the short arm of chromosome 7, and the low amount of singletons offered an indirect validation of the classification of the resistance phenotypes in discrete groups. The value of the R Mh-tar gene for the potato breeding is depending on the allele frequency of the associated virulence genes in the M. hapla populations and the geographic distribution of such populations.In contrast to the research with M. hapla as described in Chapter 2 and 4, the progeny of the mapping populations with resistance against M. chitwoodi and M. fallax (Chapter 5 and 6) could be easily classified as resistant or susceptible. This suggests that resistance is mediated by a single R-gene. The resistance against both nematode species, M. chitwoodi and M. fallax , was absolutely correlated in all three mapping populations, derived from S. fendleri (Chapter 5), S. hougasii and S. bulbocastanum (Chapter 6). In Chapter 5 the monogenic resistance against M. chitwoodi and M. fallax was mapped in an inter-specific and an intra-specific mapping population of the tetraploid wild species S. fendleri . By using the so-called Bulked Segregant Analysis (BSA) method, a large amount of closely linked markers was identified efficiently. In the intra-specific mapping population a remarkably lower amount of linked AFLP markers was found. This can be due to the fact that S. fendleri is a self-fertilising species, showing a lower level of genetic polymorphisms. On the other hand the genetic dissimilarity between the wild species introgression segments and the recurrent potato parents may have caused an elevated level of polymorphic markers in the BC 2 inter-specific mapping population. Besides the larger amount of polymorphic markers, the utilisation of inter-specific mapping populations is an advantage for the breeder, because back-crossings are already made, necessary to introgress the resistance into potato. Based on the sequence of an R Mc1-fen locus linked AFLP marker, a PCR marker was developed. This marker was used to map its position in a reference map, were it was located on the distal position of the long arm of chromosome 11. The chromosomal position of the R Mc1-fen locus was confirmed by using the chromosome 11 specific CAPS marker M39b. The R Mc1-fen gene is located in a cluster of resistance genes, containing the highly related Rmc1 gene and other fungus, virus and nematode resistance genes. This PCR marker, however, can not yet be used in marker assisted selection because 40% of the progeny with the PCR product will not contain the resistance allele.Chapter six describes the localisation of resistance against M. chitwoodi and M. fallax in a BC2 population of the hexaploid wild species S. hougasii . Also this study used the BSA method, resulting in a linkage group of 14 AFLP markers and the monogenic resistance locus R Mc1-hou . Similar to the linkage group of S. fendleri, the linkage group of S. hougasii has been positioned on the distal position of the long arm of chromosome 11.The differential interaction between the resistance genes R Mc1-blb , R Mc1-fen and R Mc1-hou with six M. chitwoodi populations has been studied. Differences in virulence were not found between race 1 and race 2, but, remarkably, within the two races. Populations Ccl and Cbh seem to have a similar virulence spectrum, while these populations are described as respectively race 1 and race 2. The presence of virulence in the populations will have a negative effect on the durability of the resistance. Because the three resistance genes against M. chitwoodi and M. fallax from the wild species S. bulbocastanum , S. fendleri and S. hougasii are mapped on the same locus and act against the same spectrum of virulence genes, no additional value is expect from the strategy of pyramiding these genes. Consequently, the breeder has to search for new resistance sources against the virulent nematode population Ccl and/or Cbh, in order to develop a potato with broad spectrum resistance.The resistance genes described in this thesis can be introgressed in potato with the help of molecular markers. Moreover the presence of individual resistance genes can be monitored by molecular markers, which is a prerequisite for pyramiding of R-genes. Pyramiding of the resistance genes may lead to a resistance with a broader spectrum, and/or may offer a more durable resistance, providing that it can be performed with loci with a complementary resistance spectrum.

De visie van Jan Velema van Vitalis op biologische zaadveredeling en het gebruik van biotechnologie. Hij is voor het gebruik van nieuwe technieken zoals merkers om raskenmerken te achterhalen. Maar een genenkaart inzetten om een nieuw gewas te maken, daar is hij geen voorstander van. Biologische veredeling richt zich op sterke planten met smaak en brede weerstand (partiële resistentie).

In dit rapport worden de mogelijkheden besproken om aaltjes in de biologische klaverteelt te beheersen door middel van resistente klaverrassen. Ook worden kort de mogelijkheden besproken van andere vlinderbloemige plantensoorten die geen last hebben van deze aaltjes en ze ook niet vermeerderen, zodat ze geschikt zijn om klavers te vervangen als groenbemester of als voedergewas. Beide oplossingsrichtingen blijken niet op korte termijn te kunnen bijdragen aan de beheersing van aaltjes

The development of potato varieties with resistance towards the potato cyst nematode, allowed a dramatic decrease of the use of nematicides. Subsequently the population of the free living nematodes and the root-knot nematodes ( Meloidogyne spp.) has increased. Among the root-knot nematodes, three Meloidogyne species are important in the potato cultivation in The Netherlands: M. hapla , M. chitwoodi and M. fallax . The latter two species are the most harmful because they cause malformation in the tubers and are quarantine organisms. Until now no resistant potato cultivars are available. Several wild species of potato show resistance, but several back crossings are required to develop a root-knot nematode resistant potato cultivar. Selection based on molecular markers will speed up this development and will replace the expensive and time consuming bioassays, which have to be carried out under strict quarantine conditions. In this thesis diploid as well as polyploid wild Solanum species are used for the introgression of resistance genes in cultivated potato, and to analyse the inheritance of the various resistances.Chapter 2 describes the genetic analysis of the diploid wild species Solanum chacoense with resistance against M. hapla and M. fallax. An AFLP based linkage map was constructed, resulting in twelve linkage groups of either parent of the mapping population with a total length of 685 and 596 cM each. Due to the large differences in AFLP patterns between S. chacoense and cultivated potato, chromosome numbers could not be assigned to the linkage groups containing the QTLs. Two QTLs for resistance against the M. hapla population Hi were identified in this population. These two QTLs, R Mh-chc A and R Mh-chc B , explained 38% and 13% of the total phenotypic variance of the resistance to M. hapla . As a consequence of the large variation in the results of the bioassay, phenotypic selection may lead to the loss of these resistance QTLs. This loss can be prevented by marker assisted selection with the markers flanking the QTLs. The genetic analysis of the resistance against M. fallax resulted in the detection of one QTL explaining 14% of the phenotypic variance. The high level of resistance to M. fallax as observed in the resistant parent was not observed in the progeny. In view of the modest results that can be expected from S. chacoense , we cannot recommend breeding efforts with this germplasm. Better results in genetic analyses and introgression of resistance against M. fallax were achieved in the mapping studies with the wild Solanum species S. fendleri (Chapter 5), S. hougasii and S. bulbocastanum (Chapter 6).The differential interaction of eight M. hapla populations to the resistance QTLs, R Mh-chc A and R Mh-chc B was studied in Chapter 3. The R Mh-chc A allele allows recognition on virulence factors present in all six tested cytological race A populations. Although the allele R Mh-chc B also showed a reduction in the amount of formed egg masses of population Ham, this allele had only an additive effect with population Hi, the population initially used for the QTL analysis (Chapter 2). No effect of both alleles was noticed for the two race B populations. Besides the distinctive difference in reproduction between race A and B, both races can now also be divided based on their differences in virulence to the R Mh-chc A allele. Furthermore, the molecular fingerprints allow too clearly distinguish between the races A and B. Because the resistant parent of the mapping population is susceptible to the race B populations, it is not worthwhile to check the used mapping population for other resistance QTLs. The breeder should therefore search for new sources of resistance to the race B populations in the wild species. Looking at the higher level of reproduction, the population Han would be the most appropriate population to be used in that survey.In Chapter 4 the diploid wild species S. tarijense was used as the source of resistance to M. hapla. The non absolute level of resistance and the continuous distribution of produced egg masses in the segregating offspring, suggests that the resistance is under polygenic control. Therefore a linkage map of the BC1 mapping population was developed as prerequisite of QTL analysis. The assignment of a chromosome number to the linkage groups was simple, because a detailed genetic map was already constructed of the susceptible parent. The linkage groups of the resistant female parent were subsequently aligned to the genetic map of the susceptible male parent using the AFLP markers that were heterozygous in both parents (so-called ab×ab markers). The QTL mapping approach resulted in only one locus, R Mh-tar , on chromosome 7. In contrast to QTL analysis that leads to a broad QTL interval, qualification of the resistance will lead to a more precise map position of the resistance locus. For that case the progeny of the mapping population was arbitrary classified in two groups: 1) a resistant group with the amount of less than1 egg mass and 2) a susceptible group with more than 10 egg masses. Via this approach the R Mh-tar resistance gene could be located on a distal position of the short arm of chromosome 7, and the low amount of singletons offered an indirect validation of the classification of the resistance phenotypes in discrete groups. The value of the R Mh-tar gene for the potato breeding is depending on the allele frequency of the associated virulence genes in the M. hapla populations and the geographic distribution of such populations.In contrast to the research with M. hapla as described in Chapter 2 and 4, the progeny of the mapping populations with resistance against M. chitwoodi and M. fallax (Chapter 5 and 6) could be easily classified as resistant or susceptible. This suggests that resistance is mediated by a single R-gene. The resistance against both nematode species, M. chitwoodi and M. fallax , was absolutely correlated in all three mapping populations, derived from S. fendleri (Chapter 5), S. hougasii and S. bulbocastanum (Chapter 6). In Chapter 5 the monogenic resistance against M. chitwoodi and M. fallax was mapped in an inter-specific and an intra-specific mapping population of the tetraploid wild species S. fendleri . By using the so-called Bulked Segregant Analysis (BSA) method, a large amount of closely linked markers was identified efficiently. In the intra-specific mapping population a remarkably lower amount of linked AFLP markers was found. This can be due to the fact that S. fendleri is a self-fertilising species, showing a lower level of genetic polymorphisms. On the other hand the genetic dissimilarity between the wild species introgression segments and the recurrent potato parents may have caused an elevated level of polymorphic markers in the BC 2 inter-specific mapping population. Besides the larger amount of polymorphic markers, the utilisation of inter-specific mapping populations is an advantage for the breeder, because back-crossings are already made, necessary to introgress the resistance into potato. Based on the sequence of an R Mc1-fen locus linked AFLP marker, a PCR marker was developed. This marker was used to map its position in a reference map, were it was located on the distal position of the long arm of chromosome 11. The chromosomal position of the R Mc1-fen locus was confirmed by using the chromosome 11 specific CAPS marker M39b. The R Mc1-fen gene is located in a cluster of resistance genes, containing the highly related Rmc1 gene and other fungus, virus and nematode resistance genes. This PCR marker, however, can not yet be used in marker assisted selection because 40% of the progeny with the PCR product will not contain the resistance allele.Chapter six describes the localisation of resistance against M. chitwoodi and M. fallax in a BC2 population of the hexaploid wild species S. hougasii . Also this study used the BSA method, resulting in a linkage group of 14 AFLP markers and the monogenic resistance locus R Mc1-hou . Similar to the linkage group of S. fendleri, the linkage group of S. hougasii has been positioned on the distal position of the long arm of chromosome 11.The differential interaction between the resistance genes R Mc1-blb , R Mc1-fen and R Mc1-hou with six M. chitwoodi populations has been studied. Differences in virulence were not found between race 1 and race 2, but, remarkably, within the two races. Populations Ccl and Cbh seem to have a similar virulence spectrum, while these populations are described as respectively race 1 and race 2. The presence of virulence in the populations will have a negative effect on the durability of the resistance. Because the three resistance genes against M. chitwoodi and M. fallax from the wild species S. bulbocastanum , S. fendleri and S. hougasii are mapped on the same locus and act against the same spectrum of virulence genes, no additional value is expect from the strategy of pyramiding these genes. Consequently, the breeder has to search for new resistance sources against the virulent nematode population Ccl and/or Cbh, in order to develop a potato with broad spectrum resistance.The resistance genes described in this thesis can be introgressed in potato with the help of molecular markers. Moreover the presence of individual resistance genes can be monitored by molecular markers, which is a prerequisite for pyramiding of R-genes. Pyramiding of the resistance genes may lead to a resistance with a broader spectrum, and/or may offer a more durable resistance, providing that it can be performed with loci with a complementary resistance spectrum.

We studied the effect of the Russian wheat aphid (RW A) (Diuraphis noxia) infestation on seedlings and adult plants of eight Kenyan wheat (Triticum aestivum L.) varieties. The Kenyan varieties were 91B33, Fahari, Kwale, Mbuni, Chiriku, Kongoni, Nyangumi and Mbega. Two RW A resistant wheats, Halt and PI 294994, were also tested against Kenyan isolates of the aphid. All the Kenyan varieties were susceptible to RW A when compared with the resistant line PI 294994. Halt, which is a resistant variety developed in the USA, was susceptible to Kenyan isolates of RW A. This indicates that the Kenyan RW A isolates are different from the USA ones. In seedlings, the RW A damage was expressed mainly as leaf chlorosis and leaf rolling, with damage scores increasing with time. Differences among the Kenyan varieties in the extent of leaf chlorosis were observed. The most devastating effect of RW A infestation of adult plants of the Kenyan varieties was the reduction in seed set. The tight rolling of flag leaves caused by the aphid delayed ear emergence, leading to floret sterility. Infestation also reduced the quality of the seeds produced, as shown by increased rate of seed deterioration under accelerated ageing conditions, and reduced seedling vigour. The effect of infestation on seed quality was more pronounced under dry conditions. Morphological and genetic variations within PI 294994 were identified. The PI 294994 plants tested could be separated into three distinct groups, all of which had equally high resistance to Kenyan RW A. One PI 294994 derived line, designated P3, was discovered to require no vernalization and therefore to be suitable for use in a Kenyan breeding programme. Segregation in the Fz populations indicated that resistance in two PI 294994 derived lines (PI and P2) was controlled by two genes (one dominant and one recessive). For P3, the results were inconclusive since in one Fz population the segregation indicated that the resistance was controlled by one dominant gene, whereas in another population the segregation indicated that resistance was due to one dominant and one recessive gene. Work to identify molecular markers linked to RW A resistance genees) in P3 was initiated.

Biologische telers hebben behoefte aan rassen die weerbaar zijn tegen ziekten en plagen omdat ze geen gebruik maken van chemische gewasbescherming. In onderzoek wordt daarom gekeken naar rassen met genetische resistentie en ook gunstigemorfologische en fysiologische eigenschappen. Bij tarwe gaan onderzoekers bijvoorbeeld kijken of de compactheid van de aar de weerstand tegen de schimmel fusarium verhoogt. Of ze zoeken naar peenrassen die verlost zijn van zwarte vlekken. Onderzoekershebben peenrassen gevonden die redelijk bestand zijn tegen de schimmels die zwarte vlekkenziekte veroorzaken. Het gaat om primitieve rassen die een witte peen opleveren. Door te kruisen met een oranje peen en vervolgens nakomelingen hiervan weer terug tekruisen, kan uiteindelijk een ras ontstaan dat geschikt is voor de praktijk. Meer over dit verdelingsonderzoek in BOB 24.

We studied the effect of the Russian wheat aphid (RW A) (Diuraphis noxia) infestation on seedlings and adult plants of eight Kenyan wheat (Triticum aestivum L.) varieties. The Kenyan varieties were 91B33, Fahari, Kwale, Mbuni, Chiriku, Kongoni, Nyangumi and Mbega. Two RW A resistant wheats, Halt and PI 294994, were also tested against Kenyan isolates of the aphid. All the Kenyan varieties were susceptible to RW A when compared with the resistant line PI 294994. Halt, which is a resistant variety developed in the USA, was susceptible to Kenyan isolates of RW A. This indicates that the Kenyan RW A isolates are different from the USA ones. In seedlings, the RW A damage was expressed mainly as leaf chlorosis and leaf rolling, with damage scores increasing with time. Differences among the Kenyan varieties in the extent of leaf chlorosis were observed. The most devastating effect of RW A infestation of adult plants of the Kenyan varieties was the reduction in seed set. The tight rolling of flag leaves caused by the aphid delayed ear emergence, leading to floret sterility. Infestation also reduced the quality of the seeds produced, as shown by increased rate of seed deterioration under accelerated ageing conditions, and reduced seedling vigour. The effect of infestation on seed quality was more pronounced under dry conditions. Morphological and genetic variations within PI 294994 were identified. The PI 294994 plants tested could be separated into three distinct groups, all of which had equally high resistance to Kenyan RW A. One PI 294994 derived line, designated P3, was discovered to require no vernalization and therefore to be suitable for use in a Kenyan breeding programme. Segregation in the Fz populations indicated that resistance in two PI 294994 derived lines (PI and P2) was controlled by two genes (one dominant and one recessive). For P3, the results were inconclusive since in one Fz population the segregation indicated that the resistance was controlled by one dominant gene, whereas in another population the segregation indicated that resistance was due to one dominant and one recessive gene. Work to identify molecular markers linked to RW A resistance genees) in P3 was initiated.

Biologische telers hebben behoefte aan rassen die weerbaar zijn tegen ziekten en plagen omdat ze geen gebruik maken van chemische gewasbescherming. In onderzoek wordt daarom gekeken naar rassen met genetische resistentie en ook gunstigemorfologische en fysiologische eigenschappen. Bij tarwe gaan onderzoekers bijvoorbeeld kijken of de compactheid van de aar de weerstand tegen de schimmel fusarium verhoogt. Of ze zoeken naar peenrassen die verlost zijn van zwarte vlekken. Onderzoekershebben peenrassen gevonden die redelijk bestand zijn tegen de schimmels die zwarte vlekkenziekte veroorzaken. Het gaat om primitieve rassen die een witte peen opleveren. Door te kruisen met een oranje peen en vervolgens nakomelingen hiervan weer terug tekruisen, kan uiteindelijk een ras ontstaan dat geschikt is voor de praktijk. Meer over dit verdelingsonderzoek in BOB 24.

Half of all insect species are dependent on living plant tissues, consuming about 10% of plant annual production in natural habitats and an even greater percentage in agricultural systems, despite sophisticated control measures. Plants are generally remarkably well-protected against insect attack, with the result that most insects are highly specialized feeders. The mechanisms underlying plant resistance to invading herbivores on the one side, and insect food specialization on the other, are the main subjects of this book. For insects these include food-plant selection and the complex sensory processes involved, with their implications for learning and nutritional physiology, as well as the endocrinological spects of life cycle synchronization with host plant phenology. In the case of plants exposed to insect herbivores, they include the activation of defence systems in order to minimize damage, as well as the emission of chemical signals that may attract natural enemies of the invading herbivores and maybe exploited by neighbouring plants that mount defences as well.

The cocoa tree ( Theobroma cacao L.) produces the beans that are the source of cacao, the basis for chocolate production, and an important commodity crop in South America, West Africa, and Southeast Asia.Cocoa Pod Borer (CPB,( Conopomorpha cramerella)has been the single most important limiting factor for cacao production in Southeast Asia.So far, there has been no single cost effective and environmentally safe way to control this pest.This thesis describes the first steps in a biotechnological approach to the control of CPB through the production of transgenic cocoa trees, which produce an insecticidal toxin from Bacillus thuringiensis (Bt) in their pod wall, making them resistant to CPB. Selection of a CPB-active toxin, optimization of its expression, making the expression tissue-specific and optimization of cocoa transformation and regeneration are described. Moreover, the isolation of two transcription factor genes involved in flower timing and architecture is described.

The cocoa tree ( Theobroma cacao L.) produces the beans that are the source of cacao, the basis for chocolate production, and an important commodity crop in South America, West Africa, and Southeast Asia.Cocoa Pod Borer (CPB,( Conopomorpha cramerella)has been the single most important limiting factor for cacao production in Southeast Asia.So far, there has been no single cost effective and environmentally safe way to control this pest.This thesis describes the first steps in a biotechnological approach to the control of CPB through the production of transgenic cocoa trees, which produce an insecticidal toxin from Bacillus thuringiensis (Bt) in their pod wall, making them resistant to CPB. Selection of a CPB-active toxin, optimization of its expression, making the expression tissue-specific and optimization of cocoa transformation and regeneration are described. Moreover, the isolation of two transcription factor genes involved in flower timing and architecture is described.