Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Schmallenberg virus detection in bovine semen after experimental infection of bulls.
Poel, W.H.M. van der; Parlevliet, J.M. ; Verstraten, E.R.A.M. ; Kooi, E.A. ; Hakze-van der Honing, R.W. van der; Stockhofe-Zurwieden, N. - \ 2014
Epidemiology and Infection 142 (2014)07. - ISSN 0950-2688 - p. 1495 - 1500.
antibodies - cattle
To study Schmallenberg virus (SBV) excretion in bovine semen after experimental infection, two bulls were inoculated subcutaneously with a SBV isolate (1 ml Vero cell culture 106 TCID50). After inoculation (at day 0), semen was collected daily from both animals for 21 days and samples were tested for SBV by qRT–PCR assay. At 24 days post-inoculation both animals were subjected to necropsy and the genital organs and lymph nodes draining these organs were also tested for SBV RNA (qRT–PCR). After SBV infection both animals in the study showed viraemia (qRT–PCR) with fever and diarrhoea. SBV RNA could be detected in semen from both animals. The highest SBV RNA concentrations in semen were found in the first week (days 4–7 post-inoculation) but concentrations were relatively low (Ct values 30–39). Viable SBV was only isolated from blood samples and not from semen or genital tissues.
Evidence fr a Minor Gene-for-Minor Gene Interaction Explaining Nonhypersensitive Polygenic Partial Disease Resistance
González, A.M. ; Marcel, T.C. ; Niks, R.E. - \ 2012
Phytopathology 102 (2012)11. - ISSN 0031-949X - p. 1086 - 1093.
barley leaf rust - quantitative trait loci - isolate-specific qtls - near-isogenic lines - plant immune-system - puccinia-hordei - durable resistance - development stage - broad-spectrum - latent period
Partial resistance is a quantitative type of resistance that, by definition of Parlevliet, is not based on hypersensitivity. It is largely pathotype nonspecific, although some minor isolate-specific responses have been reported. In order to elucidate the isolate specificity of individual genes for partial resistance, three barley recombinant inbred line mapping populations were analyzed for resistance to the leaf rust fungus Puccinia hordei. The mapping populations were inoculated with one isolate avirulent and two isolates virulent to resistance gene Rph7g. Six significant quantitative trait loci (QTLs) were detected. Of these, two (Rphq3 and Rphq11) were detected with only the avirulent isolate (1.2.1.) and one (Rphq18) only with both virulent isolates (CO-04 and 28.1). The effectiveness of these QTLs was tested with 14 isolates, using a tester set of genotypes containing alleles for resistance or susceptibility for these QTLs. QTL Rphq18 was effective to only two isolates, CO-04 and 28.1, whereas Rphq3 and Rphq11 were ineffective to CO-04 and 28.1 but effective to all other isolates, except one. This resulted in a significant Person's differential interaction, which is a hallmark of a gene–for–gene interaction. The minor gene–for–minor gene interaction is not based on hypersensitivity and there is no evidence that the resistance is based on genes belonging to the nucleotide-binding leucine-rich repeat class.
Breeding crops with resistance to diseases and pests
Niks, R.E. ; Parlevliet, J.E. ; Lindhout, P. ; Bai, Y. - \ 2011
Wageningen : Wageningen Academic Publishers - ISBN 9789086861712 - 198
resistentieveredeling - plantenveredeling - ziekteresistentie - plaagresistentie - plant-microbe interacties - verdedigingsmechanismen - studieboeken - resistance breeding - plant breeding - disease resistance - pest resistance - plant-microbe interactions - defence mechanisms - textbooks
Up-to-date textbook targeted towards students in plant sciences. The book describesthe most basic elements in plant pathogen interactions and defence strategies in plants. The scientific background is explained as far as it is relevant for breeders to make sensible choices in designing and running their breeding work
Effect of partial resistance to barley leaf rust, Puccinia hordei, on the yield of three barley cultivars
Ochoa, J. ; Parlevliet, J.E. - \ 2007
Euphytica 153 (2007)3. - ISSN 0014-2336 - p. 309 - 312.
grain-yield - spring barley - brown rust - wheat - weight - leaves - mildew - race
Three barley cultivars, Shyri, Clipper and Terán, with different levels of partial resistance to barley leaf rust, caused by Puccinia hordei, were exposed to six levels of the pathogen. These levels were obtained by 5, 4, 3, 2, 1 and 0 fungicide (Propiconazol) applications respectively and occurred every 15 days starting at 66 days after sowing. No application served as the control treatment. There were three replicates. The six-row plots were surrounded by a row of a highly susceptible barley cultivar in which the barley leaf rust arrived naturally in a fairly early plant stage. The disease severity was assessed five times with 15 days intervals starting at 66 days after sowing. The yields were determined by harvesting the inner four rows of the plots. An analysis of variance was carried out on the area under the disease progress curve (AUDPC) data and on the yield data. `Shyri¿ was the least susceptible cultivar, `Terán¿ the most. The percentage yield losses varied with the six levels of pathogen from 0 to 31.5% (`Shyri¿), from 0 to 46% (`Clipper¿) and from 0 to 63.5% (`Terán¿). The yield losses correlated strongly with the AUDPC, the linear correlation coefficient being 0.97. The yield losses indicate the importance of the pathogen in Ecuador. It also means that high levels of partial resistance are needed to prevent significant yield damage.
Characterization of the resistance to Phytophthora infestans in local potato cultivars in Bolivia
Gabriel, J. ; Coca, A. ; Plata, G. ; Parlevliet, J.E. - \ 2007
Euphytica 153 (2007)3. - ISSN 0014-2336 - p. 321 - 328.
late blight - field-resistance - bary
This experiment was carried out to investigate whether and how much field resistance to late blight, caused by Phytophthora infestans, is present in the local cultivated potato germplasm. In total 36 entries were compared in a field experiment in an area highly conducive to late blight development. Of the 36 cultivars 32 were local cultivars belonging to five Solanum species, S. tuberosum (1 accession), S. andigena (18), S. juzepczukii (2), S. stenotomum (9) and S. ajanhuiri (2). The other four cultivars were derived from breeding programmes, one being the Dutch cultivar Alpha used as a highly susceptible control. The 36 cultivars were planted according to a simple 6 × 6 lattice design with three replicates. Each replicate was divided in six incomplete blocks each with six cultivars. The disease severity was assessed weekly during 9 weeks starting 48 days after planting. The area under the disease progress curve (AUDPC) was used as a measure of the field resistance. Nine isolates from surrounding potato fields were tested for their virulence to the resistance genes R1¿R11 using 22 differential cultivars. The components of the field resistance of 19 of these cultivars were compared in the greenhouse using a local isolate with virulence to all known R-genes, except to R9. The nine isolates represented seven races with a race complexity varying from 7 to 10 virulence factors. All isolates carried virulence against R1, R2, R3, R7, R10 and R11, while virulence against R9 was absent. The AUDPC among the 32 local cultivars ranged from very large, significantly larger than that of `Alpha¿ to very small. The AUDPC from S. stenotomum accessions ranged from very large to intermediate, those from S. andigena accessions from large to very small. Especially among the S. andigena accessions interesting levels of field resistance were found. Four components of field resistance were assessed, latency period (LP), lesion size (LS), lesion growth rate (LGR) and relative sporulation area (RSA). All four showed a considerable variation among the cultivars. The LP ranged from 3½ to 6 days. The LS ranged from 225 mm2 to 20 mm2. The LGR varied about six-fold, the RSA more than 10-fold. The components tended to vary in association with one another. LP and LGR were well associated with each other and had a significant correlation with the AUDPC.
Fusarium ear rot and how to screen for resistance in open pollinated maize in the Andean regions
Silva, E. ; Mora, E.A. ; Medina, A. ; Vasquez, J. ; Valdez, D. ; Danial, D.L. ; Parlevliet, J.E. - \ 2007
Euphytica 153 (2007)3. - ISSN 0014-2336 - p. 329 - 337.
graminearum infection - corn - moniliforme - genotype - colonization - fumonisins - mycotoxins - hybrids - fungal
Ears infected with ear rot were collected from five provinces in Ecuador. Of the 44 samples analysed 26 carried Fusarium verticillioides, 11 F. subglutinans, two F. graminearum and five carried fungi different from Fusarium. The pathogenicity of ten isolates, seven of F. verticillioides and three of F. subglutinans, were tested. Per isolate 30 ears of the susceptible cultivar Mishca were inoculated by pricking a steel pin, dipped into a spore suspension, through the husks in the central part of the ear 14 days after mid-silk. Ears inoculated with sterile water and ears without any treatment, natural infection, served as controls. The disease severity (DS) of the ears ranged from 14 to 58% ear rot, the range being similar for both species. The DS of the water control, 19%, was much higher than that of the natural control of 2%. Five strains gave a DS of over 40%, significantly higher than the water control. The DS of the others were similar to the water control. In a series of experiments the effect of various methods of applying Fusarium spores through the husks into young ears were compared. All tested methods resulted in DSs significantly higher than those of the two controls. Inoculation with tooth picks and steel pins dipped in a spore suspension gave similar ear rot percentages. Inoculations at 7 to 14 days after mid-silk produced the highest DS¿s. There was no significant effect of spore concentration on the DS. Cultivars differed considerably, the range being from around 20% to over 50%. Surprisingly, only wounding the husks, the sterile water control, resulted in a fairly high DS, much higher than that of the natural control. As the ranking order of the cultivars after wounding only and after inoculation did not seem to be different from the ranking order of the natural control it is suggested to use in areas with high inoculum pressures like the Andes only wounding by means of a steel pin for screening for resistance to maize ear rot.
Farmers' participation and breeding for durable disease resistance in the Andean region
Danial, D.L. ; Parlevliet, J.E. ; Almekinders, C.J.M. ; Thiele, G. - \ 2007
Euphytica 153 (2007)3. - ISSN 0014-2336 - p. 385 - 396.
crop improvement - varieties - selection - maize
In the Andean region, the Preduza project and its partners combined breeding for durable disease resistance using locally adapted cultivars and farmer participatory methods. The approach taken resembles participatory variety selection (PVS). Farmers participated in the selection of advanced materials, rather than finished cultivars. This paper describes this approach and reports experiences with farmers¿breeders collaboration. As breeders involved farmers as participants, they learned more about the most important criteria of male and female farmers for preferred cultivars in the marginal environments of Andean cropping systems. This approach encouraged the use of locally adapted cultivars (often landraces), made the breeders less dependent on foreign materials, and has resulted in selection and development of new wheat, barley, common bean, quinoa, potato and maize cultivars. Breeding programmes based on crossing locally adapted cultivars followed by selection by the breeders in the early phases of the breeding programmes and by participatory selection with the farmers in the more advanced stages of the breeding programmes appeared successful. It became clear that breeders must be well acquainted with the farmer preferences such as the requirements for specific agronomic, storage, processing and marketing traits. Over a period of five years the centralized formal breeding approach predominantly based on material produced by the international institutes was replaced by decentralized breeding approaches based largely on local germplasm with extensive farmer participation
How to maintain improved cultivars
Parlevliet, J.E. - \ 2007
Euphytica 153 (2007)3. - ISSN 0014-2336 - p. 353 - 362.
seed - barley
Improved cultivars loose their identity and healthiness unless maintained properly. Contaminating and degrading forces, such as outcrossing, volunteer plants, mixing, natural selection, mutation and seed-borne diseases, are at the root of this. Maintenance selection can prevent this deterioration. How it is carried out depends on the reproduction system of the crop. Crops are therefore classified into four categories; typical cross-pollinating crops, self-pollinating crops with a substantial amount of outcrossing, typical self-pollinating crops with little outcrossing, and the vegetatively reproduced crops. Generally some of the ¿breeder seed¿ is used to plant a small plot with spaced plants. A fair number of healthy plants of the cultivar type is selected and the seed is harvested per plant. The progenies of the selected plants are grown in small plots. Non-uniform or deviating plots and plots with a seed-borne disease are removed. The seed of the progenies that are healthy, uniform and similar (and so of the cultivar type) are harvested per progeny to be tested next season on larger plots. The same selection is applied and only the seed of the progenies that are healthy, uniform and similar are harvested together to produce the ¿breeder seed¿. The details of this maintenance selection vary with the reproduction system, the multiplication rate of the crop and the possibilities available to the breeder. Seven crops, potato, common bean, barley, wheat, faba bean, quinoa and maize are discussed here as they represent the different reproduction systems and multiplication rates, while being important Andean food crops.
Production and use of maize seed for sowing in Bolivar, Ecuador
Duijndam, F.P. ; Evenhuis, C.J. ; Parlevliet, J.E. - \ 2007
Euphytica 153 (2007)3. - ISSN 0014-2336 - p. 343 - 351.
In the province of Bolívar in the Andean region 212 farmers, six salesmen and 14 technicians, involved in maize production, were interviewed. The majority of the farmers interviewed were small-holders; 64% of the farmers had a farm size of less than 4.5 ha. Maize is the most important crop and is often grown in association with beans. Most maize, 96%, is soft maize meant for human consumption. The cultivars grown are open pollinated ones. One cultivar, `Guagal', was grown extensively. A few others, among which an improved version of Guagal were of some importance. In the production of maize the farmers consider damage due to insects, wind (lodging), diseases, drought and hail, the low prices for their surplus maize and the high costs of fertilizers, chemicals, sowing seed and labour as the most important constraints. The seed for sowing the next crop mainly came from seed kept from the last harvest. Farmers indicated that they select from the harvested ears the healthy looking larger ones. Kernel type also was a selection criterion. Selection for plant type in the field was rarely done. Of the farmers 71% stored the maize as kernels while 29% stored the seed kept on the ears. The storage was predominantly done somewhere in the house in plastic (56%) or cloth bags (14%), in a pile (13%), just on the floor (4%) or in cans (4%). Some farmers still had seed left from the last sowing and were willing to give a sample for testing. From 32 such samples the quality was assessed by INIAP, the Ecuadorean governmental research and breeding organisation. The samples were consistently of a low quality. Especially the vigour of the seedlings was poor and most of the seeds were infected or contaminated by fungi. In the region a few salesmen offer maize seed for sale of cultivar Guagal at prices affordable by the farmer. Of improved cultivars the prices were higher than most farmers are willing to pay. The technicians considered good seed quality and good maintenance of the cultivars effective methods in obtaining better yields. Many farmers do not have access to seed of INIAP and are not familiar with the improved cultivars.
Quantitative resistance and its components in 16 barley cultivars to yellow rust, Puccinia striiformis f.sp. hordei
Sandoval-Islas, J.S. ; Broers, L.H.M. ; Mora-Aguilera, G. ; Parlevliet, J.E. ; Osada-Kawasoe, S. ; Vivar, H.E. - \ 2007
Euphytica 153 (2007)3. - ISSN 0014-2336 - p. 295 - 308.
wheat leaf rust - adult-plant resistance - stripe rust - spring wheat - development stage - latent period - growth stages - epidemics
Sixteen barley cultivars with a susceptible infection type (IT = 7-8) in the seedling stage to an isolate of race 24 of Puccinia striiformis f. sp. hordei were planted at two locations in México. Disease severity (DS) parameters were assessed for the flag leaf and for the upper three leaves. The cultivars represented at least five levels of quantitative resistance ranging from very susceptible to quite resistant. ¿Granado¿, ¿Gloria/Copal¿ and ¿Calicuchima-92¿ represented the most resistant group and had an IT of 7 or 8. The cultivar × environment interaction variance, although significant, was very small compared with the cultivar variance. The disease severity parameters were highly correlated. The monocyclic parameter DSm, measured when the most susceptible cultivar had reached its maximum DS, was very highly correlated with the area under the disease progress curve (AUDPC), r being 0.98. Components of quantitative resistance were evaluated in two plant stages. In the seedling stage small cultivar effects for the latency period were observed, which were not correlated with the quantitative resistance measured in the field. In the adult plant stage the latency period (LP), infection frequency (IF) and colonization rate (CR) were measured in the upper two leaves. The LP was much longer than in the seedling stage and differed strongly between cultivars. The differences in IF were too large, those in CR varied much less. The components showed association with one another. The LP and IF were well correlated with the AUDPC (r = 0.7-0.8).
Introduction : focusing on breeding for durable disease resistance of the Andean highland food crops
Lindhout, P. ; Danial, D.L. ; Parlevliet, J.E. - \ 2007
Euphytica 153 (2007)3. - ISSN 0014-2336 - p. 283 - 285.
Durability of resistance against fungal, bacterial and viral pathogens; present situation
Parlevliet, J.E. - \ 2002
Euphytica 124 (2002)2. - ISSN 0014-2336 - p. 147 - 157.
In evolutionary sense no resistance lasts forever. The durability of a resistance can be seen as a quantitative trait; resistances may range from not durable at all (ephemeral, or transient) to highly durable. Ephemeral resistance occurs against fungi and bacteria with a narrow host range, specialists. It is characterised by a hypersensitive reaction (HR), major gene inheritance and many resistance genes, which often occur in multiple allelic series and/or complex loci. These resistance genes (alleles) interact in a gene-for-gene way with a virulence genes (alleles) in the pathogen to give an incompatible reaction. The pathogen neutralises the effect of the resistance gene by a loss mutation in the corresponding avirulence allele. The incompatible reaction is not elicited any more and the pathogenicity is restored. The pathogens can afford the loss of many avirulences without loss of fitness. Durable resistance against specialised fungi and bacteria is often quantitative and based upon the additive effects of some to several genes, the resulting resistance being of another nature than the hypersensitive reaction. This quantitative resistance is present to nearly all pathogens at low to fair levels in most commercial cultivars. Durable resistance of a monogenic nature occurs too and is usually of a non-HR type. Resistance against fungi and bacteria with a wide host range, generalists, is usually quantitative and durable. Resistances against viruses are often fairly durable, even if these are based on monogenic, race-specific, HR resistances. The level of specialisation does not seem to be associated with the durability of resistance.
Delivery of genetic gain in the interior of British Columbia
Albricht, M. - \ 2001
University. Promotor(en): J.E. Parlevliet. - S.l. : S.n. - ISBN 9789058083944 - 88
bos- en houtproductenindustrieën - bloei - bevruchting - spanningen - groei - droogte - bosbomen - gibberellinen - zaden - zaailingen - zaadtuinen - plantenveredeling - genetische winst - brits-columbia - canada - forest products industries - forest trees - plant breeding - genetic gain - flowering - growth - drought - fertilization - stresses - gibberellins - seeds - seedlings - seed orchards - british columbia
<p>The forest industry is important for the province of British Columbia, Canada. Timber harvest is regulated on a sustained yield basis. Productivity can be increased by enhanced reforestation, stand tending and tree improvement thus reducing the area needed to provide the required amount of wood so that more forest land can be preserved. Tree breeding is done by selection and progeny testing. Genetic gain is delivered through seed orchards where panmixia and seed production can be enhanced. Drought stress and hormone application appeared useful flower enhancement techniques. In a spruce progeny test strong family by site interactions were found. The polycross and the open pollinated progeny tests gave different estimates of the general combining abilities of the same parents, indicating the inferiority of open pollinated progeny tests. Genetic gains for marginal growing sites appeared very low as well as growth rates themselves. Tree improvement must concentrate on better growing sites. Utilizing genetic gains through shortening rotations can have serious consequences for wood and growing site quality.</p>
Planning, Design and Transformation of Industrial Landscapes in The Netherlands
Parlevliet, G. - \ 2000
In: Conference Proceedings ECLAS Dubrovnik 2000 : Landscape of the Future: The Future of Landscape Architecture Education, Dubrovnik, 2000 / Dr. Branka Anicic Zagreb : Department of Landscape Architecture - p. 77 - 87.
Industrial Landscapes in the Netherlands
Parlevliet, G. - \ 2000
In: The 2000 Symposium on Industrial Park Planning and Development / Chien-yuan Lin. - Taipei, Taiwan : Intelligent Industrial Park, 2000. - ISBN 957-98535-6-8 - p. 2/1 - 2/29.
Durability of resistance against fungal, bacterial and viral pathogens
Parlevliet, J.E. - \ 2000
In: Durable Disease Resistance : Durable Resistance, Ede-Wageningen, 2000. - [S.l.] : [s.n.], 2000 - p. 3 - 3.
Interactions of Fusarium oxysporum f.sp lini, the flax wilt pathogen, with flax and linseed
Kroes, G.M.L.W. ; Loffler, H.J.M. ; Parlevliet, J.E. ; Keizer, L.C.P. ; Lange, W. - \ 1999
Plant Pathology 48 (1999). - ISSN 0032-0862 - p. 491 - 498.
Heading date and resistance to Septoria tritici bloth in wheat not genetically associated.
Arama, P.F. ; Parlevliet, J.E. ; Silfhout, C.H. van - \ 1998
Euphytica 106 (1998). - ISSN 0014-2336 - p. 63 - 68.
Effect of plot size and plot situation on the assessment of resistance in wheat cultivars to Septoria tritici.
Arama, P.F. ; Parlevliet, J.E. ; Silfhout, C.H. van - \ 1998
In: Proc. African Crop Sci. Conf. 3 - p. 951 - 955.
Identification and mapping of genes for partial resistance to Puccinia hordei Otth in barley
Qi, X. - \ 1998
Agricultural University. Promotor(en): P. Stam; P. Lindhout. - S.l. : Qi - ISBN 9789054858881 - 165
puccinia hordei - plantenziekteverwekkende schimmels - gerst - graansoorten - ziekteresistentie - genkartering - genen - identificatie - partiële resistentie - plant pathogenic fungi - barley - cereals - disease resistance - gene mapping - genes - identification - partial resistance
<p>In plant-pathogen systems, qualitative resistance with hypersensitivity has been extensively studied. This resistance can be explained with the gene-for-gene model which has been confirmed at the molecular level. This hypersensitive resistance is widely used in plant breeding programmes. However, this resistance is often not durable because the resistance genes can easily be overcome by new variants of the pathogen. Alternatively, quantitative resistance is widely considered to be more durable. However, the polygenic nature of the resistance in the host and the large experimental error in disease tests hamper its application in plant breeding programmes. These same drawbacks also hampered the study of the genetics and of the mechanism of quantitative resistance.</p><p>Recently, various types of DNA markers have been developed that open a new gateway towards further study of quantitative traits, including quantitative resistance. In this thesis, barley ( <em>Hordeum vulgare</em> L.)-barley leaf rust ( <em>Puccinia</em><em>hordei</em> Otth) is chosen as a model system to study the quantitative resistance. This plant-pathosystem has been extensively studied by Parlevliet and his colleagues at the Department of Plant Breeding of the Wageningen Agricultural University. Several recombinant inbred populations had been developed from crosses between partially resistant cultivars or lines, e.g., 'Vada' and 116-5, and an extremely susceptible line, viz., L94. Two populations, L94 x 'Vada' and L94 x 116-5, were used to generate molecular linkage maps and, consecutively, genes for partial resistance in these populations were identified and mapped to the barley genome.</p><p>In chapter 2, a compilation of publicly available RFLP marker linkage maps of barley is presented. The data from four maps were used to produce an integrated map. The overall order of markers on the individual maps was similar, enabling the construction of this integrated map. The integrated map contained 880 markers, covering 1060 cM. Marker clustering was observed in the centromeric regions of the seven chromosomes.</p><p>The AFLP fingerprint technique was used to generate molecular markers in barley as described in chapter 3. With 24 primer combinations a total of 2188 different amplification products were generated from 16 selected barley lines. The size of these amplification products ranged from 80 to 510 bp. Of these barley lines, L94 versus 'Vada' showed the highest polymorphism rate (29%), and 'Proctor' versus 'Nudinka' showed the lowest (12%). The efficiency of primer combinations for identifying genetic markers was similar for any set of barley lines. By using 24 AFLP primer combinations, more than 100 markers could be generated that segregated in at least two of six crossing combinations, and therefore could be used as common markers to compare linkage maps.</p><p>A high-density AFLP marker linkage map which was constructed using a recombinant inbred population (103 RILs, F <sub>9</sub> ) derived from a cross between L94 and 'Vada' is presented in chapter 4. The constructed map contained 561 AFLP markers, three morphological markers, one disease resistance gene and one STS marker, covering a genetic distance of 1062 cM. Uneven distributions of AFLP markers over the chromosomes and strong clustering of markers around the centromeres were found. A skeletal map with a uniform distribution of markers was extracted from the high-density map, and was applied to detect and map loci underlying partial resistance.</p><p>The same set of 103 RILs was evaluated in the seedling and in the adult plant stages in the greenhouse and in the field for resistance to leaf rust isolates 1.2.1 and 24, and quantitative trait loci (QTLs) for partial resistance to these two isolates were identified and mapped on the L94 x 'Vada' map (chapters 5 and 6, respectively). Six QTLs were identified for partial resistance to isolate 1.2.1. Three QTLs were effective in the seedling stage and contributed approximately 55% to the phenotypic variance. Five QTLs were effective in the adult plant stage and contributed approximately 60% to the phenotypic variance. In addition to the three QTLs that were also effective against isolate 1.2.1. in the seedling stage, an additional QTL for resistance of seedlings to isolate 24 was identified. These four QTLs for resistance to isolate 24 jointly explained more than 45% of total phenotypic variance. Also, six QTLs collectively explained approximately 59% of the phenotypic variance of resistance to isolate 24 in the adult plant stage. Of the eight QTLs detected to be effective in the adult plant stage, three were effective to both isolates and five were effective to only one of the two isolates. The isolate specificity of the QTLs supports the hypothesis of Parlevliet and Zadoks that a minor gene-for-minor gene interaction can occur in partial resistance. Of the ten identified QTLs for resistance to the two isolates in this population, QTLs <em>Rphq2</em> and <em>Rhpq3</em> were the only two effective in both the seedling and the adult plant stages. The remaining QTLs were effective in either of the two developmental stages.</p><p>Chapter 7 present results of mapping QTLs for partial resistance to leaf rust isolate 1.2.1 on another AFLP linkage map which was constructed by using 117 RILs (F <sub>8</sub> ) derived from a cross between L94 and 116-5. Three QTLs were effective in the seedling stage, jointly contributing 42% to the total phenotypic variance. Also, three QTLs were effective in the adult plant stage, collectively explaining 35% of the phenotypic variance. <em>Rphq3</em> , with a major-effect, was the only QTL being effective in both developmental stages. This QTL was also found to be effective in the L94 x 'Vada' population. The remaining QTLs in the L94 x 116-5 population were mapped to different positions on the linkage map than those found in the L94 x 'Vada' population. This suggests that loci for partial resistance to leaf rust are scattered all over the barley genome. Consequently, a strategy to accumulate many resistance genes in a single cultivar is feasible, which would result in a very high level of partial resistance.</p><p>Studies in chapters 5, 6 and 7 showed that map positions of QTLs for partial resistance do not coincide with those of the race-specific resistance genes ( <em>Rph</em> genes), supporting the theory that genes for partial resistance and genes for hypersensitive resistance are entirely different gene families.</p>
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