Genetic diversity among late blight resistant and susceptible potato genotypes

RAPD polymerase chain reaction analysis was used to study the genetic diversity among a wild potato variety Solanum demissum (very resistant to late blight) and six potato cultivars (Hanna, Lady-Olympia, Lady-Rosetta, Spunta, Diamant and Cara) varied in their resistance to Phytophthora infestans. Cluster analysis of six potato genotypes showed that, all tested genotypes were separated into two clusters (1 and 2). Cluster 1, included only the wild potato variety (S. demissum), whereas cluster 2 divided into two groups (G1 and G2). Late blight high resistant cultivars Hanna and Cara were grouped in G1. Group 2 included the moderate resistant cultivar Spunta and the susceptible cultivars Diamant, Lady-Rosetta and Lady-Olympia. The potato cultivars that showed highest genetic similarity to the wild potato variety were the resistant cultivars Hanna and Cara. Lowest genetic similarity was obtained with the susceptible cultivars Lady-Rosetta, Diamant and Lady-Olympia. RAPD primer K17 yielded a band with molecular weight of 936 bp found in all susceptible potato cultivars (Lady-Rosetta, Lady-Olympia and Diamant). On the other hand, band with molecular weight of 765 bp were detected in the wild potato and the resistant cultivars Hanna and Cara. Results of this study suggested that, the RAPD marker technique could be beneficial for revealing the genetic variability of different genotypes of potato varied in their resistibility to late blight.     

Two orthologs of late blight resistance gene <Emphasis Type="Italic">R1</Emphasis> in wild and cultivated potato

The R1 gene for resistance to oomycete Phytophthora infestans (Mont.) de Bary, the causal agent of late blight disease of potato (Solanum tuberosum L.), was initially identified in S. demissum and potato varieties bred by introgressing the S. demissum germplasm. Later a sequence characterized amplified region (SCAR) marker R1-1205 of this gene was also found in S. stoloniferum and S. polytrichon. Here we describe the full-length R1 sequence cloned from S. stoloniferum. This sequence is translatable, and this evidence of structural gene integrity is reinforced by functional characterization of the S. stoloniferum R1 gene in an effectoromics experiment. When screened across a series of S. demissum and S. stoloniferum accessions, the R1 sequences differed by several single nucleotide polymorphisms and an indel; this indel served the basis for constructing SCAR markers R1-517 and R1-513 that reliably discerned two R1 orthologs. The demissum-specific marker R1-517 was found in all S. demissum accessions under study; it was also present in many demissum-derived potato varieties and hybrids. The stoloniferum-specific marker R1-513 was found in 27% of S. stoloniferum and S. polytrichon accessions; however, we failed to discern this marker in the genotypes of cultivated potato listing S. stoloniferum in their pedigrees. Most probably, such absence of R1-513 is best explained by an opportunistic breeding history of stoloniferum-derived founder lines, which were employed first and foremost in breeding for resistance to potato virus Y: eventually, these founder lines are devoid of the R1 gene.     

The R1 gene for potato resistance to late blight (Phytophthora infestans) belongs to the leucine zipper/NBS/LRR class of plant resistance genes

Late blight caused by the oomycete Phytophthora infestans is the most destructive disease in potato cultivation worldwide. New, more virulent P. infestans strains have evolved which overcome the genetic resistance that has been introgressed by conventional breeding from wild potato species into commercial varieties. R genes (for single-gene resistance) and genes for quantitative resistance to late blight are present in the germplasm of wild and cultivated potato. The molecular basis of single-gene and quantitative resistance to late blight is unknown. We have cloned R1, the first gene for resistance to late blight, by combining positional cloning with a candidate gene approach. The R1 gene is member of a gene family. It encodes a protein of 1293 amino acids with a molecular mass of 149.4 kDa. The R1 gene belongs to the class of plant genes for pathogen resistance that have a leucine zipper motif, a putative nucleotide binding domain and a leucine-rich repeat domain. The most closely related plant resistance gene (36% identity) is the Prf gene for resistance to Pseudomonas syringae of tomato. R1 is located within a hot spot for pathogen resistance on potato chromosome V. In comparison to the susceptibility allele, the resistance allele at the R1 locus represents a large insertion of a functional R gene.     

Resistance to late blight in Solanum bulbocastanum is mapped to chromosome 8

Somatic hybrids between potato and Solanum bulbocastanum, a wild diploid (2n=2x=24) Mexican species, are highly resistant to late blight, caused by Phytophthora infestans. Both randomly amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) markers that are closely linked to the resistance have been noted by analysis of three different backcross-2 populations derived from two different somatic hybrids. With reference to previously published potato and tomato maps, resistance appears to be on the long arm of chromosome 8 and is flanked by RFLP markers CP53 and CT64. In a population of BC₂ plants derived from a cross between the BC₁ line J10lK6 [(S. tuberosum PI 203900+S. bulbocastanum PI 243510) ×Katahdin)]×Atlantic, late blight resistance cosegregated with RFLP marker CT88 and RAPD marker OPG02–625. Received: 26 November 1999 / Accepted: 22 December 1999     

Assessing genetic potential in germplasm collections of crop plants by marker-trait association: a case study for potatoes with quantitative variation of resistance to late blight and maturity type

Genetic diversity of crop plants resulting from breeding and selection is preserved in gene banks. Utilization of such materials for further crop improvement depends on knowledge of agronomic performance and useful traits, which is usually obtained by phenotypic evaluation. Associations between DNA markers and agronomic characters in collections of crop plants would (i) allow assessment of the genetic potential of specific genotypes prior to phenotypic evaluation, (ii) identify superior trait alleles in germplasm collections, (iii) facilitate high resolution QTL mapping and (iv) validate candidate genes responsible for quantitative agronomic characters. The feasibility of association mapping was tested in a gene bank collection of 600 potato cultivars bred between 1850 and 1990 in different countries. The cultivars were genotyped with five DNA markers linked to previously mapped QTL for resistance to late blight and plant maturity. Specific DNA fragments were tested for association with these quantitative characters based on passport evaluation data. Highly significant association with QTL for resistance to late blight and plant maturity was detected with PCR markers specific for R1, a major gene for resistance to late blight, and anonymous PCR markers flanking the R1 locus at 0.2 Centimorgan genetic distance. The marker alleles associated with increased resistance and later plant maturity were traced to an introgression from the wild species S. demissum. These DNA markers are the first marker that are diagnostic for quantitative agronomic characters in a large collection of cultivars.     

番茄RGA4蛋白与马铃薯Rpi-blb1蛋白的同源比较分析

为获得番茄抗晚疫病广谱性基因信息,采用同源电子克隆法,基于番茄蛋白序列数据库,以马铃薯晚疫病广谱抗性蛋白Rpi-blb1为种子序列,获得番茄疾病抗性蛋白RGA4,并进行基因电子定位和基因结构、模体、二级结构、基因进化及基因电子表达等分析,以证明两者的进化关系。结果表明:番茄RGA4蛋白(XP_004245923.1)序列具有NB-ARC和LRR8两个保守结构域,定位于第8条染色体SL2.40区间,相应基因位于8号染色体序列的57228847-57232935 bp区间,长度为4 089 bp,由2个外显子和1个内含子组成,编码988个氨基酸序列,该蛋白为不稳定分泌球形蛋白;番茄RGA4蛋白和马铃薯Rpi-blb1蛋白在二级结构分布、基因序列组成、基因定位等方面相似性较高,可确定两者为垂直同源关系,但在基因进化和模体组成方面存在差异,可能导致两者功能上的不同。研究结果可为番茄晚疫病广谱抗性基因克隆及其利用提供理论依据。     

A genetic analysis of quantitative resistance to late blight in potato: towards marker-assisted selection

Late blight caused by the oomycete Phytophthora infestans is the most important fungal disease in potato cultivation worldwide. Resistance to late blight is controlled by a few major genes (R genes) which can be easily overcome by new races of P. infestans and/or by an unknown number of genes expressing a quantitative type of resistance which may be more durable. Quantitative resistance of foliage to late blight was evaluated in five F₁ hybrid families originating from crosses among seven different diploid potato clones. Tuber resistance was evaluated in four of the families. Two of the families were scored for both foliage maturity and vigour. The five families were genotyped with DNA-based markers and tested for linkage with the traits analysed. QTL (quantitative trait locus) analysis identified at least twelve segments on ten chromosomes of potato having genes that affect reproducibly foliage resistance. Two of those segments also have major R genes for resistance to late blight. The segments are tagged by 21 markers that can be analyzed based on PCR (polymerase chain reaction) with specific oligonucleotide primers. One QTL was detected for tuber resistance and one for foliage vigour. Two QTLs were mapped for foliage maturity. Major QTL effects on foliage and tuber resistance to late blight and on foliage maturity and vigour were all linked with marker GP179 on linkage group V of potato. Plants having alleles at this QTL, which increased foliage resistance, exhibited decreased tuber resistance, later maturity and more vigour.     

Argentinian wild diploid Solanum species as sources of quantitative late blight resistance

Greenhouse and field evaluations of quantitative resistance to late blight in genotypes of the wild Argentine diploid species Solanum chacoense, Solanum commersonnii, Solanum microdontum and Solanum maglia were performed with a complex race containing the virulence factors 1, 3, 4, 5, 7,10, 11 of Phytophora infestans and using the percentage of leaf area affected by late blight estimated at weekly intervals. From these readings the area under the disease progress curve (AUDPC) was calculated. Highly resistant and susceptible genotypes were identified. Resistance and variability were found in S. chacoense, which together with S. commersonnii showed a significantly higher level of resistance compared to the susceptible checks. Field evaluations of an F₁ progeny of 165 individuals, obtained from non-inbred diploid parents segregating for foliage quantitative resistance in S. chacoense, were also done by means of AUDPC. The polygenic nature of the resistance and some indication of the presence of both additive and interaction effects were evident. Received: 30 August 1999 / Accepted: 30 December 1999     

基于高通量测序的福建北部马铃薯晚疫病株根际土壤细菌群落分析

[背景]马铃薯晚疫病是一种由致病疫霉[Phytophthora infestans(Mont.)de Bary]引起的毁灭性病害,当环境条件适宜时,残留在土壤中的病原菌会侵染马铃薯植株导致病害的发生.[目的]明确健康马铃薯植株与发病植株的根际土壤细菌结构与多样性.[方法]采集马铃薯晚疫病发病地的健康植株根际土壤(M2J...     

Somatic hybrids between Solanum bulbocastanum and potato: a new source of resistance to late blight

 Solanum bulbocastanum, a wild, diploid (2n=2x=24) Mexican species, is highly resistant to Phytophthora infestans, the fungus that causes late blight of potato. However this 1 EBN species is virtually impossible to cross directly with potato. PEG-mediated fusion of leaf cells of S. bulbocastanum PI 245310 and the tetraploid potato line S. tuberosum PI 203900 (2n=4x=48) yielded hexaploid (2n= 6x=72) somatic hybrids that retained the high resistance of the S. bulbocastanum parent. RFLP and RAPD analyses confirmed the hybridity of the materials. Four of the somatic hybrids were crossed with potato cultivars Katahdin or Atlantic. The BC₁ progeny segregated for resistance to the US8 genotype (A-2 mating type) of P. Infestans. Resistant BC₁ lines crossed with susceptible cultivars again yielded populations that segregated for resistance to the fungus. In a 1996 field-plot in Wisconsin, to which no fungicide was applied, two of the BC₁ lines, from two different somatic hybrids, yielded 1.36 and 1.32 kg/plant under a severe late-blight epidemic. In contrast, under these same conditions the cultivar Russet Burbank yielded only 0.86 kg/plant. These results indicate that effective resistance to the late-blight fungus in a sexually incompatible Solanum species can be transferred into potato breeding lines by somatic hybridization and that this resistance can then be further transmitted into potato breeding lines by sexual crossing. Received: 27 October 1997 / Accepted: 11 November 1997     

Stacking three late blight resistance genes from wild species directly into African highland potato varieties confers complete field resistance to local blight races

Considered responsible for one million deaths in Ireland and widespread famine in the European continent during the 1840s, late blight, caused by Phytophthora infestans, remains the most devastating disease of potato (Solanum tuberosum L.) with about 15%–30% annual yield loss in sub‐Saharan Africa, affecting mainly smallholder farmers. We show here that the transfer of three resistance (R) genes from wild relatives [RB, Rpi‐blb2 from Solanum bulbocastanum and Rpi‐vnt1.1 from S. venturii] into potato provided complete resistance in the field over several seasons. We observed that the stacking of the three R genes produced a high frequency of transgenic events with resistance to late blight. In the field, 13 resistant transgenic events with the 3R‐gene stack from the potato varieties ‘Desiree’ and ‘Victoria’ grew normally without showing pathogen damage and without any fungicide spray, whereas their non‐transgenic equivalent varieties were rapidly killed. Characteristics of the local pathogen population suggest that the resistance to late blight may be long‐lasting because it has low diversity, and essentially consists of the single lineage, 2_A1, which expresses the cognate avirulence effector genes. Yields of two transgenic events from ‘Desiree’ and ‘Victoria’ grown without fungicide to reflect small‐scale farm holders were estimated to be 29 and 45 t/ha respectively. This represents a three to four‐fold increase over the national average. Thus, these late blight resistant potato varieties, which are the farmers’ preferred varieties, could be rapidly adopted and bring significant income to smallholder farmers in sub‐Saharan Africa.     

The Rpi-blb2 gene from Solanum bulbocastanum is an Mi-1 gene homolog conferring broad-spectrum late blight resistance in potato

The necessity to develop potato and tomato crops that possess durable resistance against the oomycete pathogen Phytophthora infestans is increasing as more virulent, crop-specialized and pesticide resistant strains of the pathogen are rapidly emerging. Here, we describe the positional cloning of the Solanum bulbocastanum-derived Rpi-blb2 gene, which even when present in a potato background confers broad-spectrum late blight resistance. The Rpi-blb2 locus was initially mapped in several tetraploid backcross populations, derived from highly resistant complex interspecific hybrids designated ABPT (an acronym of the four Solanum species involved:S. acaule, S. bulbocastanum, S. phureja and S. tuberosum), to the same region on chromosome 6 as the Mi-1 gene from tomato, which confers resistance to nematodes, aphids and white flies. Due to suppression of recombination in the tetraploid material, fine mapping was carried out in a diploid intraspecific S. bulbocastanum F1 population. Bacterial artificial chromosome (BAC) libraries, generated from a diploid ABPT-derived clone and from the resistant S. bulbocastanum parent clone, were screened with markers linked to resistance in order to generate a physical map of the Rpi-blb2 locus. Molecular analyses of both ABPT- and S. bulbocastanum-derived BAC clones spanning the Rpi-blb2 locus showed it to harbor at least 15 Mi-1 gene homologs (MiGHs). Of these, five were genetically determined to be candidates for Rpi-blb2. Complementation analyses showed that one ABPT- and one S. bulbocastanum-derived MiGH were able to complement the susceptible phenotype in both S. tuberosum and tomato. Sequence analyses of both genes showed them to be identical. The Rpi-blb2 protein shares 82% sequence identity to the Mi-1 protein. Significant expansion of the Rpi-blb2 locus compared to the Mi-1 locus indicates that intrachromosomal recombination or unequal crossing over has played an important role in the evolution of the Rpi-blb2 locus. The contrasting evolutionary dynamics of the Rpi-blb2/Mi-1 loci in the two related genomes may reflect the opposite evolutionary potentials of the interacting pathogens.     

Differential gene expression in two potato lines differing in their resistance to Phytophthora infestans

Horizontal resistance to late blight in the potato is a primary objective of many breeding programs. Knowledge of the physiological and biochemical mechanisms underlying it, however, is scarce. The purpose of the present study was the identification of these physiological and biochemical factors in plant material obtained by crossing a late blight resistant Solanum phureja clone with a susceptible dihaploid of S. tuberosum subsp. tuberosum. The mRNA RT-PCR differential display method was used to compare the gene expression patterns of a resistant hybrid with that of a susceptible one. By sequence homology, we identified several genes with diverse functions, including genes known to be involved in resistance or stress responses and genes known to be involved in primary or secondary metabolism.     

Fine mapping of the Ph-3 gene conferring resistance to late blight (Phytophthora infestans) in tomato

Late blight, caused by the oomycete pathogen Phytophthora infestans (Mont.) de Bary, is a devastating disease for tomato and potato crops. In the past decades, many late blight resistance (R) genes have been characterized in potato. In contrast, less work has been conducted on tomato. The Ph-3 gene from Solanum pimpinellifolium was introgressed into cultivated tomatoes and conferred broad-spectrum resistance to P. infestans. It was previously assigned to the long arm of chromosome 9. In this study, a high-resolution genetic map covering the Ph-3 locus was constructed using an F₂ population of a cross between Solanum lycopersicum CLN2037B (containing Ph-3) and S. lycopersicum LA4084. Ph-3 was mapped in a 0.5 cM interval between two markers, Indel_3 and P55. Eight putative genes were found in the corresponding 74 kb region of the tomato Heinz1706 reference genome. Four of these genes are resistance gene analogs (RGAs) with a typical nucleotide-binding adaptor shared by APAF-1, R proteins, and CED-4 domain. Each RGA showed high homology to the late blight R gene Rpi-vnt1.1 from Solanum venturii. Transient gene silencing indicated that a member of this RGA family is required for Ph-3-mediated resistance to late blight in tomato. Furthermore, this RGA family was also found in the potato genome, but the number of the RGAs was higher than in tomato.     

Evaluation of fungicides to control potato late blight (Phytophthora infestans) in the plains of Nepal

Fungicide application is an effective management option to control late blight of potato (caused by Phytophthora infestans). Field experiments were conducted to evaluate the efficacy of recently introduced and previously used fungicides on late blight management and potato yields in the western plains of Nepal in 2015 and 2016 crop seasons. Fungicides and a non-treated control (NTC) were replicated three times in a randomized block design planted with late blight susceptible cultivar Cardinal. Chlorothalonil, copper oxychloride, dimethomorph, fenamidone + mancozeb, mancozeb and metalaxyl were sprayed in 2015. In 2016, carbendazim was used instead of chlorothalonil. The area under disease progress curve (AUDPC) was consistently reduced in years by dimethomorph (90% and 65% in 2015 and 2016, respectively), fenamidone + mancozeb (68% and 62%) and mancozeb (40% and 47%) compared with the NTC. Similarly, tuber yield was increased with the application of dimethomorph (266% and 146% in 2015 and 2016, respectively), fenamidone + mancozeb (211% and 155%) and mancozeb (136% and 116%) compared with the NTC. Chlorothalonil reduced AUDPC by 43% and increased tuber yield by 170% in 2015. Other fungicides either had inconsistent results or did not reduce late blight severity and consequent effects on potato yield. The overall benefit–cost ratio was highest for dimethomorph in both years. These results show efficacy of dimethomorph, fenamidone + mancozeb and mancozeb in reducing late blight severity and increasing potato tuber yield in the plains of Nepal.     

Autotetraploids and genetic mapping using common AFLP markers: the R2 allele conferring resistance to Phytophthora infestans mapped on potato chromosome 4

 Due to the complexity of tetrasomic inheritance, mapping studies in potato (Solanum tuberosum L.) are generally conducted at the diploid level. In the present study we tested the feasibility of Bulked Segregant Analysis (BSA) using a tetraploid offspring for the identification of AFLP markers linked to the R2 allele, which confers race-specific resistance to Phytophthora infestans. Eleven bulk-specific AFLP markers, detected in fingerprints of 205 AFLP primer combinations, could be mapped in a linkage group encompassing the R2 locus. The efficiency of BSA at the tetraploid level, determined by the frequency of single-dose restriction fragments (SDRF), was much higher than expected on the basis of overall genetic dissimilarity between the parental clones. The fortuitous detection of AFLPs with linkage to the R2 allele is explained on the basis of specific genetic dissimilarity between cultivated potato and the chromosomal segment introgressed from S. demissum carrying the resistant R2 allele. AFLP markers common to those with linkage to R2 were visually recognized by their electrophoretic mobility in the AFLP fingerprint in a parental clone of a reference mapping population. Using these common AFLP markers we anchored the linkage group comprising the R2 allele to potato chromosome 4. Received: 30 October 1997 / Accepted: 6 November 1997     

Effect of orange essential oil and its constitutes on late blight disease of potato plants under field conditions

Late blight caused by Phytophthora infestans is the most important disease attacking potato plants. Four concentrations of essential oils i.e. 0.0, 1.25, 2.5, 5.0 and 7.5 ml/l of Orange, Citral, Methyl antranate (MA), and Terbinol were tested for controlling late blight disease. Results indicate that all treatments except orange oil have an inhibitory effect against the linear growth of P. infestans. Complete reduction in linear growth was obtained with Citral and MA at concentrations of 5.0 and 7.5 ml/l. Other treatments showed moderate effect against P. infestans. In greenhouse experiments, results indicate that all treatments have protective and therapeutic effects against late blight disease except Orange oil which has a protective effect only. High reduction was obtained with Citral and MA at concentrations of 2.5 and 5.0 ml/l which reduced the disease severity by more than 77.1 and 62.8% when applied as protective and therapeutic treatments respectively. Moderate effect was obtained with orange oil and Citral at concentration of 7.5 ml/l for both treatments which reduced the disease severity by more than 65.7% when applied as protective treatments. Similar results were obtained under field coditions; results indicate that all treatments reduced the late blight severity during two growing seasons. High reduction was obtained with Citral and MA at concentrations of 2.5 and 5.0 ml/l which reduced the disease severity by more than 80.0%. As for potato yield, results indicate that all treatments increased potato yield during two growing seasons. A high increase was obtained with Citral and MA at concentrations of 2.5 and 5.0 ml/l which increased the potato yield by more than 59.1%. Other treatments showed a moderate increase. It could be suggested that some essential oils of citrus or their constituents might be used for controlling late blight disease potato plants under field conditions.     

Efficacy of fungicide combinations,phosphoric acid and plant extract from stinging nettle on potato late blight management and tuber yield

Late blight caused by Phytophthora infestans is a major constraint to potato production. Inadequate control of the disease has often resulted in potato yield losses. We assessed the efficacy of fungicides, phosphoric acid and stinging nettle extract combinations for late blight control at two locations in Kenya. Disease severity, relative area under disease progress curves (RAUDPC), pathogen lesions and tuber yield were quantified during the 2008 and 2009 cropping cycles. The application of metalaxyl alternated with phosphate resulted in the greatest suppressive effects on late blight. The average late blight severity ranged from 3.5 to 34% in 2008 and 4.7 to 50% in 2009 at Tigoni location. RAUDPC for the same location ranged from 5 to 40% and 5 to 50% in 2008 and 2009, respectively. Similar levels of late blight severity were recorded at Marimba location in both years. Lesion growth and pathogen lesion numbers on potato plants differed significantly (p < 0.05) among treatments. Fungicides, phosphoric acid and stinging nettle extract varied in late blight control. Potato tuber yield varied among treatments. Phosphoric acid treatment had significantly (p < 0.05) greater tuber yield compared to metalaxyl at both locations. Field plots treated with plant extracts from stinging nettle resulted in the lowest tuber yield compared to other treatments with the exception of the untreated control. Fungicides, phosphoric acid, stinging nettle extract and their combinations can be readily effective in the suppression of late blight severity and pathogen lesions with moderate increases in tuber yield.     

Broad spectrum late blight resistance in potato differential set plants Ma<Emphasis Type="Italic">R8</Emphasis> and Ma<Emphasis Type="Italic">R9</Emphasis> is conferred by multiple stacked <Emphasis Type="Italic">R</Emphasis> genes

Phytophthora infestans is the causal agent of late blight in potato. The Mexican species Solanum demissum is well known as a good resistance source. Among the 11 R gene differentials, which were introgressed from S. demissum, especially R8 and R9 differentials showed broad spectrum resistance both under laboratory and under field conditions. In order to gather more information about the resistance of the R8 and R9 differentials, F1 and BC1 populations were made by crossing Mastenbroek (Ma) R8 and R9 clones to susceptible plants. Parents and offspring plants were examined for their pathogen recognition specificities using agroinfiltration with known Avr genes, detached leaf assays (DLA) with selected isolates, and gene-specific markers. An important observation was the discrepancy between DLA and field trial results for Pi isolate IPO-C in all F1 and BC1 populations, so therefore also field trial results were included in our characterization. It was shown that in MaR8 and MaR9, respectively, at least four (R3a, R3b, R4, and R8) and seven (R1, Rpi-abpt1, R3a, R3b, R4, R8, R9) R genes were present. Analysis of MaR8 and MaR9 offspring plants, that contained different combinations of multiple resistance genes, showed that R gene stacking contributed to the Pi recognition spectrum. Also, using a Pi virulence monitoring system in the field, it was shown that stacking of multiple R genes strongly delayed the onset of late blight symptoms. The contribution of R8 to this delay was remarkable since a plant that contained only the R8 resistance gene still conferred a delay similar to plants with multiple resistance genes, like, e.g., cv Sarpo Mira. Using this “de-stacking” approach, many R gene combinations can be made and tested in order to select broad spectrum R gene stacks that potentially provide enhanced durability for future application in new late blight resistant varieties.